Author Topic: Wide Slick Tyres - inherently poor wet grip?  (Read 1111 times)

Wide Slick Tyres - inherently poor wet grip?
« on: April 16, 2018, 11:01:44 pm »
I know this might sound obvious but with the current trend in wider tyres I wondered if anyone else has experienced a proportional and somewhat alarming lack of grip in the wet with wide >35mm slick tyres?  I'm guessing that at relatively high pressure the contact patch is smaller than a narrower tyre so there's less grip and at low pressure there's a big enough contact patch to aquaplane?
Most of the stuff I say is true because I saw it in a dream and I don't have the presence of mind to make up lies when I'm asleep.   Bryan Andreas

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #1 on: April 16, 2018, 11:10:04 pm »
Read this: http://www.sheldonbrown.com/tyres.html#tread

Down at 40psi you'd need to do 104kph to aquaplane.
"Yes please" said Squirrel "biscuits are our favourite things."

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #2 on: April 16, 2018, 11:44:11 pm »
Read this: http://www.sheldonbrown.com/tyres.html#tread

Down at 40psi you'd need to do 104kph to aquaplane.
Though I do subscribe to his theory with respect to "traditional" road tyres, Sheldon's calculations appear to be derived from a 1963 report from Flight International and seems to ignore the difference in weight between a bicycle and the maximum landing weight of a DC3 and also the fact that aircraft tyres have a water dispersion tread. 
Most of the stuff I say is true because I saw it in a dream and I don't have the presence of mind to make up lies when I'm asleep.   Bryan Andreas

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #3 on: April 17, 2018, 07:19:30 am »
It's more to do with the compound than anything else, in my view.

Whatever other factors may be involved, mostly surface lubrication, it REALLY isn't aquaplaning. To aquaplane, you need to be going fast enough for the water to form a barrier and for the tyre to lift off the ground.

For many years I used Conti SportContact slicks for commuting in a round-about 35mm / 1.6" configuration and found them to have reliably better wet grip than any tread tyre I tried. Downside was puncture resistance (lack of) and wear.

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #4 on: April 17, 2018, 08:21:45 am »
Yes ^^^ Modern quality compounds and tyre designs are better, and better at  managing the conflicting requirements of good grip, good wear, good puncture resistance  - but it's always a trade-off. And our expectations have risen. Can anyone really remember what tyres were like years ago?

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #5 on: April 17, 2018, 08:45:00 am »
Aquaplaning is a red herring, a dead stinky fish, but there are other ways to lose grip. Compound important and I reckon tread does play a role in the wet, despite the theory being that it doesn't.
The earth is vast and beautiful and contains many miraculous places. (Chekhov)

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #6 on: April 17, 2018, 10:30:05 am »
Fluids behave oddly (i.e. unlike fluids) in thin films, which may be why the mechanism by which tread patterns allegedly improve grip on wet hard ground is not clear to me. In other words, someone still needs to convince me of that! It’s not intuitive to me.

I believe Brucey of this forum attributes grip improvements with tread patterns to increases in local contact pressure. Given the softness of rubber and the suppleness of the casing, I don’t see how this effect can be large, especially since in general the opposite is true with rubbers: greater contact area increases friction (slightly).

At any rate, the effect of tread patterns is dwarfed by differences in tread compound. Many fat tyres, probably including the Vittoria Voyager Hyper given its overall performance, use low-hysteresis compounds to reduce rolling resistance. Wet traction relies on hysteresis so this is directly detrimental to grip.

Although tyre science has improved greatly in the last three decades, I’m less convinced that the wet grip of bicycle tyres has generally improved. On the contrary, I think it may have diminished as carbon black was replaced by alternatives such as silica in an effort to improve other aspects of a tyre’s performance, notably the rolling resistance. Puncture protection has improved enormously, albeit at a cost. Wear and ageing have improved. But wet grip? Probably only in a handful of special-purpose tyres like the Michelin Pro4 Grip (that I mention often because its wet grip is so impressive).

mattc

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Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #7 on: April 17, 2018, 10:31:18 am »
Aquaplaning is a red herring, a dead stinky fish, but there are other ways to lose grip. Compound important and I reckon tread does play a role in the wet, despite the theory being that it doesn't.
Yes - tread is reducing the amount of rubber on the road. So it reduces your grip (very slightly in practice).
Has never ridden RAAM
---------
No.11  Because of the great host of those who dislike the least appearance of "swank " when they travel the roads and lanes. - From Kuklos' 39 Articles

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #8 on: April 17, 2018, 10:37:31 am »
Well that's the theory! I'm not sure really. I do think that compound is more important. I'd also say that although roads are often wet they are virtually never just wet – there's always oil, dust (quite a lot of it from tyres!), mud and stuff mixed in with that water. Getting back to the OP's point, I don't think wide slick tyres are any more likely to lose grip than narrow slick tyres of the same type.
The earth is vast and beautiful and contains many miraculous places. (Chekhov)

LittleWheelsandBig

  • Whimsy Rider
Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #9 on: April 17, 2018, 10:55:42 am »
I suspect (on the basis of little hard knowledge) that tread patterns give some feedback of approaching the point of losing traction while slicks tend to be 'all or nothing'.
Wheel meet again, don't know where, don't know when...

