Salomon S Lab X-Series Update – a continuing great performer

I have reviewed the Salomon S Lab X-Series “road” shoe previously with initial impressions here and, after some use on varied terrain, in comparison to the S Lab Sense 4 Ultra trail shoe here. Initial and continued use of the S Lab X-series “road” shoe revealed that it not only performs very well on roads but also on the trails, at least on the trails here in the Northern Rocky Mountains of the US.  This post is an update after considerable additional use of the X-Series on a wide variety of terrain.

I now have about 700 km (435 miles) on a first pair of X-Series and have recently introduced a second pair of X-Series in rotation. A third pair is being set aside for races. As should be obvious, I have committed entirely to the use of the X-Series for all trail and ultra-trail races and associated training going forward in 2015. When compared to the Sense 4 Ultra, the X-Series has sufficient trail prowess to be a good choice for all but the most demanding of technical trails (think Trofeo as an example of where you might choose the Sense 4 over the X-Series). At the same time the X-Series offers significantly increased comfort over the Sense 4, particularly on long (>30 km) runs. The following is a summary of my experience using the X-Series “road” shoe on trails.


As expected from a “road”- trail hybrid shoe, performance on flatter and buffed trails is outstanding. But, as has been indicated in previous reviews, the X-Series exhibits surprising performance on trails in general and specifically on rocky and “technical” sections, both on the ups and the downs. Based on the Salomon literature and introduction material, the X-Series was not designed as an all-around trail shoe, yet my experience is that it is and it is a great performer.

The X-Series has continued to shine on anything that the Rockies can dole out with the exception of deep mud where the larger platform and ground contact area of the X-Series lead to a fair bit of “float” when compared to the Sense 4 and FellCross 3*. I have been able to run with confidence on all of the trails that I have run in the Sense line in the past 3 years and notice very little if any difference in performance. What is different is comfort, where the X-Series is much superior, at least on my 60 year old feet. It is not clear why the X-Series is so comfortable on longer runs, although I suspect that the midsole design in the midfoot is playing a large role. Overall from a performance perspective, I can highly recommend the X-Series as an outstanding trail performer and as a shoe quite ideally suited to ultra trail events.


As noted previously, the X-Series utilizes some materials that have not been seen on Salomon shoes in the past- specifically the Lycra forefoot upper and the super-thin mesh on the outside mid-foot upper. In addition the outsole wear layer is glued onto the midsole material in segments which is a design approach that Salomon have had issues with in the past. These are the areas of the shoe that I have been keeping an eye on.

As of this juncture and with about 700 km (435 miles) of use, it is apparent that these “suspect” areas and the shoe in general is holding up exceedingly well. There is no evidence of excessive wear on any section as can be clearly seen in the following images.



Salomon S Lab X-Series after approximately 700 km (435 miles) of use. No evidence of excessive wear anywhere on the upper, the outsole, or in the construction.

A closer look at the outsole shows that the wear layer is quite durable, more so than what I have experienced with the Sense line of shoes over the past three years. As a supinator I typically see increased wear on the outside of the mid-forefoot and on the outside of the heel area. As can be seen in the image below neither of these areas show an increased wear relative to the rest of the outsole. I am not certain as to why this might be but the increased footprint and increased area of contact may be playing a role. The geometry of the shoe design (including increases in footprint, area of contact, the “rocker” element, and the details of the midsole structure and composition) is likely the reason for such even wear of the outsole.


Outsole of the X-Series after 700 km (435 miles) of trail running including about 30% rocky technical, 60% buffed singletrack, and 10% road use.


I have experienced no significant issues with use of the shoes- the fit has remained excellent, the stability and traction have not diminished, and the materials are holding up well. I have, however had one incident that is making me focus a bit more on the applicability of this shoe in truly technical terrain.

Although this incident could have been entirely stochastic, I have never had such a thing occur in over 35 years of running. While on a long run through some very technical terrain I noticed that there seemed to be a small stone in the shoe. After a while I stopped and took the shoe off and emptied out any debris that had collected inside the shoe. Some small stone chards fell out. I put the shoe back on and continued running however the stone I felt previously seemed to still be in there. So I stopped again and emptied the shoe, something else fell out and I thought that would be it. But after continuing I still felt the stone. So I took the shoe off again and felt very carefully and realized that there was a stone under the insole, something that has never happened to me. I removed the insole and finally found the culprit- it was a small sharp stone that had penetrated through the exposed midsole (EVA) material, through the ProFeel rock plate, and into the interior of the shoe. The following images show this.


Looking into the shoe with the insole removed showing the puncture from a sharp stone.


Image of the outsole, the sharp stone, and the place where the sharp stone penetrated the outsole area (I saved the stone after removing it).


The insole removed where the penetration can be seen in the lower section of the trailing end of the forefoot.


The opposite side of the insole showing the penetration point.


The penetration point on the underside of the insole and the offending sharp stone.

It took quite an effort to remove the sharp stone from the shoe. I was never able to get it back in either. I expect that this was likely a chance event- the right sharp stone in the right orientation, the right location on the sole, and the right placement of the shoe on the stone. But I will be keeping a peeled eye towards any further events- both with or without puncture. It still seems unusual that such a stone would penetrate the ProFeel film, but that seems to have clearly happened.

Bottom Line

The Salomon S Lab X-Series hybrid “road”/trail shoe is an outstanding trail shoe that is very light, has excellent fit, durable upper and outsole, and is exceedingly comfortable on long (>30km) runs. The shoe handles anything from buffed singletrack to highly technical rocky terrain to wet rocks/roots and medium mud. Deep mud conditions will be challenging in this shoe (as they are in the Sense 4 Ultra) so if deep mud is common in your running there are better options.

I can highly recommend this shoe for both training and racing trail and ultra-trail events.


*Generally, US trails do not include wet grass conditions as most trails are developed, are substantially dirt and rock, and it is not encouraged to deviate from the established trail. Fell running on the other hand is very much the opposite. I have not tested the X-Series in “Fell” conditions so all comments here exclude application to Fell running.


Salomon S Lab X-Series vs. Salomon S Lab Sense 4 Ultra – 911 vs. GT3

In a recent review of the Salomon S lab X-Series “road” shoe I hinted that, based on limited trail miles, it seemed that the X-Series might prove to more of a trail shoe than expected. Well, now, after a little less than 200 miles (300 km), I can affirmatively attest to the trail-worthiness of the X-Series. In fact I will go so far as to say that this shoe is hitting an optimum mix of characteristics for all but the most gnarliest of trails- even though Salomon classes it as a “road” shoe with some trail capability.

