Query / Advice re: new tyre on Vauxhall Astra

Rodney_Trotter

AdrianC wrote: »

Overly simple, I think.

The tyres on the "good grip" side will have the same amount of grip.
The tyres on the "poor grip" side will have much less.

If the theory that ABS only pulses the "poor grip" tyres is correct, then the tyres on the "good grip" side will still have exactly the same maximum braking effort. Sure, they'll be slowing a greater proportion of the car's weight, but that won't have a massive effect on the braking distance, although it will give them much more heat to dissipate.

So are you saying one wheel on mud is the same as 4?

If not then JC is correct.

Jamie_Carter

AdrianC wrote: »

Overly simple, I think.

The tyres on the "good grip" side will have the same amount of grip.
The tyres on the "poor grip" side will have much less.

If the theory that ABS only pulses the "poor grip" tyres is correct, then the tyres on the "good grip" side will still have exactly the same maximum braking effort. Sure, they'll be slowing a greater proportion of the car's weight, but that won't have a massive effect on the braking distance, although it will give them much more heat to dissipate.

On modern ABS systems, the ABS will only cut in on the wheels that lose traction. This is to keep control of the vehicle, rather than decrease stopping distance.


To provide the shortest stopping distance the brakes would need to provide steady braking to all 4 wheels, at a pressure that just allows each wheel to keep turning. And not by pulsing the brakes. But ABS systems aren't capable of doing this.


To simplify this: If all 4 wheels would lose grip at lets say 100kg each on an even surface, then the total stopping force would be 400kg. If the wheels on the left had side of the car were on mud, and would only provide 10kg each stopping force before they lost grip, but those on the right hand side provided 100kg each, then in this situation the total stopping force would be 220kg. This would vary slightly due to the constant locking and releasing of the wheels on the left, but it gives you a general idea.

Jamie_Carter

AdrianC wrote: »

I had Conti PremiumContacts on the Saab 900 T16 - very decent grip, far better than the Mich EnergySavers that preceded them, and not far different from the Mich Pilot Primacies before those. But they wore much, much more quickly.

The biggest problem running older performance cars these days is getting good enough tyres in the right sizes.

The better grip, but higher wear rate would be due to a softer compound.

AdrianC

Jamie_Carter wrote: »

On modern ABS systems, the ABS will only cut in on the wheels that lose traction. This is to keep control of the vehicle, rather than decrease stopping distance.

Have you ever driven a car with, say, one front brake not working?

Jamie_Carter

AdrianC wrote: »

Have you ever driven a car with, say, one front brake not working?

I'm not sure what you are getting at??


Do you mean not working because the callipers have seized, or the ABS not working??

AdrianC

Jamie_Carter wrote: »

I'm not sure what you are getting at??

Do you mean not working because the callipers have seized, or the ABS not working??

The former. An imbalance side-to-side. Life gets very... unstraight.

Jamie_Carter

AdrianC wrote: »

The former. An imbalance side-to-side. Life gets very... unstraight.

To be fair, no I haven't as I make sure my vehicle is maintained properly. However if a brake wasn't working on one wheel, then ABS wouldn't work on that wheel either.