Your power VS tyre width ratio
Discussion
Captain Muppet said:
An interview with a ride and handling engineer I read a few years back said that they sized the driven tyres for traction (I assumed with some kind of target in mind) and the other tyres are sized for handling.
All the OEMs have huge teams of ride and handling engineers who will muck about with tyre sizes, compounds and pressures for months before selecting a production tyre.
Even the OEMs that produce bland dreadful cars put a lot of effort in to exactly how bland and dreadful the handling should be.
Thanks.All the OEMs have huge teams of ride and handling engineers who will muck about with tyre sizes, compounds and pressures for months before selecting a production tyre.
Even the OEMs that produce bland dreadful cars put a lot of effort in to exactly how bland and dreadful the handling should be.
It still doesn't explain why some cars have a such wide range of acceptable tyre widths. Take the X5, the same model and suspension can be had with 255/255 front rear or 275/315.
LeoSayer said:
Thanks.
It still doesn't explain why some cars have a such wide range of acceptable tyre widths. Take the X5, the same model and suspension can be had with 255/255 front rear or 275/315.
Because as has been explained in other threads about tyre profiles, the engineers will design an optimal whheel and tyre size and width. This will usually be the standard option. But then the marketing men will add some much bigger ones as an option for those who want a "sporty" look It still doesn't explain why some cars have a such wide range of acceptable tyre widths. Take the X5, the same model and suspension can be had with 255/255 front rear or 275/315.
papercup said:
Well, the RX7 has 520bhp and 530ft/lb and runs a 255 at the rear.
520bhp / 255 wide tyres = 2.04bhp per MM
530 lb/ft / 255 tyres = 2.08 lb/ft per MM
Its quite lively.
I'm presuming you have 2 back tyres though, so on the maths presented on the first post it would be 520/510 so 1.01.520bhp / 255 wide tyres = 2.04bhp per MM
530 lb/ft / 255 tyres = 2.08 lb/ft per MM
Its quite lively.
I had 500bhp on 255s before it grenaded
New motor I'm putting in now was dyno'd at 630bhp, so still on 255s that'll give 1.23 
Not to start another argument about winter tyres but
BHP: 280
Summer rears: 265/35, so 530/280 = 0.528 bhp/mm
Winter rears: 225/55, so 450/280 = 0.622 bhp/mm
The difference certainly feels greater than those figures would suggest; I’d guess that would be down to the sidewall height & compounds. I do prefer the narrower tyres though – you have to drive more – but they don’t give you the same margin for error.
BHP: 280
Summer rears: 265/35, so 530/280 = 0.528 bhp/mm
Winter rears: 225/55, so 450/280 = 0.622 bhp/mm
The difference certainly feels greater than those figures would suggest; I’d guess that would be down to the sidewall height & compounds. I do prefer the narrower tyres though – you have to drive more – but they don’t give you the same margin for error.
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