So, I have tested the X-Series against Salomon’s top-of-the-line trail shoe, the S Lab Sense 4 Ultra. This comparison test has been conducted on all of the same trails, conditions, and terrain. The primary trails are mountainous buffed to mid-technical, the terrain has included steep (>60% grade) trail, off trail talus, slickrock, bog, stream, and river crossings, and the conditions have included snowfields, clay mud, ice, and sand. A good variety that includes just about everything that one might encounter in the Rockies with the exception of the “moondust” that typically develops later in the summer on some trails. The following is a summary of the differences, similarities, and superiorities between these two shoes.

In the end the two shoes compared in a way that a 911 might be compared to a GT3– both models are very high performance options, but one is much more “edgy” and tuned to a specific purpose whereas the other is a more widely usable and comfortable design with numerous advantages.

Note: 23 April 2015- I have posted an update on the performance of the S Lab X-Series at about 700 km (435 miles) of use here.


The S Lab X-Series shoe was announced last summer in Europe and the US and came as a bit of a surprise since Salomon have not ever played in the “road” shoe market but have, rather, focused on the trail shoe market. When this “road” shoe was introduced many cast a wary eye given Salomon’s lack of experience in this area. However, usually when Salomon does something they do it right and “different” than the competitors. And this holds true for the X-Series.

Salomon X series overall

Salomon S Lab X-Series

The S Lab Sense 4 Ultra is an evolutionary derivative of the  original Sense line brought out in 2012. As can be gleaned from the name of the shoe, Salomon are on the 4th generation of the Sense. In 2012 the shoe introduced super light weight, high traction, incredible proprioception, ultra-light ProFeel carbon fiber rock plate, some unique materials, and, most importantly, Endofit construction to the trail running world. The EndoFit construction has been universally acknowledged as a superior approach to fit and feel. The progression of the models since have fixed performance and durability issues primarily with added traction (more and deeper lugs) and new, more durable, materials and constructions. Such is the same with the latest iteration in the Sense 4. This shoe is the flagship of the Salomon trail running offerings but the model has become a bit “long in the tooth” since there have been no real advancements beyond those first introduced in 2012. It is expected that Salomon will disrupt the trail running market sometime soon with an all-new model, perhaps with a dose of the carbon technology that they have been applying to the cross country ski boot and mountaineering boot markets.


Salomon S Lab Sense 4 Ultra



The X-Series and Sense 4 both employ many of the same construction elements and materials- EndoFit, ProFeel film, SensiFit, and ContraGrip outsole. The differences lie in some of the materials in the upper, the amount of dual-density EVA incorporated, the design and attachment of the outsole wear layer, and the geometry of the shoe itself.

The X-Series offers a wider forefoot (about 3 mm on my size 7.5US, 40 2/3 EU) and a wider, squarer toebox. The heel is also wider by about 5 mm on these size 7.5US.

Salomon X series comparison forefoot

Toebox and forefoot area of S Lab Sense 4 Ultra (left) and S Lab X-Series (right) showing the wider, squarer toebox and a 3 mm wider forefoot dimension in the X-Series (size 7.5 US (40 2/3 EU)). The heel of the X-Series is also wider- by about 5 mm.

Perhaps a more significant difference is the midsole stack where the X-Series has a 19 mm heel/11 mm forefoot and the Sense 4 has 13 mm heel/9 mm forefoot stack. Both models use “dual-density” EVA where a cushier EVA can be placed where needed (I assume that the lower density, softer, EVA is in the forefoot and heel). The overall stack height (including the outsole) for the X-Series is 23 mm heel/15 mm forefoot giving an 8 mm drop. The Sense 4 adheres to the “low drop” Sense design ethos with a total stack height of 19 mm heel/ 15 mm forefoot and a 4 mm drop.

The outsole design is quite different as expected since the X-Series is intended for roads and “city trails” (whatever that means). The Sense 4 continues with the minimalist chevron array that has proven to provide outstanding performance in everything but ice and, to some extent, water crossings on submerged rocks. The X-Series outsole has a much larger surface area of contact but still with significant, deep lugs in strategic areas. The X-Series also has a segmented outsole wear layer that is glued on whereas the Sense 4 outsole wear layer is one piece. Salomon had durability issues in the original Sense model with such segmented wear layers coming off due to failure of the glue and the associated very long exposed glue-line. Hopefully they have since figured out a reliable and durable way to glue these segments.

Salomon X series outsole

Salomon S lab Sense 4 outsole

S Lab X-Series outsole (top) and Sense 4 outsole (bottom) showing large difference in traction design between the two models.

The X-Series also has a deep cutout extending from the middle of the outsole rearward into the heel area. It is not clear what this design feature is for but it may provide additional longitudinal stiffness through the middle of the outsole. Upon examination the X-Series is much stiffer longitudinally in this area than the Sense 4, although the forefoot stiffness is similar between the two models.

The X-series employs a significant “rocker” geometry, similar to that in the Hoka line of shoes. The Sense 4 retains the low, flat profile of past Sense models.

Salomon X series compared to Sense 4

Salomon S Lab X-Series (upper) and Salomon S Lab Sense 4 Ultra (lower) showing the substantial “rocker” geometry incorporated in the X-Series when compared to the Sense 4 Ultra.


The heel cups are similar but the ankle cups are different. The X-series has a symmetric ankle cup whereas the Sense 4 has an asymmetric set-up. I have felt no difference between the two while running, so it is not clear what the higher inner ankle cup does on the Sense 4 other than perhaps protecting a bit more in rocky conditions and from opposite side heel scuffing.

Salomon S Lab X-series back comparison

Rear view of the Salomon S Lab Sense 4 Ultra (left) and the Salomon S Lab X-Series (right) showing similar heel support structure but very different ankle cup configurations.


Salomon X Series ankle cup comparison

Ankle cup comparison showing Salomon S lab Sense 4 Ultra (top) and Salomon S Lab X-Series bottom. The Sense 4 has an asymmetrical cup whereas the X-Series is symmetric. The Sense 4 also has much more rear roll-over of the padding.


