Narrower tyre to INCREASE wet grip?

[Samuel D]

There is an interesting claim in this article about the Michelin Pro4 Grip tyre, which was launched a couple of years ago but recently updated to a “V2” version:

“Rather counter intuitively this tread pattern is designed to actually reduce the amount of rubber that contacts the road in the wet. This increases the pounds per square inch exerted on the contact patch and helps the tire slice through the wet and stay glued to the raod.”

A similar claim is made here (though I’m not sure “hydroplaning” is the right term for riding on the very thin film of water between tyre and road).

Is this idea plausible?

If so, would not a 23 mm tyre at high pressure give better adhesion than a 35 mm tyre at low pressure, at least on a smooth enough road that suspension doesn’t become important?

This goes against most of what I know about grip (that reducing contact-patch area reduces grip, albeit by much less than the change in area).

[irc]

“Rather counter intuitively this tread pattern is designed to actually reduce the amount of rubber that contacts the road in the wet. This increases the pounds per square inch exerted on the contact patch and helps the tire slice through the wet and stay glued to the raod.”

I think it's just marketing speak. The tyre is virtually slick. I don't think that much tread will make any difference.

IMO the performance will depend on the rubber compound, tyre construction, and inflation pressure.

[reohn2]

Less rubber on the road at higher pressure mean less grip.

[ChrisButch]

I've no idea how its performance is related to width, but I can say (having used them in the winter for a couple of years now) that the Pro4Grip is a superb cold/wet weather tyre. It really does increase confidence in typical British wet/cold/muddy but not quite freezing conditions.

[pwa]

Downward pressure (once expressed as pound per square inch) is greater on a small footprint. That is why, when you pogo on soft grass (don't we all?) you sink in further than if you just jump up and down in your size tens. So yes, narrow tyres "bite" more than wide tyres if other factors are equal. I once stood beside a steep hill with snow on it and watched cars trying to get up. Cars with normal width tyres got up, but those with wide "performance" tyres could get no traction. Their tyres spread the load too wide. The advantage of wide tyres is that they "float" over soft ground, where narrow tyres put the weight on a smaller area and dig in.

[Brucey]

under most circumstances the road is much rougher than the tyre ever could be, and that roughness affects the contact area, the contact pressure and therefore the lateral grip. Even with a slick tyre the film of water is largely displaced wherever there is a high spot in the road surface that contacts the tyre. If you appear to have a large contact patch, actually only a small fraction of it may be in contact with the road, and that contact is locally at high pressure. The average pressure over the full apparent contact area (the deformed part of the tyre) is the same as the tyre pressure, but the local contact pressure is not.

Under these conditions changes to tyre width/pressure/rubber compound/tread pattern etc will make a difference to the local contact pressure and this may give a difference in the grip on offer.

However if the road surface is very smooth and/or it isn't just water on it, the local contact pressure can become the same as the tyre pressure and now you are more likely to skid. A tread pattern can have a greater effect here (in upping the local contact pressure), and so can a narrow tyre at higher pressure.

If it were as simple as 'bigger' 'smaller' 'softer compound' or 'tread pattern' when it is cold, wet, icy etc then all winter tyres would be the same; however... they are not. Maybe someone will do/has done a good tyre test on these; if there is anything there it ought to be possible to measure it.

cheers

[[XAP]Bob]

IIRC the physics of aquaplaning (or hydroplaning) are such that it isn't something that cyclists need to be concerned about.

[bobc]

Data from race car data logs from the greenpower national finals in 2013. These are electric race cars for schoolkids and our car "Dougal" was involved in 2 incidents in the pouring rain, first on lap 1 we spun off at 46mph at the "shell building" corner and in the 2nd incident we had to emergency stop from 43mph (took the same corner successfully at that speed) when a marshal with a black flag ran out onto the trackin front of the car (!!!). The skid was about 100 yards!
The first case was a sideways slide with no relative speed difference between road and tyre. The second longitudinal slide with 43mph difference in speeds.
In case 1 the calculated coefficient of friction was 0.406, in case 2 the calculated CoF was 0.402.
Schwalbe "durano" tyres (28mm I think) on 16" rims. Always inflated to 100psi at least.
The consistency of the 2 CoFs in different circumstances amazed me - clearly (that) bike tyre on soaking tarmac has a CoF of 0.4 - period!
Dry tarmac figures appear to be 0.9 to 1

[Tigerbiten]

As long as you leave rubber on the tarmac in a skid, then wider tyres give you more grip.

If you cannot leave rubber on the tarmac due to snow/mud,leaves,etc,etc, then narrower tyre can be better as they can cut down to the tarmac better.

[Samuel D]

I can say (having used them in the winter for a couple of years now) that the Pro4Grip is a superb cold/wet weather tyre. It really does increase confidence in typical British wet/cold/muddy but not quite freezing conditions.

