UKC

Lots of climbers seem to be obsessed with rubber hardness, talking about 5.10s stealth or talking about vibrams XS range claiming one is better than the other or talking about how they can feel the diffrence. I've just finished a course all about rubber manufacturing which seems to be a dark art in its own right and it got me thinking about our brands and how much they big up the rubbers they use.

Vibram catalogue quotes a shore hardness of 78 +/- 3 for xs Edge which would mean the range is 75-61 Sh/A. They quote a range of 74+/-3 for grip 2 which would be a range of 71-77 Sh/A.

That means that there is a good chance batch to batch shoe to shoe that if you had a pair of of say an instinct VS and an instinct VSR there is a likleyhood that the "stickiness" may overlap or even the marketed "harder" rubber may indeed be softer than the "stickier" rubber ! 

This ties in with what I heard Nathan from scarpa say on a podcast. Apparently scarpa frequently change the rubbers on athletes shoes without them knowing to see if they report a change in performance, but none of them ever notice.

This entire stickiness thing is starting to look a bit dubious !

What's more interesting is even taking this hardness measurement is difficult. As the rubber is tested it has a tendency to "relax" and softens and therefore the hardness isn't consistent through the measurement. I'm curious if this relaxation mechanism is why our feet tend to feel they are slipping when stood on a foot hold for too long?

Also another thing I've been told is that coloured rubber is often less sticky as its not as "pure" but after realising how much components make up commercial rubber I'm a bit doubtful.

If there are any rubber manufacturers on here I'd be keen to hear from you ? Also what type of rubber is vibram XS series? I'm assuming it's similar to car tyres and is a blend of multiple.

In reply to Aled Williams:

Very interesting. 

I've been wearing Instinct VSs and VSRs for years, with three pairs of the former and two pairs of the latter. One pair of each on its first sole, one pair of each on its second sole and one pair of each on its third. All resoles by Torquil (LLanberis Resoles) who is a Scarpa approved resoler. At similar levels of wear I can't tell the difference between VSs and VSRs, something that sunk in over time. I was either told in a climbing gear shop or read on the Scarpa website that you will only tell the difference in hardness/softness between the two after a while when the rubber on the VSRs soften but I have never noticed that.

Re rolling off holds, for me that increases when the shoe gets more worn and baggier: does not feel anything to do with stickiness of rubber.

To me the key thing about rubber stickiness is how clean the rubber is, which I am pretty sure is the crucial difference. All this money on sticky rubber but even if you start off with really clean shoes they soon pick up dirt and chalk as you climb.  

In reply to Aled Williams:

That's very funny. Do you have a link to the podcast?

I've never noticed a difference between shoe rubber from different manufacturers, but I assumed that was just because I have terrible footwork. Never tried a variety of brands on the same problem to compare though.

In reply to Aled Williams:

The differences is rubber will vary on temperature etc and unless using them right on the limits of coefficient of friction, with all other factors being equal mortals and even climbing gods often won't notice a difference. Basics still apply, harder rubber will edge better, softer compounds smear, so it's often impossible to compare anyway, because a shoes performance could vary from one pitch to the next. No rubber is actually stickie, the softer the rubber the more they deform around a rough surface increasing surface area in contact, thus more grip less slip.  

https://www.climbingshoereview.com/climbing-shoe-rubber-comparison/

In reply to Fellover:

It's the podcast on  careless talk (Aidan Roberts and Sam prior's show) I think his name is Nathan Hoette

In reply to Aled Williams:

That's interesting, I can understand the potential for overlap between one manufacturer's rubbers and it being difficult to discern the difference. However, between brands, I think the differences can be clearer. On a recent indoor problem with a small chip foothold, there was a distinct difference between the rubber on a resole from Torquil/LLanberis and a relatively fresh 'branded' rubber. The former allowed me to stand on what was a tiny rounded chip, the latter not... Usually, I'm oblivious to such differences - I guess the footholds I typically use are too big for it to be apparent!