The upper materials are quite different where the Sense 4 utilizes the same (or similar) 3D fine mesh fabric throughout the upper with the heel wrapped in a tough solid polymer as seen in previous Sense models. The X-series uses primarily three different materials in the upper- a “barely there” mesh on the outside panel for ventilation, lightweight Lycra through the toe and forefoot region, and a beefier nylon fabric around the heel and throughout the inside are area up to the forefoot.

Salomon X Series side veiw

Salomon X series viewed from above

View from above of the Salomon S Lab X-Series showing a toebox and forefoot that is wider than that in the Sense 4 Ultra.



The s lab sense 4 uses the same (or similar) 3D mesh material as found in previous Sense models for the entire upper with the exception of the hard solid polymer around the heel.



View from above of the Salomon S Lab Sense 4 Ultra showing the slim and fast profile that is a fundamental part of the Sense line.

The polymer overlays look similar but they are actually very different. They both have the signature “zig-zag” side features but the X-Series toe area is much more pliable than the Sense 4. The Sense 4 overlay is much more structural and therefore the Sense 4 provides much more protection for toes than the X-Series. Both models have similar toe bumpers however as this is the most likely place that one will stub a toe.


The two models have very similar weights. The S Lab X-Series shoe is quoted as weighing in at 218 gms (7.7 oz) for a size 9 (US). My size 7.5 (US) (40 2/3 (EU)) tipped the scales at 215 gms (a little less than 7.6 oz). That is lighter than the quoted 238 gm for a size 9 (US) in the Sense 4 and the actual measurement of my Sense 4 Ultras in size 7.5 (US) at 227 gms.


The X-Series is $160 US and the Sense 4 Ultra is $170 US. Both are expensive shoes but if they last as long as other S Lab shoes I have used, the “pennies per mile” metric should make these shoes a reasonable offering from a price perspective.


RED! Salomon have simplified the graphics and the all-red X-Series are quite distinctive. No other colors are available in either model.

Running Performance Comparison

As outlined above I have tested these shoes on the same trails, conditions, and terrain. They have both seen about 200 miles (300 km) of use on buffed to mid-technical trails and terrain varying from steep (>60% grade) trail, off trail talus, slickrock, bog, stream, and river crossings. The conditions during testing have included snowfields, clay mud, ice, and sand. This is a variety that includes just about everything that one might encounter in the Rockies with the exception of the “moondust” that typically develops later in the summer on some trails.

General Running Characteristics

When comparing these two shoes the primary difference one will note at the outset is the cushioning and the “rocker” geometry of the X-Series. This makes the X-Series stand apart from the Sense 4 not only on the road but very much so on the trail. Proprioception is better in the Sense 4 but the X-Series has very good trail feel albeit with a bit of dampening.

The cushier ride of the X-Series is welcome, particularly to those used to the direct, somewhat hard ride of the Sense. While the Sense is likely to comparatively increase stride efficiency this comes at a cost of comfort and durability as it concerns ones feet. The X-Series provides a nice compromise between the “hardcore” trail feel of the Sense and the disconnected trail feel of a maximal shoe like a Hoka Stinson.

The X-Series also has a slightly larger total area outsole and much larger surface area of contact. One will feel this immediately as well and, just as such larger area outsoles do with the Hoka line, there is a perceptual “smoothing” of rocky trails in comparison to the Sense. Although I have yet to be on highly technical, fast running trails yet, I have not noticed a significant decrease in control between the Sense and the X-Series. The X-Series feels just as nimble as the Sense on typical buffed to mid-technical trails.

The larger, squarer toebox of the X-series is noticeable and in certain situations one can feel a bit more movement in the forefoot, particularly on steep downhills. I have run a couple of 3 mile ( 5 km) continuous steep (>15%) downhills in both models and found similar pace and feel except in the steepest (>50% grade) of areas where the X-Series begins to break loose where the Sense does not. The EndoFit is obviously doing a great job of helping one to maintain control in such challenging conditions and the ProFeel rockplate is doing an outstanding job protecting against sharp rocks.

In a couple of long (30+ km) runs on the same course the X-Series proved to be a very comfortable option when compared to the Sense 4. My feet were ready for some relief at about 32 km in the Sense 4, whereas, in the X-Series, I was looking forward to continuing on. That’s a big difference and one that will play a major role in a 50-100 km race.

Performance in Water, on Snow, and on Ice

One concern I had initially was that the Lycra upper of the X-Series would not drain after a water crossing as well as the 3D mesh of the Sense does. Not so, and, in fact, the X-Series is draining better in my experience.

More importantly, the X-Series performs much better on wet and/or slippery rocks. I found very good traction in stream crossings with the X-Series where the Sense would be somewhat unstable, particularly if any algae was present. The X-Series crosses rock-strewn streams with confidence and stability. This is most likely due to the simple physics of increased surface area for the ContraGrip when compared to the Sense- a lowered net shear stress for the X-Series allowing for significantly increased traction. I will update on performance in this condition once the summer algae thickens up on the submerged rocks.

A similar experience is found on snow and ice- the X-Series just plain outperforms the Sense on snowfields and ice. First, the increased traction helps establish control. Second, glissading is much smoother and controllable with X-Series as once static friction is overcome and gliding begins the larger surface area and less aggressive lugs allow for a “ski feel” and the associated control. Being a cross country skier helps but I was able to traverse a 200 m snowfield in one controllable glissade whereas in the Sense this same snowfield required three starts and stops due to “dig-ins” and lack of control. The same has been my experience on ice- the X-Series is much more stable on ice. Of course the Sense is particularly bad on ice but, with the X-Series, I was able to safely cross numerous “luge runs” of glare ice  that routinely  develop in the woods as winter fades and spring arrives. I would not even try to do these crossings with the Sense.

One outstanding question is how hot will the Lycra be; the material is thin and drains well but Lycra is not a particularly cool fabric in hot weather. Durability of the Lycra in abrasive conditions is another concern- time will tell.

Off Trail and Performance in Mud

I have taken the X-Series across some significant talus fields at running pace both up and down and have found very good performance, and, in some cases, better performance than the Sense which is already an outstanding performer on talus. Once again the source of the superior performance of the X-Series on talus is the increased dry traction when needing to make a big move on the talus field during descents. The larger surface area provides just that little bit more of a direction-changing force needed when heading directly for a large boulder or drop-off.