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #10 on: April 17, 2018, 10:55:50 am »
if the road surface is smooth and/or there is a film of something other than water present then you can indeed start sliding around like nobody's business.

In essence, for good grip in the wet you need the road and/or the tyre to be rough in some way.

Jobst Brandt's tests are often cited as evidence that 'slick tyres have plenty of grip in the wet' but an oft-missed feature of those tests is that he was riding on nice clean grippy tarmac (equivalent to if not actually) shell delugrip, which had rainwater on it, but nothing else.  My experience is that if you ride round the UK on low pressure slick tyres as if the conditions are like that, it will not be long before you end up on your ear, because they are not....

The conditions for a full aquaplane are 'no contact at all' between the tyre and the road, at which point you have no ability whatsoever to brake or steer. Needless to say you can lose a substantial amount of grip well before this, and this can be unsettling or dangerous; on a bike you don't need to have a full aquaplane to have reduced grip and a skid, so the arguments concerning aquaplaning are indeed somewhat specious.

IME with wide-ish slick tyres at low pressures there are plenty of situations that risk a nasty skid and worse yet, the transition from 'some grip' to 'not enough grip' can be very sudden.  Treaded tyres can have lower levels of grip under some conditions (eg in the dry) but generally break away in a fashion that allows more  warning.

Things to look out for when riding low pressure slick tyres

- worn out tarmac
- overbanding
- manhole covers
- spilt diesel
- 'road film' (containing oil etc in summer or road salt in winter)
- mud
- green slime
- wet leaves

etc etc

None of these things is always very visible when the road is wet and in fairness you are likely to be in trouble on treaded tyres too. But IME the trouble will be less bad and the onset of trouble will be clearer to you.

If you have narrow tyres at high(er) pressures they will push through any given film of crud more easily too, so there are certain conditions where you will get more grip that way, too. 

In the case of slick tyres the contact pressure (on a slick surface) simply defaults to the tyre pressure. In the case of treaded tyres the contact pressure can be higher than the tyre pressure so again the tyre can push through a layer of slime or w.h.y. more easily.

FWIW I will happily ride in the summer on wide low pressure slicks, just taking extra care when conditions are poor.  In the winter I prefer a treaded tyre if it is wide or a narrow tyre with higher pressure in it (which can have less tread but some is still better than none). Even a simple file tread on the tyre shoulders (as was long-favoured for racing) gives more feedback when cornering in the wet and of course doesn't slow you in the slightest in a straight line.

cheers

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #11 on: April 17, 2018, 11:19:03 am »
you will note that in the above post I didn't mention rubber compound.  It is not that it won't make any difference (it will) but that it has an almost separate effect from the other matters under discussion.

Given a certain tyre width/pressure, absence of tread, and given road conditions you will of course get more or less grip with compound type.

  But that is usually reliant on there being some kind of roughness on the road surface, so that more of the tyre can push through the crud film and have a chance of gripping.  In a roughly  similar way the high spots on any tread pattern can push through such a film too.

Thus there is always a mixture of microscopic (local) contact pressures being altered/limited by tread design and rubber compound vs average contact pressures in the contact patch.  Arguably if the crud film has perfectly linear viscosity properties it shouldn't make that much difference, but this is (for various reasons) rather unlikely, so it does.

Whilst you can measure lateral G (and therefore grip) to this day the final arbiter of (esp car and motorcycle) tyre performance is often 'a tyre tester', i.e. a human being. Needless to say these chaps are experts and can perhaps feel a tyre start to break away a bit earlier than most folk. An averagely (in) competent rider/driver may not feel the same things as clearly, so a tyre that suits an expert may not suit an average rider at all.

 There is also the matter of conditions. Tyre tests are carried out on test tracks and these are largely devoid of the hazards that are present on normal roads.  Thus a tyre that scores OK for wet grip on test might still be a bit of a handful on real roads.

cheers

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #12 on: April 17, 2018, 12:00:07 pm »
I suspect (on the basis of little hard knowledge) that tread patterns give some feedback of approaching the point of losing traction while slicks tend to be 'all or nothing'.

