Tyre "reaction time" in the wet?
Discussion
MartinM said:
Can anyone give me a rough idea of how much longer a tyres take to react to steering input in the wet as opposed to the widely accepted 0.25secs in the dry?
Cheers
Martin
Cheers
Martin
Why should it take any longer in the wet? I don't know where the 0.25 figure comes from or how widely accepted that is, but I'd expect most of the delay to come from the time taken to build up lateral deflection in the sidewall and suspension bushes. This deflection would be proportion to load applied, if anything it should be less in the wet since the loads will be lower. The time taken for the body to yaw and roll will usually be much longer than this anyway, surely that is more important?
Does it really matter anyhow?
I must say I'm very sceptical about these references to a 0.25 second delay. Are we sure it's not 0.2 or 0.3 seconds?
Surely it varies according to quite a range of factors, so can we really settle on a figure and make any use of it? I suspect not.
Given that Reg advises us to apply steering input gently at first and then a bit more rapidly - rather like the varying intensity of braking - it hardly seems important to me. In any case I don't think we want to be jerking a car into the bends. Ease it in smoothly and gently, and you're less likely to come unstuck, I would say.
Best wishes all,
Dave.
I must say I'm very sceptical about these references to a 0.25 second delay. Are we sure it's not 0.2 or 0.3 seconds?
Surely it varies according to quite a range of factors, so can we really settle on a figure and make any use of it? I suspect not.
Given that Reg advises us to apply steering input gently at first and then a bit more rapidly - rather like the varying intensity of braking - it hardly seems important to me. In any case I don't think we want to be jerking a car into the bends. Ease it in smoothly and gently, and you're less likely to come unstuck, I would say.
Best wishes all,
Dave.
MartinM said:
Ok, i probably didnt word it right. What i was getting at was how much longer percentage wise would people estimate it takes the steering tyres to achieve maximum grip in the wet.
The quarter second reference comes from Don Palmer.
The quarter second reference comes from Don Palmer.
I still don't get why you're asking, but my answer is that it makes no difference at all since the delay you're talking about is a property of the tyre and suspension bushes not of the level of grip available.
You are dealing with a few separate effects here:
1. Tyre relaxation length - this is the distance rolled by a tyre between the generation of a slip angle (i.e. you applying the steering) and the tyre generating the full force related to that slip angle. This is about one circumference of the tyre, so makes a lot more difference at 2 mph compared with 30 mph.
2. Transient handling - the time taken from the initial application of steering to the car settling down to a steady state of cornering. This is a function of the suspension design (both spring and damper rates and the geometry) and as the Hairy Don says, it's around a quarter of a second, but it varies between cars.
If you notice, neither of these things relies on the coefficient of friction between the tyre and the road and are effectively unchanged in the wet.
1. Tyre relaxation length - this is the distance rolled by a tyre between the generation of a slip angle (i.e. you applying the steering) and the tyre generating the full force related to that slip angle. This is about one circumference of the tyre, so makes a lot more difference at 2 mph compared with 30 mph.
2. Transient handling - the time taken from the initial application of steering to the car settling down to a steady state of cornering. This is a function of the suspension design (both spring and damper rates and the geometry) and as the Hairy Don says, it's around a quarter of a second, but it varies between cars.
If you notice, neither of these things relies on the coefficient of friction between the tyre and the road and are effectively unchanged in the wet.
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