Testing Wet Weather Grip of Tires

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RyanH
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by RyanH

I recall a couple years back, a magazine threw on hockey gear and basically did a wet skid pad test until the tires gave out. Since then, I don't know if it's just a function of getting older and mortality creeping in, but I've become increasingly wary of descending near or around any wet pavement. With that being the case, I'd be interested in devising a test rig to simulate this somehow.

Can any engineers in the house provide some pointers on what such a rig should be? I envisioned something that would hold a wheel at a 30* or 45* angle with a fixed mass (e.g. 10 or 20kg) that would allow you to apply a pulling (or pushing) force until the wheel began to slide. Wet concrete and record maximal force prior to losing grip. Could also test on a steel plate as well to simulate manhole covers/other smooth surfaces like painted asphalt.

Thoughts?

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kode54
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by kode54

Too many variables on the road. My last crashed happened on a damp (not wet) surface. 3 riders went through ahead of me with no issues, while I must've hit the right spot on a reflector in the middle of the road or an oil spot and I went down. One rider in front of me had the same Schwalbe tires. These days, I'm extra careful with wet fall leaves (even dry surface but leaves are damp underneath).
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tjvirden
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by tjvirden

It would be absolutely fanatastic to have quantified measurements of tire grip on wet pavement; it's such an important aspect of tire choice, but currently users have no way of knowing what the precise differences are because no manufacturer publishes any information! I wish it was mandatory.

As for testing - I think Michelin's test rig is ideal, because it is a real-world test. If you haven't come across it, you can see it in action on YT in Michelin's publicity material for the Pro4. A single wheel test device is not at all easy to make when determining grip is the goal - either the wheel or the running surface has to be tilted, with accuracy and precision. In any case, a suitable device will be expensive.

Of course, determining the relative traction of tires on a defined surface is one thing; the inconsistency of pavement (traction) IRL means that the information from testing is still difficult to apply.

I have seen and experienced the situation described by kode54 - multiple riders get through the corner fine, one falls seemingly having done nothing different. Small variations in traction, from the huge number of variables that affect it, are the main causes.

TobinHatesYou
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by TobinHatesYou

kode54 wrote:
Sun Oct 17, 2021 9:14 pm
Too many variables on the road. My last crashed happened on a damp (not wet) surface. 3 riders went through ahead of me with no issues, while I must've hit the right spot on a reflector in the middle of the road or an oil spot and I went down. One rider in front of me had the same Schwalbe tires. These days, I'm extra careful with wet fall leaves (even dry surface but leaves are damp underneath).

For individual crashes sure. But you can still test the mechanical grip of various tires to help mitigate the risks.

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MrCurrieinahurry
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by MrCurrieinahurry

Maybe message peak torque (engineer bike guy off of you tube) see if he's interested in trying to create something?

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raffyyy
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by raffyyy

Is it safe to assume that cotton casing tires like Vittoria Corsa Controls will always have better grip than say a gp5k in all situations?

TwiggyForest
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by TwiggyForest

raffyyy wrote:
Mon Oct 18, 2021 12:32 pm
Is it safe to assume that cotton casing tires like Vittoria Corsa Controls will always have better grip than say a gp5k in all situations?
No, grip is largely determined by rubber compound.

kode54
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by kode54

TobinHatesYou wrote:
Mon Oct 18, 2021 6:01 am
kode54 wrote:
Sun Oct 17, 2021 9:14 pm
Too many variables on the road. My last crashed happened on a damp (not wet) surface. 3 riders went through ahead of me with no issues, while I must've hit the right spot on a reflector in the middle of the road or an oil spot and I went down. One rider in front of me had the same Schwalbe tires. These days, I'm extra careful with wet fall leaves (even dry surface but leaves are damp underneath).

For individual crashes sure. But you can still test the mechanical grip of various tires to help mitigate the risks.
Yes, agreed.
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jfranci3
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by jfranci3

So....
moist road has about the same grip as dry..... aside from oil/coolant spills/paint, which have zero grip.... this is pretty universal.