When crossing bogs I feel no difference between the models and the X-Series performs admirably right through the best muck and bramble that Idaho can offer. In pure mud, I was concerned that the big cutout in the outsole would just serve as a reservoir for mud and a large area for attachment of additional mud, particularly in clay-based mud. This did not happen and I find that the X-Series actually accumulates less mud than the Sense; not sure why. But as far as traction in pure mud on trail, the Sense 4 is superior; the widely spaced and aggressive lugs on the Sense 4 do a good job of piercing through the mud and hanging on to whatever grip is available whereas the X-Series tends to float a bit until one engages the outer, deep lugs. In practice this means that you will slide around a lot more in the X-series on mud so if you are regularly running in mud, the X-series would not be a good choice. My experience here in the Northern Rockies is that on the rare occasions when we do have significant sections of mud nothing seems to work very well (read the accounts, for example, of the 2014 Bear 100).

Concluding Comments

What I have found with the S Lab X-Series “road” shoe from Salomon is quite unexpected from what I thought the shoe would be. I expected a road shoe that could be used on buffed trails. The X-Series turns out to be an excellent, very nimble trail performer in a broad range of conditions even rivaling the outstanding performance of the Sense 4 in certain cases. This all comes with a nice dose of cushioning. Although I look forward to seeing how durable the outsole and upper is in long term use on muntainous trail conditions, it seems that Salomon may have hit an optimal mix of performance and comfort with the X-Series.

The S Lab Sense 4 Ultra continues with the outstanding, high performance, and “edgy” character of the Sense line giving unequaled proprioception and control on high speed trail downhills and all around performance for mountain running. The ride is “direct” and hard but efficient. It is also marginally comfortable at distances greater than about 50 km.

Bottom Line

Just as the 911 offers a nice mix of performance and comfort when compared to the “edgy’, stark, but super fast and controllable GT3, the S Lab X-Series does the same when compared to the S Lab Sense 4 Ultra. The Sense 4, like the GT3, has capabilities second to none in certain conditions, but this performance comes at a cost- long distance comfort. The X-Series offers a little less performance (and “egdy-ness”) in some cases and better performance in others, but a lot more comfort for the longer races and runs.

I’m going with the X-Series for my trail running going forward this season. And I am not the only one- Max King ran the LA Marthon in 2:17:30 in the X-Series, Justin Houck just won the 2015 Gorge Waterfalls 100k Montrail Cup Race, and Ellie Greenwood ran the Vancouver Marathon in 2:47 in the X-Series. Quite the versatile shoe!

I’ll keep you updated.

Embrace Your Conditions!

While studying at Oxford in the early 80’s I wanted to absorb a “full” experience during this English sojourn. So in addition to saturating into the academic life among the colleges, I sought out new athletic opportunities as well. After being “consoled out” of my college’s intramural rugby team by the coach (he feared for the life of a scrawny, 122 lb, American oblivious to the reality of rugby as a sport), I took to a lightweight crew and stumbled into an active Fell running community. The crew experience was great and provided much insight into the truly team nature of this sport (both on and off the water) and the rather elaborate traditions, but the Fell running proved to be much more of an experience for me.

My memories of the Fells were sparked when I saw the recently released African Attachment/Salomon video with Rickey Gates and a number of Fell running greats on Fell running in the Lake District:

The robust group of runners that I had the pleasure to run with for a couple of seasons made a significant impact not only on my running but also (and in a much greater way) on my perspective as it relates to truly experiencing a place.

The mantra of the group was: “Embrace your conditions!”. Independent of how raw and unwelcoming the conditions were (and “raw” and “unwelcoming” are mild versions of what one might regularly encounter in the Fells) we celebrated the visceral and intimate experience that would naturally materialize when one did not let the conditions become a barrier. It was new territory for me as previously I would typically limit a run or not run at all unless the conditions were at least palatable. But with the encouragement and peer pressure from the group I came to actually prefer the difficult conditions that were not infrequent in the Oxford area, the Cotswolds, the Peak District, and the Lake District where we ran.

This mindset and mantra has ever since informed how I try to approach life’s experiences- whatever the endeavor be it athletic, professional, or what have you. Rather than attempting to alter or otherwise modify the conditions that face one, this approach embraces what exists and challenges one to figure out how to make a way through, cover the ground, and finish- whether a run, a race, a project, or a relationship. This is not easy to do as we often fall into the mindset of “what could or should be” rather than making keen observations of “what is” and figuring out a way to go forward. Also, the forces at work can seem insurmountable- and many times they are. But this should not deter one from maintaining the mindset and moving forward, constantly re-evaluating what is the best path given the current circumstance. For me, it took many years before this approach became the default, but once in place what had previously appeared as insurmountable barriers became opportunities for optimization, challenges rather than burdens, and, in the end very valuable experiences.

So the next time you face a training run with a mix of rain and snow, deep muddy conditions, a driving wind, and low visibility think about “embracing your conditions”- you just might have a valuable experience upon which to draw in your next race when the inevitable unexpected happens.


Salomon SpikeCross Sense

With a low snow winter, lots of sunshine, warm temperatures, and an injured shoulder, running has materialized quite early this year. But this running comes with a significant challenge- icy conditions. Overnight lows in the teens and low 20’s F followed by 30-50 degree F sunny days produces glare ice conditions throughout our otherwise packed powder winter running trail system. This situation, in my experience, requires the use of metal spikes in or on running shoes.

As outlined previously with the Salomon SnowCross shoes, I have taken a pair of the Salomon SpikeCross shoes and turned them into a SpikeCross “Sense” by removing all of the heel lugs but leaving the 4 spikes in this area. The result is a lower drop version of the SpikeCross that, for those who prefer and use lower drop running shoes, really hits the mark for winter running on trails in icy conditions.


Salomon SpikeCross 3 before modification. These shoes were just sitting on a shelf not being used because the higher drop aggravates my Achilles tendon.


Salomon SpikeCross “Sense”: removal of the rear lugs drops the heel about 8-10 mm (the spikes just cut into the snow or dirt) making the overall drop about 5-7 mm. Note: the black rubber used on the SpikeCross proved to be a more formidable challenge for removal than the white rubber used on the SnowCross. Beyond a few choice words, removal is doable but difficult.

I now have in excess of 300 kms on these modified SpikeCross shoes and can report excellent results. No issues with the Achilles, exceptional grip on crusted snow and ice, and good performance on dirt.

