Wheel sizes on rolling roads

[Lucky Dave]

The question is does running different sized wheels make a differance to RR figures.

Im thinking differing overall sizes.

Im running 215/35/18 at present but have in the past ran 205/45/15 which is way smaller!

The question is do the smaller wheels give more torque?

The run down losses measure friction of a moving mass which I think may not be 100% spot on as the other is torque?

I hope someone can explain or even try my theory on the dyno!

[GTT 280]

different wheel sizes will have a bearing on the bhp figure, as will your tyre pressures. All this has been debated (at great length and pain) in the forums. Just search for Rolling Road BHP WHP.

Cheers,
K.

[Ant FR]

cool i best get mine re rollered

[GTT 280]

Quote: Originally Posted by Ant FR (original)

cool i best get mine re rollered

...be sure to wear the full sparco race suit and helmet if you do... just in case.

Cheers,
K.

[Silent1]

Providing the dyno is set to the gearing of the car there shouldn't be any difference

[MarkW]

it is one of the many many inaccuracies in rolling roads.

[MINI-Morgan]

Smaller overall size of tyre/wheel combo must give more torque as less torque is required to accelerate with a smaller wheel. But does the dyno account for this on the run down?? surely yes as a smaller wheel will require more torque to turn that a bigger one. Think about bigger and smaller pulleys but also factor in drag from friction

[Lucky Dave]

Im thinking its a bit like doing a dyno run in 3.5 gear.

And runs in 3rd have given more power in the past if it will grip.

[Bhozar]

Would be good to try out a few different size wheel combo's and a hub dyno, to see if there are any differences.

[Silent1]

Quote: Originally Posted by Bhozar (original)

Would be good to try out a few different size wheel combo's and a hub dyno, to see if there are any differences.

To use a hub (proper) dyno the wheels are taken off!

Do you mean a chassis dyno, i.e. one you drive on?

[Bhozar]

Quote: Originally Posted by Silent1 (original)

To use a hub (proper) dyno the wheels are taken off!

Do you mean a chassis dyno, i.e. one you drive on?

Nope. I mean put the car on a chasis dyno with several different sets of wheels, then put it on a hub dyno without the wheels.

[Paul]

Then take the engine out and put it on an engine dyno, so you know the drivetrain losses too.

[Ant FR]

then take the engine out on the back of a trailer driving at 80 mph whilst dynoing on a mobile dyno to see what really happens in real world.

Failing that bung the oprator a tenner and get him to mess around with the settings and increase your BHP

[Lucky Dave]

Quote: Originally Posted by Ant FR (original)

then take the engine out on the back of a trailer driving at 80 mph whilst dynoing on a mobile dyno to see what really happens in real world.

Im liking this idea!