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dose the size of rims effect the whp? i laid 109 with 205 50 17 if i would use my 15 for draging an dyno it again ho much of a diff will there be and what could i do to compensate for the loss if any between 15 an 17 rims

Do you have SRT struts on the car?


I don't know if it will affect actual horsepower numbers, but it takes less energy to spin a wheel/tire combo with a smaller moment of inertia. ie, takes less energy to spin a 205/50/15 than a 205/40/17.

like frank said, idk for sure (yet) if it affects numbers, but if my drag radials ever get here, I'll be switching from stock rims/tires after my first dyno run to 15" rotas and the dr's for runs 2&3. Still won't answer your question, but will show how much weight affects hp numbers.

If the circumference of the tire is kept the same so the speedo is the same between different wheels and tires, the only thing that should affect torque/horsepower would be the weight of the wheel/tire combination. Typically larger wheels weigh more unless you spend a bit more to get forged or semi-forged wheels. More weight means it'll take more power from the engine to get that extra mass moving. Lighter wheels dont' require as much force from the engine to get moving. Changing the size of the tires to make the tire circumference smaller or larger would most likely also affect horsepower and torque since in effect you're pretty much changing the gearing.

so going from 205/55/15 rim and tire being about 25lbs to 205/50/17 stock srt rims (i have no clue what the srt rims and tire wiegh) would that affect the hp?

yes because the 205/50/17 is taller and heavier. the car will be slower.

neon angel wrote:dose the size of rims effect the whp? i laid 109 with 205 50 17 if i would use my 15 for draging an dyno it again ho much of a diff will there be and what could i do to compensate for the loss if any between 15 an 17 rims

I may be wrong, but aren't the tire sizes/gearing factored in for the dyno run? I think the only way you would see the difference on a dyno would be to run one set, then swap the fronts and run again with the first parameters. That should give you the gain/loss. (If you want to get that scientific) As far as compensating, you either have to change the gearing, (not feasable) or add more power. But for street/strip use, the above posts are pretty much how it is.

Would you see gearing on the dyno? If I dynoed my car with my 3.55, then swapped in a 3.94, would the numbers vary?

Back to my post above, I believe the whp will change, just not the engine hp. I sorta misspoke in the previous post. The gear ratio/tire sizes put in will only keep the numbers consistent for engine power. If you were to run a smaller diameter tire, yes more torque/hp will reach the road, but it will not make the engine put out more power. The rpm range may be better suited for the application, tho. So yes the numbers should vary for WHP, at least the way I see it. I suppose it depends on what the dyno is programmed for, power to the ground or calculated engine output. I'm sure ppl with actual knowledge/experience could do better in answering this. I am merely speculating...

Please don't flame me if this is wrong, but it shouldn't matter at all because when you dyno a car all the gearing is taken into consideration and the car should be tested at it's direct gear, or closest to it so that you will get a more precise power curve.

By changing the gearing, all your doing is changing the "feel" of the car, meaning where it will spin more freely. It shouldn't change the end result at all.