Now, if only Salomon could see fit to bring out a Sense winter running shoe with spikes and an integrated gaiter…. in meantime these are working fine.

Salomon S Lab X-Series – Review – a nice addition to the S Lab group

I recently received a pair of Salomon S Lab X-Series a “new for 2015″ road shoe. As far back as I can remember, Salomon have never offered a road running shoe. And if they have offered a road shoe in the past, they certainly have not considered such shoes as a core part of the brand. So it was with a bit of apprehension that I slipped on the Salomon S Lab X-Series for some mixed miles of road and buffed trail. This apprehension soon evaporated into the unseasonably warm air here in the central Idaho mountains and was replaced by pure confidence in Salomon’s ability to enter the road shoe market.

Note: 3 April 2015- I have posted about a direct comparison of the X-series and the Sense 4 including a couple 100 miles (300 km) on each model both on trail and off-trail in a variety of conditions here.

Note:: 23 April 2015-  I have posted an update on the performance of the S Lab X-Series at about 700 km (435 miles) of use here.

Salomon X series overall

The Salomon S Lab X-Series- a road shoe from the trail experts.

The S Lab X-Series shoe is basically a road version of the Sense trail running shoe. What this means is that all of the fit technologies that make the Sense such a great trail shoe have been incorporated into the X-series along with a much cushier midsole and less aggressive outsole. The end result is outstanding.


The upper is constructed of materials and design that is expected for a road shoe that will not see much, if any, technical trail conditions. As such, the front portion of the upper is made of lycra with some side mesh panels on the outer side for ventilation. The rear portion of the upper and the inner side is made from a much beefier nylon as expected and needed for proper heel structure and protection from opposite shoe heel scuffing. The design includes no toe protection other than a small front bumper- you do not want to stub your toe on a rock in these shoes.

Salomon X Series side veiw


Th interior of the shoe incorporates the Endofit construction as is utilized in the S Lab Sense line of trail running shoes. This feature has received uniform rave reviews and general acceptance as a superior design element in current running shoes. The Endofit approach produces a secure yet very comfortable fit via an inner “sock”. This fit is often described as “slipper-like” and I concur.

Another feature to note is that the ankle cup topology is symmetric, meaning that the curved cup is the same on both the inner and outer sides. This is not the case for the Sense where the inner cup is taller than the outer cup as will be shown below.

Salomon x series ankle cup

Symmetric ankle cup in the Salomon S Lab X-Series.

The polymer overlay reinforcements take the familiar zig-zag shape but also wrap around the toe area for some minimal protection. The toe box is substantially wider than that in the Sense trail shoe line as will also be shown later.

Salomon X series viewed from above

View from above of the Salomon S Lab X-Series showing a toebox and forefoot that is wider than that in the Sense 4 Ultra.


Perhaps one of the most differentiated features of this shoe to the Sense line is the EVA cushioning. On Salomon’s 1-5 scale of “cushion” in their technical literature, the Sense 4 Ultra ranks at “1” whereas the X-Series is rated “5” where a larger number indicates more cushioning. This difference can be seen in the reported midsole thicknesses where the X-Series has a 19 mm heel and 11 mm forefoot EVA thickness whilst the Sense 4 Ultra has 13 mm heel and 9 mm forefoot thicknesses. So 6 mm more EVA at the heel and 2 mm more in the forefoot. Both models use the cushier “dual density” EVA construction (where a cushier EVA is strategically placed in a matrix of a less cushy formulation).

The X-Series also uses the ProFeel film technology developed for the Sense series shoes so there is good protection from rocks if one uses this shoe on trails.


The outsole of the X-Series is a hybrid trail/road configuration that combines some deep lugs asymmetrically with smoother areas of a design similar to other lightweight road shoes. Salomon claims that this design allows for both good grip on flat paved surfaces (wet or dry) as well as non-technical trails. There is also a deep cutout extending from the midsole into the heel region, which is likely a weight saving feature but may also provide additional longitudinal rigidity.

Salomon X series outsole

Outsole of the Salomon S Lab X-Series showing asymmetric tread pattern and deep lugs toward the outer portion of the forefoot. The wear layer is glued in numerous pieces to the EVA midsole, something which has proven to be problematic in the past- time will tell.

The outsole utilizes Salomon’s proprietary “Contragrip” polymer compound that has been in use on many Salomon models over the past few years. The wear layer is glued to the EVA midsole in segments much like the original Sense model of 2012. This gluing proved troublesome as the individual segments had a tendency to peel off and thereby limited the life of an otherwise sound shoe. Salomon seemed to fix this problem in the Sense 2 but went to a single molded piece in the Sense 3 (and 4). The single piece construction limits the linear area of exposed glue lines and seems to be a better choice for durability. Perhaps Salomon have figured out how to reliably use the segmented design but I will be casting a wary eye as I put miles on the X-Series.

Salomon S lab Sense 4 outsole

Salomon S lab Sense 4 Ultra outsole showing the single piece wear layer construction.

Running Geometry

The overall construction of the shoe has a significant “rocker” geometry similar to that found on many other trail and road shoes, and particularly on the Hoka line. The rocker geometry is said to better enable a forefoot strike when combined with a low drop. Many have noted favorably how well this has been executed on some of the Hoka models.

Salomon X seies side view

Side view of the Salomon S Lab X-Series showing the significant “rocker” element in the forefoot.

The drop of the X-Series is quoted as 8 mm with total stck heights of 23 mm heel and 15 mm forefoot. This drop is something of a hybrid between a “traditional” high heeled road shoe and a low drop trail shoe. I would prefer a lower drop but will defer judgement until I accumulate a significant volume of miles on the shoe.


The S Lab X-Series shoe is quoted as weighing in at 218 gms (7.7 oz) for a size 9 (US). My size 7.5 (US) (40 2/3 (EU)) tipped the scales at 215 gms (a little less than 7.6 oz). That is lighter than the quoted 238 gm for a size 9 (US) in the Sense 4 and the actual measurement of my Sense 4 Ultras in size 7.5 (US) at 227 gms, so a light shoe indeed. This is a good thing as weight matters- a lot, particularly for lighter weight (sub 125 lbs) runners like me.

Comparisons with S Lab Sense 4 Ultra

Since many of those who currently use the S Lab Sense shoe are likely to consider this shoe for road (and buffed trail) use, a comparison of the significant differences with the current Sense 4 Ultra model are presented below. The first comparison shows the larger toebox and forefoot area.

