Tyre wet grip and efficiency ratings.

[Doctordiesel77]

Now that the drought is over and the motorways seem to be full of people that either haven't noticed, or don't know that water alters their stopping distances I thought I'd do a few tyre & stopping distance related sums. Having witnessed a incredible displays of stupidity on the M6 a couple of years ago I bought a set of tyres that were A rated for both wet grip and efficiency. I knew that A would be better than B, C, D, E or F, but not how much better. Having found the specs for the wet grip ratings I have worked out the approximate stopping distances from 70mph in feet, excluding thinking time for a new tyre: A is 106, B is 111, C is 126, E is 137, F is 150, I didn't bother with G, as I had worked out that I did the right thing when I got to C. Then I did it again for a tyre with 2mm of tread left, still legal, but time for a change really...increase in distance is generally agreed upon as 44-50%, I assumed 44%, this gives distances of: A 153, B 160, C181, E 197, F 216. Interesting that a crappy tyre on its last legs more than doubles the stopping distance over a new A rated one, also interesting that an A rated one on its last legs is not much worse than a new F rated one. The worrying thing about this is that these differences are much bigger than the maximum claimed reduction in stopping distance given by modern anti skid braking systems (0-30%, depending on several variables and which of the many theories you believe). This implies that my old car could outbrake a modern car if the modern car had F rated part worn tyres on... Add the fact that the average tailgater is undoubtedly a bit thick, probably hasn't done any sort of pre-journey checks & may or may not react rapidly..... I'm beginning to wish I hadn't done these sums.... The rolling resistance sums I couldn't be bothered to do, working out the effect of an xKg per tonne drag on the fuel consumption of a car that contained 81 horses when it came out of the factory, but some of the 81 might be having a nap now doesn't sound like a ten minute sum fest, this web site implies that it it won't have done any harm though... https://dynamon.co.uk/resources/burn...ng-resistance/

[Jeff Turbo]

Been tailgated many times and often wondered how they would stop if I had to brake hard, nearly rammed a few times in the past. I always leave a gap in any of my cars, just in case. I've seem plenty of tail end smashes to know how it ends up sometimes.
I also had a new car pull out in front of me while driving my Consul, that has drums brakes all round and I had to swerve as well as slamming my brakes on as the stopping distance is a lot further, plenty of verbal that day aimed at the ****

[Doctordiesel77]

I guess you tend to notice the mentally subnormal drivers more, but there seem to be more of them about than there used to be, very annoying when they get closer to your car instead of clustering around the other halfwits as they battle to get to the next services 2 seconds sooner.

[Jeff Turbo]

I did an experment a few years ago. Drove the way i normally to down to a job in essex, on the way back i drove inside all speed limits. The difference was less than 5 minutes for 170 miles.

[Morris Montego]

I guess you tend to notice the mentally subnormal drivers more, but there seem to be more of them about than there used to be, very annoying when they get closer to your car instead of clustering around the other halfwits as they battle to get to the next services 2 seconds sooner.

"but there seem to be more of them about than there used to be" - I guess this is because so many are now driving huge SUV type things and are ultimately less aware, feeling more in a cocoon , invincible.

[Morris Montego]

.....and SUV, Sports Utility Vehicle - I've always thought this a contradiction in terms. How can a UTILITY vehicle have a sporting focus??!

[Morris Montego]

.......I mean my Countryman has a load of practicality, a dose of style, plenty of performance, drives well, nicely.......but a sports car, no

[Morris Montego]

"Interesting that a crappy tyre on its last legs more than doubles the stopping distance over a new A rated one" " these differences are much bigger than the maximum claimed reduction in stopping distance given by modern anti skid braking systems (0-30%"

Now, that does surprise me, didn't think tyre condition would affect stopping distance quite so much. And also, I thought the benefi

[Morris Montego]

.......and also I thought the benefit of anti lock brakes would out weigh that of having top notch tyres,


You learn something every day

[Doctordiesel77]

.......and also I thought the benefit of anti lock brakes would out weigh that of having top notch tyres,


You learn something every day

I wasn't sure about it, so thought I'd do the sums when I came across the figures associated with the wet grip ratings. The thing that is often forgotten/ignored about abs is that it was introduced to enable you to steer during heavy braking, rather than to reduce stopping distance. Maximum braking force is just before the tyre skids, so when abs pulses it goes from under max, to max, to quite a bit under when the abs releases the brake,then back to max & repeats, the average braking force is less than it would be if there was a way of applying the ideal braking force. There are a few pages online where people claim that they can outbrake abs..I went with the 30% improvement & gave abs the benefit of the doubt!

[Morris Montego]

"The thing that is often forgotten/ignored about abs is that it was introduced to enable you to steer during heavy braking" - yes, I remember the Granada advert, tractor on country lane