Not the case with the Contis, which I felt were reassuringly progressive and able to regain grip well. I think the biggest definable difference is between high pressure/low contact area, where I would expect a more sudden loss of pressure as compared to low pressure/large contact area.

Kim

  • 2nd in the world
Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #13 on: April 17, 2018, 12:32:33 pm »
Aquaplaning is a red herring, a dead stinky fish, but there are other ways to lose grip. Compound important and I reckon tread does play a role in the wet, despite the theory being that it doesn't.
Yes - tread is reducing the amount of rubber on the road. So it reduces your grip (very slightly in practice).

Hang on, isn't the amount of rubber on the road governed by the tyre pressure?  For the same weight and pressure more siping should just mean a larger 'contact' patch (the actual area in contact should stay the same).  Which presumably affects the grip, and is why knobblies get squirrely on corners.
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #14 on: April 17, 2018, 01:59:47 pm »
I came off early February on mud with 50mm Big Apples while taking a 'short cut'.
Had my fifth round of physio yesterday and my neck still hurts. Won't be doing that again!
Never knowingly under caffeinated

mattc

  • "Hannibal"
  • n.b. have grown beard since photo taken
    • Didcot Audaxes
Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #15 on: April 17, 2018, 04:27:51 pm »
Aquaplaning is a red herring, a dead stinky fish, but there are other ways to lose grip. Compound important and I reckon tread does play a role in the wet, despite the theory being that it doesn't.
Yes - tread is reducing the amount of rubber on the road. So it reduces your grip (very slightly in practice).

Hang on, isn't the amount of rubber on the road governed by the tyre pressure?  For the same weight and pressure more siping should just mean a larger 'contact' patch (the actual area in contact should stay the same).  Which presumably affects the grip, and is why knobblies get squirrely on corners.
I think it's one of those things where you have to qualify everything with:
"all other things being equal ..." and of course they rarely are!
Has never ridden RAAM
---------
No.11  Because of the great host of those who dislike the least appearance of "swank " when they travel the roads and lanes. - From Kuklos' 39 Articles

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #16 on: April 17, 2018, 04:45:31 pm »
if you have a tyre at a given pressure the overall size and shape of the contact patch is governed by the tyre pressure, and is about the same whether the tyre has a tread or not.

However if the tyre is treaded, the contact pressure is increased. This can reduce the grip in the dry, but can increase the grip when there is slimy crud on the road.

cheers

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #17 on: April 17, 2018, 07:05:55 pm »
I came off early February on mud with 50mm Big Apples while taking a 'short cut'.
Had my fifth round of physio yesterday and my neck still hurts. Won't be doing that again!

I have a set of stabilizers going spare I can send you nobby .I care about your safely  ;D
I hope that your neck pain disappears soon  :)
the slower you go the more you see

vorsprung

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Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #18 on: April 17, 2018, 09:17:50 pm »
gurt big slick tyres on muddy surfaces are worse gripping than expected

I don't feel that wide slick tyres are somehow a lot worse than narrow slick tyres or tyres with more tred in the wet

but going from a dryish road to a muddy path it is noticably different
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Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #19 on: April 17, 2018, 10:15:50 pm »
I have a set of stabilizers going spare I can send you nobby .I care about your safely  ;D
You are such a caring chap  :)
I hope that your neck pain disappears soon  :)
It will soon. I'm about to close this tab!  ;D
Never knowingly under caffeinated

Re: Wide Slick Tyres - inherently poor wet grip?
« Reply #20 on: April 18, 2018, 09:44:52 pm »
Whilst you can measure lateral G (and therefore grip) to this day the final arbiter of (esp car and motorcycle) tyre performance is often 'a tyre tester', i.e. a human being. Needless to say these chaps are experts and can perhaps feel a tyre start to break away a bit earlier than most folk. An averagely (in) competent rider/driver may not feel the same things as clearly, so a tyre that suits an expert may not suit an average rider at all.
cheers
and it was my experiences as a human being riding wide slick tyres that prompted my OP.  However, I am by no means an expert and had previously enjoyed countless thousands of "off" free sedate cycling miles on traditional tyres before my foray into wide slicks in pursuit of comfort for last year's LEL.  Brucey also wrote "FWIW I will happily ride in the summer on wide low pressure slicks, just taking extra care when conditions are poor.  In the winter I prefer a treaded tyre if it is wide or a narrow tyre with higher pressure in it (which can have less tread but some is still better than none)."  Wise wise words :thumbsup:
Most of the stuff I say is true because I saw it in a dream and I don't have the presence of mind to make up lies when I'm asleep.   Bryan Andreas