Salomon X series comparison forefoot

Comparison of the forefoot area of the Salomon S Lab Sense 4 Ultra (left) and the Salomon S Lab X-Series (right). Both the toebox and the forefoot width are larger.

A second comparison shows the substantial “rocker” geometry compared to the Sense 4 Ultra.

Salomon X series compared to Sense 4

Salomon S Lab X-Series (upper) and Salomon S Lab Sense 4 Ultra (lower) showing the substantial “rocker” geometry incorporated in the X-Series when compared to the Sense 4 Ultra.

A third comparison shows how similar the heel cup support structure is on both shoes.

Salomon S Lab X-series back comparison

Rear view of the Salomon S Lab Sense 4 Ultra (left) and the Salomon S Lab X-Series (right) showing similar heel support structure but very different ankle cup configurations.

However the ankle cup area is quite different with the X-Series having an symmetric cutout design whereas the Sense 4 Ultra has an asymmetric design and more rear roll-over in the padding.

Salomon X Series ankle cup comparison

Ankle cup comparison showing Salomon S lab Sense 4 Ultra (top) and Salomon S Lab X-Series bottom. The Sense 4 has an asymmetrical cup whereas the X-Series is symmetric. The Sense 4 also has much more rear roll-over of the padding.

Initial Running Impressions

I have had the X-Series shoe out for about 50 km of mixed use- about 30 km of road and 20 km of buffed trails. If you are a S Lab Sense user, you will note that the fit is very much like the very comfortable “slipper”-like feel of the Sense 3 and 4. The X-series is comfortable from the outset and I have noted no change in these first 50 kms. Also, if you are a Sense user you will immediately notice the “rocker” geometry and the way the shoe subtly prods your posture forward and on to the forefoot. I found this to be a nice feature of the Hoka Stinson trail shoe particularly given the maximal cushioning of that shoe. With the highly cushioned shoes there is the reality that when the cushion is deformed and your foot forms deep into this deformation one must overcome the not insignificant physical barrier thus created. The “rocker” geometry does a good job of dealing with this. And so it is also with the X-Series which has a much more padded midsole when compared to the Sense 4 Ultra.

Continuing with this, the second thing one will notice is the substantially greater cushion when compared to the Sense 3 and 4. On road surfaces this added cushioning is very apparent and quite welcome. It almost makes one want to actually consider running on roads from time to time (heresy!). On the trail the difference is not really noticeable although I have not taken the shoes on any technical and rocky stretches yet. Stay tuned.

I really like the feel of these shoes while running. The combination of fit, cushioning, geometry, traction, and weight seem to provide a near optimum balance between comfort and efficiency on roads. As far as trails, I will be giving these shoes a full workout once the snow recedes in the next few weeks. Based on these initial impressions, I think that this shoe will be a nice option to have available in ultra races where there is a lot of dirt road and/or buffed trail. I am likely to put these into a drop bag at an aid station in a 100 km race this year where the last 13 miles are a downhill charge into town on graded dirt roads. The cushioning and rocker geometry will be just the ticket!


$160 US. Steep but if these shoes last as long as the other S Lab shoes I have used then the “cents per mile metric” will be more than palatable. Only time will tell.

Bottom Line

A very nice entry by Salomon into the road shoe arena with all expectations that this shoe will be an outstanding performer- stay tuned.

“Miracle on Snow” – Falun Diary: Women’s 10 km FS World Championship – luck of the draw and hard efforts

The unexpected silver and bronze medals for US cross country skiers Diggins and Gregg, respectively, in the 10 km freestyle race at the recent Cross Country Skiing World Championships in Falun Sweden has raised eyebrows and fueled much discussion both in the US and among others in the global cross country skiing community. Much of the discourse has centered on the effects of dramatically changing weather conditions on the ski speed of the later starters in this interval start race.


The (relative) poor performance of favorites Bjoergen (bib 65) and Johaug (bib 63) (both of Norway) who started in the last group of seeded skiers has been put forth by some as evidence that the deteriorating conditions played a dominating role in the final results. Others point to the winner, Kalla (bib 49) (of Sweden), who started just seven minutes before Johaug and and eight minutes before Bjoergen as support that start time was not deterministic for performance. Presented here are a few observations on and analysis of various available data types for the race as it played out.


Diggins (bib 37) started 13 minutes before and Gregg (bib 3, in the first group of unseeded skiers) started 30 minutes before Johaug (bib 63). Review of the video of the race and other on-the ground reports reveals that at the start the conditions were 1.1 C air temperature, -0.4 C snow temperature, 86% humidity, and overcast with no actively falling snow. At about 5 minutes after the start of the first skier, light snow was falling (starting at about bib 10), at 10 minutes a rain-snow mix was coming down (about bib 20), and by 20 minutes into the start it was snowing heavily with very wet (free water) conditions (starting at about bib 40 onward). A significant layer of heavy wet snow had accumulated on course by about 30 minutes into the start order (bib 62).

The winning time was 25:08.8. A simple calculation of percentage of skiing time spent with an accumulated heavy, wet snow layer on course shows that Weng (of Norway, another favorite), Johaug, and Bjoergen all spent about 100% of their skiing time in these conditions whereas Kalla spent about 85% of her skiing time, Diggins about 50% of her skiing time, and Gregg about 0% of her skiing time battling the adverse ski track conditions.

All who ski regularly and/or in circumstances where the conditions are changing to heavy, wet snow accumulations know how drastically ski speed is depleted from an otherwise optimized ski flex/grind/structure/wax for non-actively snowing, high humidity conditions. I have personally measured diminished ski speed well in excess of 10% in tests after such accumulating wet snow conditions prevailed. Although wax will play a relatively minor role, ski flex and grind are particularly critical to attaining ski speed in the conditions facing the late starters in this race. So if the late skiers had selected their skis based on conditions at the start of the race, they likely had skis with less aggressive grinds and stiffer forward flex. Such a selection would lead to ski speeds many percentage points slower than skis optimized for skiing through heavy, wet accumulations. That Norway made an errant selection for skis is supported by remarks of their skiers in the race who have been quoted as saying that “our skis were ass”- which is apparently Norwegian-speak for “our skis sucked”.