Oh, I agree, having used the Pro4 Grip myself. I was just wondering why Michelin (a) gives it a tread, and (b) only makes it in 23 mm.

I have 25 mm Schwalbe One tyres at the moment, which I have found to be excellent in almost every way. But they just don’t grip as well as the Pro4 Grip in the wet, even though they’re slightly wider. I am making this judgement primarily on the ease of locking up the rear wheel while braking.

After suffering a fall this summer, I’m keener than usual to stay upright through the winter. The Pro4 Grip V2 appeals because I already have one used Pro4 Grip in decent condition, so could buy just one tyre to have a matched pair.

IIRC the physics of aquaplaning (or hydroplaning) are such that it isn't something that cyclists need to be concerned about.

Yes, but there is a film of water between tyre and road that reduces grip compared to dry days. I was wondering how that film is affected by contact pressure. Brucey makes some thoughtful points about this above.

Fluids can behave strangely in close proximity to objects (think of ball bearings in grease), so perhaps unintuitive things happen at the contact patch on a wet road. In fact, I’d love to learn more about this. Anyone know any books on the mechanisms of tyre grip?

Bobc: thanks for the coefficients of friction. If it’s feasible to calculate these experimentally, as you have done, why aren’t cycling magazines doing this? Knowing the true wet grip of available tyres would be invaluable info!

[reohn2]

I do not buy narrower/higher TP's increase wet road grip in real life use.
The bounce effect alone nullifies any such claim.

[mig]

my feeling is that the lower i sit and have my weight on a bike then the better it grips the road - especially through corners.

[Samuel D]

I do not buy narrower/higher TP's increase wet road grip in real life use.
The bounce effect alone nullifies any such claim.

Bounce certainly nullifies it on a sufficiently bumpy road. But what counts as sufficiently bumpy? On the sort of road I normally ride on, apparently the small suspension advantage of the 25 mm Schwalbe One over the 23 mm Michelin Pro4 Grip is offset by other factors affecting grip, since in the wet it’s easier to skid while braking with the former.

Still, subjectively I do feel safer with wider tyres. I think part of that is because, although most of the time the road is smooth, it is precisely when it ceases to be smooth that I’m most likely to lose traction on a corner – and then suspension really matters.

My bicycle can cope with nothing larger than 28 mm (even 28 mm is pushing it) so I don’t have a huge range of width choices open to me anyway.

I’ll be okay, but it’s an interesting topic.

[ChrisButch]

My bicycle can cope with nothing larger than 28 mm (even 28 mm is pushing it) so I don’t have a huge range of width choices open to me anyway.

.

I have the same constraint, which is why, in the threads about non-studded winter-specific tyres which usually crop up about this time of the year, I've often pointed out the frustrating gap in the market : there's nothing with a cold weather-specific tread compound between this narrow (23) tyre and the very much wider Conti Top Contact Winter. Every year I look for something in 25 or 28, but it's yet to appear. In the meantime the Pro4Grip does a very good job: although it does feel a trifle perverse to be riding x25 in summer and x23 in winter!

[[XAP]Bob]

I can say (having used them in the winter for a couple of years now) that the Pro4Grip is a superb cold/wet weather tyre. It really does increase confidence in typical British wet/cold/muddy but not quite freezing conditions.

Oh, I agree, having used the Pro4 Grip myself. I was just wondering why Michelin (a) gives it a tread, and (b) only makes it in 23 mm.

I have 25 mm Schwalbe One tyres at the moment, which I have found to be excellent in almost every way. But they just don’t grip as well as the Pro4 Grip in the wet, even though they’re slightly wider. I am making this judgement primarily on the ease of locking up the rear wheel while braking.

After suffering a fall this summer, I’m keener than usual to stay upright through the winter. The Pro4 Grip V2 appeals because I already have one used Pro4 Grip in decent condition, so could buy just one tyre to have a matched pair.

IIRC the physics of aquaplaning (or hydroplaning) are such that it isn't something that cyclists need to be concerned about.

Yes, but there is a film of water between tyre and road that reduces grip compared to dry days. I was wondering how that film is affected by contact pressure. Brucey makes some thoughtful points about this above.

Fluids can behave strangely in close proximity to objects (think of ball bearings in grease), so perhaps unintuitive things happen at the contact patch on a wet road. In fact, I’d love to learn more about this. Anyone know any books on the mechanisms of tyre grip?

Bobc: thanks for the coefficients of friction. If it’s feasible to calculate these experimentally, as you have done, why aren’t cycling magazines doing this? Knowing the true wet grip of available tyres would be invaluable info!

No doubt that wet grip is less, but you won't start aqua planing - that is a very different, and specific, problem.