In reply to ExiledScot:

Agree with temperature relation to hardness but the testing is carried out to a defined standard that stipulates a standard temprature.

Thanks for that article link but it dosent really compare the rubbers showing each ones shore hardness (I don't think this data is actually readily available from what I understood on the course and brands may have to sign NDA with their rubber compounded)

The experiment in the article on the surface seems good with relation to climbing but ultimatley does not control ageing, temperature, or rate of tilt which would be part of the time under tension. As rubbers soften as they are subjected to a constant force as part of the stress relaxation, mesuring the time would be really important. What that might mean is that initially the rubber is least "sticky" and softens if held at a constant force and angle getting stickier but potentially if held at the angle and force for long enough would just slip off regardless from stress relaxation and becoming too soft ? (That's what I understand anyway..)

Also shear forces on rubber make it more viscous so this would play a role too

All very complicated i think we need a materials engineer on this forum !

In reply to Aled Williams:

Ageing is another thing I've not mentioned, hardness values are on fresh runner batches, who knows how long the rubber sat on the shelf at say vibram ? 

Does softer rubber age faster than harder rubber ?

Also would worn rubber oxidise faster due to increased surface area ? so would used shoes degrade faster than not used shoes ? 

Also could storing them in plastic boxes and exposing them to plasticisers and other chemicals make then ages faster without us realising ? 

So many questions ...

Rubber stickiness is a myth

In reply to Aled Williams:

I think a lot of the manufacturers talk is irrelevant for 90+% of climbers, it's like the boy racers putting the best low profile soft compound pirelli tyres on their 1.2 Corsa, might look good in the eye of the beholder, but performance difference is negligible. 

In reply to Aled Williams:

Contrary to Eric, I’ve got instinct laces and the difference between edge and grip is hugely noticeable. The stiffness of the edge rubber makes a difference to the overall stiffness of the shoe. 

In reply to Arms Cliff:

Out of curiosity though what are the shoes you own that have grip rubber ? The instinct lace (mens/orange) is a more stiff shoe by default than say a VSR 

The construction is diffrent with a illga (I think that's how it's spelt) wrap around the toe and I think has a slightly bigger midsole insert in the front. So it raises the question is it stiffer because of construction or the rubber? The wmns instinct lace has grip but apparently its still pretty stiff but won't really be comparable as the volume is diffrent that may change toe angle too, both contributing to overall stiffness. 

Also size makes a diffrence

In reply to Aled Williams:

Orange Instinct lace and low volume (teal) lace. Very similar on the foot (got different sizes to allow for change in volume). Have also had Velcro blue and Orange with difference still being very noticeable, particularly on small ‘picky’ footholds. Also find edge way worse on larger low friction feet (polished lime or volcanics eg) due to the lack of malleability. 

In reply to Aled Williams:

Having just come back to climbing after nearly a decade off I've dug a couple of interesting datapoints on aging out of my loft. My 5.10 slippers that are probably 13-15yo, threadbare and had long been relegated to beach/swimming duty are still lovely and soft and sticky, the rubber feels better than new. By contrast my put away new 8-9 years ago Sportivas are dry, hard and stiff as a board. They are by design a much more structured shoe with supported edges, thicker rubber soles and of course not all beaten to hell so it's not an apples and apples situation but the difference in the rubber alone is night and day. I suspect the Sportivas will improve as fresher rubber is exposed and the uppers break in allowing more compliance.

Sadly the 5.10s are back into the pottering and swimming pile as my left toes are now poking out of them

jk

In reply to Aled Williams:

My own personal conspiracy/hot take is that we're being marketed softer rubber than we need a lot of the time. I'm fairly light (65kg max) and I seem to chew through xs grip2 fairly quickly, it rolls off edges and gets torn by sharp textured rock. Granted I climb sharp limestone in a hot climate, but even when I climbed sandstone almost exclusively I found harder rubber felt more trustworthy underfoot, unless it was a giant slopey feature where arguably anything would work anyway!

