Question? If I get my car dyno'ed with 17" wheels, then have the car dyno'ed with 18" wheels and the o.d. of the tire increases by a full 1", will the dyno Numbers increase or decrease going to a larger tire o.d. size?

 

it will decrease becuase of the larger rotating mass. assuming all other factors are equal between the 2 runs.

 

Let's say the mass is exactly the same, for debate purposes... More or less? With the larger wheel?

 

Will be the same, because the over all diameter of the wheel/tire itself doesn't change, cause 18" rims use thinner tires. But in reality, you'll loose power, that 1" more in the rim weighs more than you think.

 

The answer is, and this is base I my original question, The Horsepower will stay the same, but the torque will decrease.

Remember I said the tires Outside Diameter is larger for the 18" versus 17" and the mass is exactly the same.

 

http://www.audizine.com/forum/showthread.php?p=4416002

also read up on sprung vs. unsprung weight

 

18s vs 17s you have the same overall diameter (including tire) so the speedo wont be off. Every 1lb of extra rotating mass is about the same as 10lbs of dead weight.

 

Are you people illiterate? He said in the first post...

Therefore he means that if he dyno's with a 275/45/17, he's probably going to dyno with a 275/45/18 tire so the aspect ratio won't change and the overall diameter will increase by the 1".

 

Thankyou! Mr. Xemeth.

regards,
jEFF