wouldnt a lighter rim the same size as stock add horsepower (by releasing power normally lossed to the drivetrain)? I heard somewhere that if you reduce the weight of anything that spins on the engine or drivetrain that you will free up horsepower. If this is true it seems like a lighter wheel the same size as stock would free up power and reduce weight for better acceleration. Anybodys opinion would be appreciated.

I dont think it actually adds hp, I could be wrong. But what I do know is that it is less rotating mass. Which makes it feel like you hvae more hp. I remember reading something a while ago that gave a conversion on if you drop so many lbs in rims and tires it gives you the this much more hp feeling.

My 14" stock wheels are very noticeably faster than my 16" stockers. The smaller wheels, even with tires mounted are quite a bit lighter than the 16's. As for HP, dunno, never dynoed my wheels. ;)

Dan Green
99'RS

Your question was actually in a car magazine. I forget which one, but it wasn't one of the mainstream ones.

It was either import racer! or Hot Compacts and Imports (HCI).

The article showed that lighter wheels of the same diameter actually DO increase horsepower.. in their dyno runs (yes, more then one dyno run for each wheel setup), they actually achieved a 3-5 horsepower gain from wheels that were each six pounds lighter then the original baseline wheels.

also, total diameter of the wheel alters your gear ratios. For example, Larger then stock wheels = higher top speed (if we didn't have a limiter on our ecu).

That was just off the top of my head from the article.. if you have anymore questions, post it or email me.

Lighter wheels increase the wheel hp reading on a chassis dyno, but of course they don't effect the crankshaft hp.

Basically, if you have a heavy wheel, you have to expend more energy (horsepower) to turn it versus a lighter one.

Now, going into alot more detail (I didn't minor in Physics for the fun of it!), more weight means you get a higher rotational inertia of the wheel and tire. Higher rotational inertia means it has more resistance to turning (inertia, the tendency of an object to stay at rest) and it takes more power to turn the wheels.

This is especially if the extra weight is due to heavier tires. The tread of the tire is on the outside of the diameter of rotation. The more weight you have pushed out to the outer diameter of rotation, the higher the rotational inertia.

An example of this is if you roll a sphere, a disk, and a hoop down a hill, (regardless of weight) the sphere will ALWAYS reach the bottom first, followed by the disk, and the last to reach the bottom is always the hoop. The hoop has all of it's mass at the outer edge of it's rotation, thus giving it the highest rotational inertia.

Thus, if you have the same rim, and run two tires of the EXACT same weight, but one tire is a 195 and the other is a 245, the car will be slower with the 245 compared to the 195 since the mass of the wider tire is concentrated in the tread, which is at the outer edge of rotation of the wheel/tire combo.

This could vey well mean tire weight and tread width could play a more important role than wheel weight, but wheel weight is still important.

I have seen this from experience. I was 2-3 tenths faster with the stock 195/70 tires on stock alloy rims at the drag strip versus my aftermarket setup (see below), even though the rx-7 rim with the tire only weighed 36 lbs, 13.8 lbs for the rim, 22.2 lbs for the tire. The stock bridgestone 195/70 tire weighs 20 lbs. The stock rim, not sure, but it's pretty light.

>also, total diameter of the wheel alters your gear ratios.
>For example, Larger then stock wheels = higher top speed (if
>we didn't have a limiter on our ecu).


We DON'T have a speed limiter. Just a rev limiter ;-)

If you do decide to run lighter wheels your car will be faster. You are not making any extra horsepower at the block but you are losing less horsepower at the wheels. In essence you are simply making more efficent use of the horse power that you have. That is why when we go to the strip we run 24.5 by 13 inch wheels and we run them with about 5 psi. They are very light and they have a wide tread width. The low tire preassure lets the tire buckle and this gives you a great launch.

I read or heard somewhere that removing 1 pound from the wheels is like taking 20 lbs from the body. So if you can take 2 pounds off each wheel, it would be like taking 160 pounds from the car itself. Umm...

Cool. I just got new 16" Enkie wun guns. I dont like the way they look much (too small), but the car seems to be faster. I was just making sure my theory about freeing up lost power was correct. Thanks guys

the OZ car are limited supposively. i think it's just the automatics cause i think vegasdsmer has an OZ and he's always talin about hitting 120 130 blah blah blah. soo