It is not difficult to anecdotally explain the unexpected results from this race based on the analysis above. Johaug and Bjoergen both finished about 9-10% back from the winning time. Given that Kalla had about 15% of her skiing time with less challenging conditions, one can staightforwardly account for about 1.5-3% of the 9%-10% deficit in finishing time using a linear function for decline in speed with conditions*. That still leaves a hefty 6% or so of deficit to account for. Using prior performance as a guide, it is clear that both Johaug and Bjoergen should have been much closer to Kalla and it is possible that after being given increasingly positive splits off Kalla (not to mention off of Diggins and Gregg as well) there may well have been a “limit losses” posture taken by the athletes to ensure their performances under better conditions later in the week. Kalla also likely had a very good day.

In the case of Diggins, she finished about 3% back of Kalla and about 6% in front of Johaug and Bjoergen. Once again using a linear approximation, just about all of that 6% could be accounted for based on the difference in skiing time in the difficult conditions (50% for Diggins and 100% for Johaug and Bjoergen). Obviously one can account for all of the difference (and more) between Gregg and the Norwegians with the same reasoning.

Next let’s take a look at the splits at 1.5 km into the race, at a point where the wet snow accumulations for the late starters were still manageable. At this checkpoint the following are the splits:

1. Kalla 3:51.0

2. Johaug 3:59.

3. Niskanen 4:02.4

4. Jacobsen 4:02.8

5. Bjoergen 4:03.0

15. Diggins 4:08.7

20. Gregg 4:09.2

This sequence looks “normal”, i.e. it is what would be expected (except that Bjoergen and Johaug would not be so far behind so early). Things unraveled from here as the wet snow accumulated. Johaug dropped from 2nd at 1.5 km to 26th at 5 km, similarly Bjoergen dropped from 5th to 32nd. Unheard of, but let’s also take a look at some more analytical data and at how astonishingly different this race is when compared to other, similar races held in more constant conditions.

One of the basic expected functionalities in timed event athletic endeavor is that history is a very good guide for expectations of performance in individual events. This holds true for cross country skiing just as it does in track and road running, cycling, and numerous other sports. The basic premise: past performance is highly correlated with performance for a given event.

Presented below is a plot of the FIS Distance Points (as of the race start) versus percentage back from the winning time. Only those competitors who have finishing times within about 10% of the winning time are included in the cohort as these athletes represent the “elite” population in the race. FIS Distance Points are an acceptable surrogate for an historic performance metric for the current season. It is expected that such a plot would yield a high positive slope as past performance (FIS Distance Points) is a good predictor for individual race performance. Application of a simple linear model to the data shows that there is essentially no correlation whatsoever of finishing time to FIS Distance Points for the Women’s 10 km FS World Championship race. A highly unexpected result- an ink splatter, a sneeze!Slide1

Now let’s take a look at the same type of data for another, typical, interval start race from the 2014-2015 season. In this case we use the Davos Women’s 10 km CL interval start race from December. Presented below is the same plot as above but with the data from the Davos race also plotted (in green). The equations for the fitted linear models are shown on the graph. Note the high positive slope of the fitted line and high (greater than 40%) correlation between FIS Distance Points and finishing time for this race (note: Bjoergen won this race with Fessel (GER) 2nd and 1.3% back, Weng 3rd, Haga (NOR) 4th, Nystad (GER) 5th, and Johaug 6th- Diggins was 27th and 6% back and Gregg finished this race in second to last place, over 16% back (and therefore is not a part of the analyzed elite population)).


The Davos race is exemplary of what is normally seen with such cross country races. In fact, of the 20 or so races that I have analyzed from the past couple of seasons, the correlation was positive in all cases and had R^2 values from about 0.38 to 0.60. For instance presented below is the data for the Women’s World Championship Skiathlon a couple of days before the 10 km CL race showing a similarly positive slope and high correlation.


Bottom Line

The lack of any correlation with FIS Distance Points as seen in the Women’s 10 km CL World Championship race sets this race apart as not “normal” nor even fathomable from a performance perspective. Clearly the conditions played a primary, controlling role in the outcome. Ski flex and grind/structure choices (not wax) were dynamic during the race and the Norwegians likely screwed this up. At the same time Kalla likely made a good ski choice and also had an outstanding day. Diggins and Gregg benefited greatly from start time and this combined with hard efforts lead to their surprising results.

In the end a race is a race (even if it is interval start and the weather goes wacky) and a World Championship medal stands as a significant achievement. Congratulations are well placed with Kalla and the US skiers. However this race will forever have an asterisk and will not be a good source for prediction of future performances.



*From a physics perspective it is not difficult to argue that ski speed is actually non-linearly affected, i.e. the faster the speed the higher the percentage declination in speed. So in a sport where winning times are often only tenths of a percentages faster than other skiers, the increased percentage speed declines for faster skiers is even more impactful than for the slower skiers.

Pikes Peak Marathon – a race of two dominant performers

The Pikes Peak Marathon and Ascent race has a long history having been first run in 1936 and then continuously since 1956 to the present. The race is an iconic “mountain” event and has been run by many high-level competitors over the years. It is also a “bucket list” race for many. I had focused training on the 1979 edition when I was living in New Mexico but a road cycling team invite scuttled those plans as I would be only cycling and traveling for the entire summer. As a climbing specialist then, and now, I still have plans to do the race, perhaps even this year.

The 7815 foot (2382 m) 13.1 mile Ascent followed by a return route down the same trail makes the Marathon an “ultramarathon” as the fastest finishing times are about the same as that for some of the faster 50 km trail races. The race regularly draws top talent from the mountain and ultramarathon running world as well some washed-up elite and sub-elite road marathoners looking for a new challenge. In 2014 the Ascent race (run the day before the Marathon) was the designated World Long Distance Mountain Running Championship of the World Mountain Running Association (WMRA). Since 1976 the race has been run on the same course. This allows for performances in this time period to be directly compared and aggregated for analysis.

Even though the race has a long history and has been run by thousands including a fair share of international elite runners, the best results are dominated by two performers- Matt Carpenter and Ricardo Mejia. Carpenter has completed the race 14 times and won it 12 times and Mejia has run 6 times and won it 5 times (I could not find any data on possible DNFs). These two competitors also account for 6 of the 11 performances that are within 10% of the record time as well as the record time (by Carpenter). Carpenter has played a central role in the race for many years and has taken it upon himself to provide a resource for all things “Pikes” at his website Pikes Peak Central. The website provides a comprehensive collection of data, history, and advice on running the race- either the Ascent, the Marathon, both, or both in the same year (known as a “double”) as Carpenter has done a couple of times. A “double” is possible since the Ascent is run on Saturday and the Marathon on Sunday. After Carpenter’s 6 in a row winning streak from 2006-20011, the winners have been international since (Jornet 2012, Miahara 2013, Lauenstein 2014).