Make XS Edge great again!

In reply to tomdiddlybomb:

Yeah, I agree with all that. I am heavier - 72-74kg or so. I have some very old miuras (rubber? dunno) but it's quite hard and fine for everything. Also some vapours that started as xs edge, wore out then resoled in xs grip2....and they have worn out in half the time. And have I turned into a smeary comp problem destroyer with the softer rubber?... no. Do they smear better?.. maybe, but it's hard to tell as the once stiff shoes have gone soft anyway.  I think I will stick to xs edge or whatever other manufacturers' equivalent is.

In reply to tomdiddlybomb:

What we need is some testing done with different masses and different temperatures - it might be that size 46 rockshoes need a stiffer rubber than size 36, due to the likely heavier climber wearing the bigger shoes.   It might be that someone climbing in tropical Thailand needs harder rubber than someone in the Peak in January.

In reply to Toerag:

Stiffness is deffo affected by the shoe size, as you don’t get a thicker midsole in a bigger shoe, or thicker rubber, so you’re naturally going to get more deflection. Works at the other end too, some ‘soft’ boots in very small sizes feel like B3’s when you try and bend them!

In reply to Toerag: But that's already effectively done.  Scarpa have models where the 'womens' model is in grip, the mens is in edge to account for the weight, plus the fact that a mans shoe is normally larger, and thus more flexible.

So apart from rubber softness, things that will affect it's behavious 'in the wild' are obviously weather/temp, thickness, amount of support from the midsole and construction and I'm sure you can add to the list.

Is it a conspiracy - no.  But like so many things a simple problem has a complex answer

What's the temperature those softness numbers quoted are measured at.? Shoes will have an optimum use temperature I guess.... 

In reply to ExiledScot:

That's not true.

Try taking a good pair of stickies, washing them carefully with warm water and washing up liquid.  Dry.  Squeak together.

A good chance the stickiness will support the weight of one shoe

In reply to Aled Williams:

Back in the '80s/'90s, it was widely rumoured (possibly even so far as an open secret), that most competition climbers were all using the same rubber (I forget which one, maybe Boreal). Climbers sponsored by other brands were (the rumour said) sending their shoes off anonymously to be re-soled with it.

In reply to ExiledScot:

It used to be the case (when I started climbing back in the '80s), that if you were prioritizing edging performance (e.g. for limestone), you'd buy board lasted shoes, which were stiffer and if you were prioritizing smearing (e.g. for grit stone), you'd buy slip lasted shoes, which were more flexible.

Then board lasted ones went out of fashion and I'm not sure if anyone makes them anymore.

Also, a brand new pair of shoes should edge better than an old, worn pair and vice-versa for smearing.

In reply to Moacs:

Saying it's sticky implies it's like glue, as said it deforms under pressure to increase it's coefficient of friction. 

https://www.climbing.com/gear/the-science-of-climbing-shoe-sticky-rubber/

In reply to ExiledScot:

Yes, exactly like glue, coefficient of friction >1.  That is why "sticky" rubber revolutionised climbing in the 80s

In reply to ExiledScot:

Thats a really good article cheers.

It got me thinking with all this non-newtonian and strain induced crystallisation, if you cut loose and stick your feet back on immediately im guessing the rubber will be at its hardest (least sticky) when the feet impact the wall ? If so it gives me another excuse hahhaha

In reply to Aled Williams:

Regarding the +/- tolerance of the rubber hardness and the rubber and the rubber types overlapping between batches. There are a few questions here, what's the distribution shape of the batch tests? Are we talking about a very steep even bell curve, a biased bell curve with a few outliers from each type overlapping in the middle, a very broad shallow curve with significant variation and overlap.

You could equally say that between batches  you could get the two ends of the distributions and get one very hard batch and one very soft batch increasing the difference between types and accentuating the difference.