When you have water buildup, this is where car tire tread patterns matter. A bike tire is very narrow, so you don't worry about water evauation with the tread pattern. Car/motorcycle rain tires are all about the tread pattern and rubber compound, which is mostly about operating temp, which isn't that important for a bike tire. A soft compound helps ("racing tire"), but that also leads to cuts as the sharp object clings to the wet tire and gets a few chances to cut the tire. So.... don't worry about the tire so much as far as model of tire.

The thing about wet roads in all cases is that when you start to slip, you can't recover. Smaller tread blocks allow you to lose grip in a more controlled fashion (assuming there's grip) and recover smoother (so you don't get the aggressive recovery followed by a high side ejection). The key is not to exceed grip, so lower tire pressures and fat tires. lower pressures minimize the impact of smaller bumps, fatter tires give you a larger contact patch to work with.
https://www.velonews.com/gear/technical ... onditions/

I'd recommend learning about race car and motorcycle "Wet Lines" on race tracks. Bascially, you do more turning early in the corner, very little in the middle, then more at the end. The goal is not do any turning over the spots where cars leak oil/coolant.

Marin
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by Marin

I think Jarno at BRR is working on something IIC

tjvirden
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by tjvirden

So what's the difference between moist and wet?

I'm not at all convinced there's much similarity of technique, when cornering, for bicycles, motorcycles and cars. My experience is that they're each very, very different.

RyanH
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by RyanH

This is an interesting read on wet weather grip:

https://www.velonews.com/gear/technical ... onditions/

It seems, in summary, these factors influence wet weather grip:
  • Rubber compound (is the biggest factor according to Specialized)
  • Micro tread to fill into micro-crevices in the surface (e.g. a scuffed up tire is sufficient according to Specialized)
  • Tire pressure, lower increases contact patch
  • Suppleness of tire as it can more easily deform to irregularities in the surface to ensure maximal contact patch
So, real world wet weather grip will be hard to test but as mentioned above, I think there still may be merit to testing for coefficient of friction which should be a function of the first 3 bullet points.

Also, I disagree that moist asphalt should be similar in friction to dry. Anyone that has ridden up a steep street on a damp morning has experienced loss of traction in the rear when out of the saddle, with some tires being less prone to this (Conti comes to mind).

gruppetto
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by gruppetto

RyanH wrote:
Sun Oct 17, 2021 8:57 pm
I recall a couple years back, a magazine threw on hockey gear and basically did a wet skid pad test until the tires gave out.
Maybe it was the german Tour Magazin's test: https://www.tour-magazin.de/komponenten ... 10453.html

As far as I am aware they still include testing in wet conditions in their reviews.

jfranci3
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by jfranci3

There was a test in 8/2015, 6/2018, and 7/2019
All the 25c tires basically had the same grip with the lowest RR tires having the best grip... so the most compliant tire was slightly more grippy than the firmer ones. Moisture doesn't impact ashpalt/concrete grip, it does impact slip though.

tjvirden
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by tjvirden

I like the Tour testing in general, but I don't think it is as well quantified as they suggest. For me their wet weather tire testing is a case in point - I bought and used Schwalbe One's because the Tour testing put them very close to the GP4000S in wet traction. My real world experience was radically different! The Schwalbes weren't even close.

I think one issue is that it only takes a small change in the radius of curvature taken by their rider, to completely overwhelm other factors; in addition, it's not clear to me with what accuracy and precision they can measure the speed. Given that there's a V^2 (speed squared) term in the lateral (cornering) force, substantial errors appear easily there. Yet another significant complication is quantifying the camber of the test surface being ridden on.

So for my taste and experience the Michelin testing is far above any other. I have always found their tires excellent in the wet and I don't think it's a coincidence.

I also take the view, from my own experience, that it usually doesn't need much wetness (moisture) on the road to substanitally reduce traction, though the type of aggregates used changes this to a large extent. Some surfaces lose a lot of traction with only a little wetness, while others don't lose much even with a "fully wet" surface. This is what makes judging the available grip so difficult in the wet. If in doubt be cautious! I still come off now and then.

The Velonews article is, to me, a bit of a mixed bag. The manufacturer responses contain some good technical information, but also plenty of simple marketing/fluff with no backup at all. The Specialized and Conti responses are generally more helpful I think, though neither ideal. I think Lennard Zinn did well to get anything out of them.

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