DYNO

[reality]

If you have a NA car on a dyno, will the numbers be different according to tire height? If so, why and how?
Tire weights assumed equal.

[Steve Wood]

...

[nocooler]

That's like asking if a bias-ply will dyno different than a radial. 

[reality]

Apparently the further the weight is from the center the more torque it uses to spin the tire.
Physics is not my strong suit.

[ULYCYC]

Tire/wheel weight would have more effect unless the tire size is a radical difference.  Air density from time of day would have more effect on results. 

[reality]

Thanks Guys ,
the number being thrown around is 20hp from 17 to 19 in rim.


Is this true?
A 4.0-1 rear gear with a 26 in tire.
Add 10% to the tire and  10% to the tire
4.4 gear 28,6 tire equals the same hp torque?
why or why not?

[ULYCYC]

I doubt 20hp unless a major weight difference between tire and rim. 

[daveismissing]

I would think you are right if you have a 10% larger tire but shift the diff gears by 10% this should be neutral?

[reality]

https://www.youtube.com/watch?v=OsmR3F6QMG8

[ULYCYC]

Dyno results are tested in  final drive  1to 1 in 3rd gear  or what ever your final 1 to 1 gear is.  Changing tire height, rim size or footprint  can all be lost accelerating from 1st gear to the final drive 1 to 1 street driving.   19" rims may look cool but suck trying to get out of the hole with a car that has any type of power.  That few HP gain that's still in a given margin of error doesn't mean squat in real word driving.   Taking the car to the track and change  tires, tune, fuel, carb/turbo and chassis will give you more useful data and results.