Most people never clean their climbing shoes so debating the types of rubber they use is a waste of time. I sometimes give mine a good scrub with a nail brush and a bit of soap and the difference is really very noticeable, even at my punterific grade. Should do it more often really.

In reply to Aled Williams:

How many standard deviations are the +/- figures based on?

In reply to Aled Williams:

My feeling re: sensation of rolling off, is that is more about shoe construction (e.g. midsole being soft or stiff) and body tension than anything. A shoe doesn't "roll" off an edge... It's just the creep that comes with struggling to maintain the necessary pressure.

It doesn't surprise me that Grip and Edge are equally sticky. I think, however, than Grip tends to be used in a thinner layer (3mm not 4 or 5mm) and on a sole with a softer midsole, which means it probably feels "stickier" on sloping holds, especially indoor volumes, simply because the softness of the shoe construction allows more contact area and more feel.

That's my off the cuff, shooting the shit theory, anyhow!

In reply to C Rettiw:

They're not equally stick tho'.  There is a difference... now 78 and 74 might sound similar, but the limits, 0 - 100 are so unusable to be irrelevant.. the usable part of the scale might only be 72 to 80.

In reply to Aled Williams:

My argument boils down to this, with all the variables like age related degradation, batch to batch variability, clean or dirty rubber, the effect of putting force through the rubber with its crystallisation and stress relaxation can you actually tell the diffrence between the two ? 

I dont think so especially with the XS series, it's most likely the structure of the shoe.

The unparallel rubbers seem to have a much larger scale one jas a Sh/A of 60ish the other 80Sh/A I think that would be much more noticeable 

In reply to Aled Williams:

It might just the be the difference between the 4mm and 3.5mm rubber, but....

One the crux foot hold of my long term project I cannot do it in anything other than the Instinct VS or Instinct Lace. I have tried in a freshly broken in in par if Instinct VSR (XS Grip) and the toe deforms and I slide off the hold. (it's a small, slightly sloping edge that relies on both toe rubber not deforming AND gripping well enough.. 

I'm just under 80kg and have noticed "toe roll" in many shoes over the years. 5.10 blancos were very prone to it once they were past their prime. New they were great, but they just softened with use and even when they had plenty rubber they became useless for anything hard.

Which your premise that "there may be as much overlap as there is difference" - on average XS grip will be softer than XS edge and therefor on average I would expect people to notice the difference.

Most of the time I don't, and hence why I do most sport and bouldering with Instinct VS. Recently ended up buying a pair of Vapour S slippers and I can really tell the construction and design led themselves much better to smearing and I've been quite surprised how much added confidence that has given me as a chronic edge clomper! Does the rubber help....?

In reply to Aled Williams:

 

this is totally beleavable. about 10 or more years ago salomon running shoes were panned by everyone. they were really skittish on wet rock, absolutely lethal, and they were all colourd rubber soles. salomon got the message and fixed it pdq

in a similar vain, not exactly the same but similar (I think). pro racing skis always have a black base - the clear or dyed plastics just arn't as fast.

In reply to Aled Williams:

Yes. 🤣

Fairly confident I’d be able to do a blind testing between grip and edge, particularly on a regular grit circuit 

In reply to Arms Cliff:

Well apparently the pros can't, so maybe you should get a free pair of shoes!

In reply to daWalt:

A lot of the Salomon running shoes that Ican think of with coloured soles are models like the speedcross. These are specifically designed for running on soft muddy surfaces and looking at the tread design it's obviously why they aren't great on rock. Also, a lot of Salomon, like many other brands, shoes still use coloured rubber.

In reply to Aled Williams:

Years ago, I forgot my climbing shoes on a boulder route setting day and borrowed a box fresh pair of Evolve Titan rental shoes from the centre to test the problems with (maybe around F4-F5c).

I distinctly remember my feet slipping around on big holds even though the shoes were well fitted. The rubber on those soles was awful in comparison to whatever Vibram compound was used on the Scarpas I usually bouldered in. There is certainly a difference in some rubber!