Rolling Road Tyre Pressure?
Turbo Mini Forums

Interested to know, what tyre pressure do you use when you know you have a rolling road session?

Tim

89' Metro Turbo
157 BHP , 170 lb ft @ 15psi .... So far....
Mikeanics Rolling Road
WINNER OF RETRO CARS SHOW BEST 80's MODIFIED CAR

Hi,
A little higher (3-4 psi) as you've got two load areas on the tyre instead of one. But the more important part is to use the same pressure everytime!
Cheers,
Gavin :)

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I just use 30psi in mine.

I'd ask the RR operator what he recommends. its easy enough to do when you get there.

50% more only if your tyres are up to the job

depends on the condition of the rollers aswell, some rollers struggle for grip

I've seen the future and tbh its Pie

Well if the RR Calculates the losses and not guesses them like many then I shouldn't make ANY difference weather your pressures are at 2 psi or 32 psi! As the OVER all fig will be right!!

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
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It will make a difference

a big difference!

Higher pressures = less rolling losses

Any rolling road will measure them too..... not sure what you mean buy "guess" matt.

Alex

AlexF

He means that, when the RR gives you wheel HP you should pump them up as hard as possible to get the highest number (and fit the narrowest tyres). A good rolling road, with coast down will calibrate this out. Sadly there are more bad than good.

Try explaining to one of the wheel HP brigade that their plot is a case of emperors new clothes and they often get a bit upset.

Even on a brand new - fresh installed and calibrated - your tyre pressures effect the contact patch.

Even with the best software calculating your run down losses you will not be able to cancle out increased tyre presssures.

Ask Dave Walker - or Ford.

Alex

AlexF

well it has been shown on the rollers that we use that if your tyre pressures are low, of you oil is cold and thick or a different grade, you get a different BHP @ Wheels, than with hot oil and hard tyres.

HOWEVER WHEN you add the losers which will be more to the lower BHP @ wheel figure the OVER ALL FIG IS ALWAYS THE SAME. not sure I can be any more clearer But all rollers measure power differently, so on same yes it will make a difference.

Edited by Miniwilliams on 8th Mar, 2007.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

calculated run down loss plus wheel power should equal crank power.
The losses are inevitable, but when there is a twin roller system the tyre trys to ride up the front roller and trys to creep under the rear roller. It is the latter that you need to reduce to a degree, as this causes the tyre to pinch between the rollers increasing drag. However, this can also be used as a benifit to increase the grip.

Put it this way, if you are looking for a fairly representative figure that is what your car is putting onto the road then you need to increase the tyre pressure some what to compensate the increase in drag on the rollers thats not there off the rollers. The other thing to consider is that the coast down is not the same as when under power. The tyres are not being pinched into the rollers so the drag is different and the results will always be inacurate. Then theres the drag of the rollers to contend with, that gets thrown int te equasion as well.

I got the '50%' information from a bloke who works in the emissions test department chassis dynamometer of a very large well known petrochemical company. It must be some sort of specification they use to standardise the test results.

There will always be a debate on this, and as far as im concerned you should go with what you feel is right based on what you consider to be the right way. Each to their own

Acuracy is what you want it to be