Big wheels = HP loss?

[RedBullitt]

i dont think it is really anything significant with wheels of that size. How much do they weigh?

 

[Hiltonizer]

larger wheels = rwhp loss?

rumourd that the rotational weight of larger wheels causes a loss of horsepower at the wheels

Can anyone verify/dismiss this?

I'd like to go with some nice 18x8's I found, and hope it wouldnt be too bad.

 

[NewStangNewbee]

i thought bigger wheels just meant faster times

 

[Green4.6GT]

the total outside diamiter of the tire is what will make a diffrence, if it is larger in total, tire and wheel, then it will have the reverse effect of getting gears, ie, if you have 4.10's and get a taller wheel/tire combo, then it will feel like you dont have 4.10's anymore.. because the ratio is now diffrent.

weight will also cost you alot in the wheel department, 10 lbs of rotating mass will cost you about a tenth in the 1/4.. so the lighter the better

-Ryan

 

[rjstaaf]

Typically when you go from a 17 to an 18 inch wheel it does increase your rotating mass even if the overall tire diameter is the same because most 18" rims are heavier than comparable 17" rims. You don't actually lose horsepower but, it takes more horsepower to turn the increased mass. You will also see the same affect when upgrading your brake rotors to a larger size, again typically more rotating mass.

 

[Aaron 4.6]

To put a finer point on the tech, going to a larger wheel doesn't necessarily add rotating mass. An 18 inch aluminum wheel can be lighter than a 15 inch steel wheel. However, the moment of inertia is proportional to the distance of the mass from the axis of rotation. An 18 inch rim has a significant portion of its mass 0.5" farther away from the axis of rotation (axle centerline) compared to a 17 inch rim.

Its kind of like spinning on an office chair with your arms and feet extended. As you pull your arms and legs in, you'll spin faster since the moment of inertia is less. Figure skaters do the same thing to accomplish those tight spins.

For a street car I would say this effect is not worth losing the 'bling' factor a nice set of wheels will give you.

 

[8yourZ06]

This may be a similar answer to the last post but putting bigger rims on will make a differance in your wheel horsepower. Even if the wheels are the same weight or lighter overall..the mass of the wheel is being put further away from the center of rotation. Therefore it takes more energy to get the bigger wheel rotating from a stop as well as more braking to get them stopped. The same can apply to adding bigger rotors for disc brakes. I did see on "Sports Car Revolution" (on Speed Channel) the result of adding bigger rims and larger brakes to their project Acura RSX Type-S. They made a baseline with the car totally stock and made another run on the dyno after adding exhaust and intake as well as bigger rims and rotors and the result was a loss in wheel horsepower. Granite it was a Honda, I think it was a good example.

 

[Joel's98GT]

heavy wheels = your car will be slightly slower.

perfect example, I saw a guy with a 98gt coupe 5-spd, bone stock, except O3 cobra rims. the thing was immaculate, well kept and very low miles. Looked fast. ran 15.1 all day long.

hell, i ran 14.55 the same day with H-pipe, shifter and stock 2.73 gear

 

[BLKsteeda]

I was recently told by Steeda when they dynoed my car that I would lose a little HP because of my wheels. I have Steeda Ultra Lite II 18x9.5 with 285/35 Nittos.

 

[ADRENLN]

i put 18 on my car, 10 in. wide in the back and 8.5 up front. the wheel weight was not the problem they were as light as stock, tires were the problem. 265 front 275 back. that added alot of rotational weight, that made the car feel sluggish. but they look so much better. i will just speed up the car now, no big deal.