Tyres for the wet

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meic
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Re: Tyres for the wet

Postby meic » 28 Nov 2009, 4:27pm

I agree that when you need the grip most you may well be on the sides of your tyre, leaning the bike over, however that isnt really the case that we are discussing here.

This is about the other occasions like staying in control when you hit a puddle
or braking which is best done in a straight line
or in my last case trying to cycle up a dirty hill also generally done in a straight line.

In fact compared to on the motorcycle, I dont seem to lean the cycle often at all.
The lack of suspension probably makes the tread irrelevent.
Yma o Hyd

thekelticfringe
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Re: Tyres for the wet

Postby thekelticfringe » 28 Nov 2009, 4:30pm

drossall wrote:No, I don't see how tread can lock with road surfaces. It's the deforming rubber that would do that, so the rubber compound and inflation pressure will matter more than the tread.


Well perhaps *both* things are going on at the same time? One effect doesn't rule out the other one. For sure the rubber deforms on a microscopic scale, but maybe could also engage with the road surface at a cm or mm scale?
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thekelticfringe
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Re: Tyres for the wet

Postby thekelticfringe » 28 Nov 2009, 4:57pm

meic wrote:In fact compared to on the motorcycle, I dont seem to lean the cycle often at all.


Meic - slightly OT, but when I rode a motorbike I was told to move my bodyweight to the inside of the corner which has the effect of keeping the bike a little more upright. Ridng a mountainbike I've been told to lean the bike over as far as possible and keep an upright body position and weight on the outside pedal. So I'm interested if you have different techniques for cornering when cycling c/w on the motorbike?
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meic
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Re: Tyres for the wet

Postby meic » 28 Nov 2009, 5:10pm

Not really that I have noticed.

Almost all of my time on the bike is at slow speeds and on the motorbike was at higher speeds.
At somewhere below 20mph the whole way that you steer changes.
It is not often that my bike goes fast enough to practice countersteer.

Then there is the need to pedal which changes things.

Also the different techniques that you mention could be road v offroad and my offroad experience is limited to a few seconds after some road experiences. :D

On the other hand I could be doing a lot that I dont notice.
Yma o Hyd

bensonboo
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Re: Tyres for the wet

Postby bensonboo » 28 Nov 2009, 5:59pm

meic wrote:
Also the different techniques that you mention could be road v offroad.


Just watch how a motocross rider corners, it confirms what you say, the bike will be as flat as possible but the rider upright, usually ready to dab his foot as the tyres wash out.

niggle
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Re: Tyres for the wet

Postby niggle » 28 Nov 2009, 10:29pm

meic wrote:At somewhere below 20mph the whole way that you steer changes.
It is not often that my bike goes fast enough to practice countersteer.


I am convinced countersteering is essential when turning virtually any two wheeler at anything above walking pace, trouble is it is a tiny twitch of the very light steering on a bicycle which we do not realise we are doing, but all that wobbling when we were first learning to ride a bike was about learning to countersteer, IMO.

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meic
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Re: Tyres for the wet

Postby meic » 28 Nov 2009, 10:34pm

On reflection you are right about that.

The reason I know is

The first time that I tried to ride a motorcycle and sidecar, I could not do it.
Even at walking speed or slower I just could not turn the handlebars in the direction that I wanted to go. Years of motorcycle riding had taught my subconcious that you just dont do that sort of thing.
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EdinburghFixed
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Re: Tyres for the wet

Postby EdinburghFixed » 28 Nov 2009, 11:18pm

thekelticfringe wrote:
drossall wrote:No, I don't see how tread can lock with road surfaces. It's the deforming rubber that would do that, so the rubber compound and inflation pressure will matter more than the tread.


Well perhaps *both* things are going on at the same time? One effect doesn't rule out the other one. For sure the rubber deforms on a microscopic scale, but maybe could also engage with the road surface at a cm or mm scale?


Tread does engage with the surface, but it does so by sinking in - this is what makes chunky mountain bike tyres so effective. However tarmac road surface is harder than tyre rubber, so the effect of tread is actually to lift away contact area by recessing it.

If you look at mountain bike tyres, you can see a clear progression between tread and surface:

Image

1. huge tread, mud.

Image

2. regular tread, mixed surface

Image

3. Minimal tread, hardpack

Image

4. No tread, sealed surface

- once the tread cannot sink in, it is a question of getting the maximum possible surface area in contact (all other things, like rubber softness being equal). Hence a completely slick tyre offers the maximum possible grip on road.

drossall
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Re: Tyres for the wet

Postby drossall » 29 Nov 2009, 12:43am

meic wrote:The first time that I tried to ride a motorcycle and sidecar, I could not do it.
Even at walking speed or slower I just could not turn the handlebars in the direction that I wanted to go. Years of motorcycle riding had taught my subconcious that you just dont do that sort of thing.


You get the same effect riding an upright trike.

thekelticfringe
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Re: Tyres for the wet

Postby thekelticfringe » 29 Nov 2009, 9:17am

Playing on a mate's quad gave me problems of a similar nature, plus every time I stopped it I suibconsciously tried to put my feet down.
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thekelticfringe
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Re: Tyres for the wet

Postby thekelticfringe » 29 Nov 2009, 9:33am

EdinburghFixed wrote:once the tread cannot sink in, it is a question of getting the maximum possible surface area in contact (all other things, like rubber softness being equal). Hence a completely slick tyre offers the maximum possible grip on road.


I'm not sure. I understand the progression, and MTB tyres 'digging in' is a clear and demonstrable effect (- many walkers have pointed it out to me in a sorta negative way :? ). But there's a few bits of your suggestion I don't think I've quite understood.

1) "Lifting away contact area". The total contact area is determined primarily by the weight of the rider and tyre pressures. So a treaded tyre running at the same pressure and with the same load on it will have a total contact area the same as a slick - it will just be more spread out. (I'd agree that there are some minor factors I've discounted - a very stiff sidewall will resist deformation and slightly reduce contact area at low pressures etc.)

2) A slick provides lowest *rolling resistance* because there are no knobs or tyre irregularities to deform as the tyre rotates. I think that the absence of tread is primarily to maximise speed/reduce rolling resistance.

3) I was wondering what happens if you take your suggestions to the logical extreme. Perhaps this would mean that a slick would perform best on a very smooth surface, where the contact is absolutely maximised - say a polished concrete/terrazo style of surface? Anecdotally I've found such surfaces (wet or dry) to be considerably less grippy than the road, which maybe suggests there's at least one other factor in play here?.
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thekelticfringe
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Re: Tyres for the wet

Postby thekelticfringe » 29 Nov 2009, 9:36am

meic wrote:my offroad experience is limited to a few seconds after some road experiences. :D


LOL - hope it all ended well :lol:
Pedal faster, I hear banjos!