The record for the Marathon is held by Carpenter- set in 1993 with a super-human time of 3:16:39. No one has come within 2.5% of this time and this result stands as one of the greatest fixed course mountain running performances ever. There are only four other performances that are within 5% of the record and 11 that are within 10%, an impressive record given the thousands of national and international elite mountain runners that have competed in the race over the years.


In a previous post, the Pikes Peak Marathon was compared to a number of other (mostly ultramarathon) races to gain an understanding of competitiveness in such long trail running races. The results indicate that Pikes exhibits a very wide range of competitiveness including both exponential and linear finishing time distributions. The “linear” years have competitiveness indices similar to other very competitive races. The “exponential” years have competitiveness indices ranging from values as high as some of the most competitive road marathons to as low as some of the least competitive ultramarathons. The competitiveness calculations utilize the 125% cohort from each year of the event. The 125% cohort is chosen because it allows for comparison of events ranging from 10 km road races to 100 mile trail ultramarathon races. Although a “true” elite population would be best described as those competitors within about 10% of the winning (or record) time, the 125% cohort allows for inclusion of enough ultramarathon results to allow for statistical significance in comparisons. In addition, because of the magnitude of multiplicative pace differentials, the finishing times are naturally more spread out in ultramarathons than for similar pace differentials in shorter races such as marathons and other shorter road races.

Examples of typical “exponential” and “linear” competitiveness plots for the Pikes Peak Marathon are presented below for the 2009 and 2010 Men’s events. Carpenter won both of these races, in 3:37:02 and 3:51:54, respectively. The 2010 event had a much deeper field (20 competitors in the 125% cohort) than the 2009 event (14 competitors in the 125% cohort) something that is partly due to the slower winning time in 2010, although there are likely other contributing factors (e.g. weather).



Presented below are the competitive indices (CI), coefficients of determination, sizes of the 125% cohort, winning times, winners, and winners age for the Men’s Pikes Peak Marathon from 1976-2014. As noted above, this event period is chosen because the race has been on the same course for the entire time and allows for direct comparisons of finishing times and other, derived, metrics.


Pikes Peak Parametrics Summary all years cropped

Competitiveness index (CI), coefficient of determination, size of the 125% cohort, winning time, winner, and winner age for the Men’s Pikes Peak Marathon 1976-2014. The red CI values are for the highly competitive “linear” years.

Within this dataset of 39 competitions, we see 5 highly competitive “linear” years, 6 very competitive “exponential” years (CI>0.130), and quite a number of years (16) with low competitiveness (CI<0.110). Clearly the competitive fields at Pikes are highly variable but can be very competitive. This is not unexpected from a niche event which draws from a relatively small population of competitive runners.

Pikes Peak Marathon and Age

In long events like marathons and ultramarathons the optimal age for top competitors tends to favor an older runner than for the shorter events such as the mile. In another post, an analysis of the optimal age for competition in the road Marathon was presented. What is found is that there exists evidence that the top road Marathon competitors are getting younger, particularly since the 2008 Olympics where 21 year old Samuel Wanjiru won the gold medal. It is hypothesized that Wanjiru’s result has spurred on many more younger athletes to pursue the marathon at a younger age than has typically been observed. A plot of the competitor age on race day versus the percentage back from the record Marathon time for the top 2500 Marathon times is presented below and shows the current optimal age to be about 30 years. There is a “bulge” in the data on the young side of the “whorl” centered on about 30 years, indicating that there is something of additional interest in the dataset.


Pursuant to understanding this “bulge” in the data, a more granular look dividing the data into two time periods (1967-2008 and 2009-2014) presented below, shows that as of about 2009, the best results in the marathon are getting faster and that the average competitor age of these fast results is tending to a younger age. This supports the “Wanjiru” effect but does not confirm it.


Looking at the same type of data for Pikes Peak Marathon shows a similar optimal age of about 30 years, but with a diffuse indication of increased performance for older competitors. In this graph the red points are Carpenter’s results, the green points are Mejia’s results, and the yellow points are Waquie’s results. Guidelines are included to help the eye detect the lack of symmetry in the data (similar to those provided in the Marathon graph above). Even removing the outlier results of Carpenter in his winning streak as he entered his 40’s, there is still a trend toward older competitors having superior times to younger competitors.


Age on race day versus percentage back from the record time for the Pikes Peak Marathon 1976-2014 for the 125% cohort of performances. The red points are Matt Carpenter’s performances, the green points are Ricard Mejia’s performances, and the orange points are Al Waquie’s performances. Even with removal of the outlier results of Carpenter in his 40’s, there is a tendency for older competitors to perform better than younger competitors.


So the Pikes Peak Marathon may be a race for the older competitor, at least when compared to the road Marathon. It is not unusual that an event that involves such a high level of endurance along with a high reliance on slow twitch muscle fibers (type I and to some extent type IIa) would favor the older athlete. What is interesting with Pikes however, is that the downhill is run at a very high speed where utilization of fast twitch (type IIb) muscle fibers is important. It may be that the uphill part of the race dominates the skillset needed to be competitive, although it is usually the case that a fast descent is required for a win- something that reinforces the subtitle of this blog- “the race is made on the ups and won on the downs”….. and also something to consider if one should be attempting to put up a good time at this event.


Analysis of finishing time data for the Pikes Peak Marathon over the period 1976-2014 reveals the following:

  1. The best performances have been dominated by two individuals- Matt Carpenter and Ricardo Mejia.
  2. The competitiveness of the race is highly variable- the competitiveness indices can be as high as some of the most competitive road marathons to as low as some of the least competitive ultramarathons.
  3. Analysis of the age distribution within the 125% cohort for all time performance indicates that the race favors an older competitor when compared to the road Marathon.
  4. It is pointed out that even though the ascent portion of the race likely dominates the skillset needed for high performance, a fast decent is required for a good time. This appears to necessitate that top competitors have an unusual mix of slow and fast twitch muscle fiber development.