My car came with the Cobb CT-One wheels that are 22 lbs. so I don't know how much it slowed the car down. The car is damn quick even with them. I'm getting lighter (16.5-17.5lbs) wheels mid-September, so I will be able to tell you how much quicker it is after that. Since it is rotating mass, it will probably cost you a few horsepower.

 

There is a rough formula for unsprung weight and it's effect on your performance. For each pound, multiply it by ten and then by four (four wheels) to see see the effect as weight added to your car. So, if you compared your wheel/car to the 12.5 lb. 17x7.5" SSR Competitions (~10lb. difference) on my car it would be 10lbs. X 10 X 4 = 400. That means, when we would race, our cars would come in equal if I had a two 200lb. friends in my car with me and you were alone in yours. It's a rough formula yes, but it gets you close.

 

also take into consideration the diametere of the rim
18's your slower than 16's

 

not necessarily, if you keep the same outer diameter then it all depends on weight, getting a lightweight wheel and tire in 18s can possibly make you go faster. then a heavier 16" wheel

 

To add to daredevil's thoughts, a 15lb. wheel can come in 16 or 18" diameters. The 18", though it accounts for the same amount of unsprung weight, will take more energy to start and stop spinning. This is because of the weight of the wheel being concentrated further from the center.

I have the 17" SSRs because they're rediculously lightweight, clear Brembo and other big calipers, look pretty nice, and they're rediculously lightweight. Not to mention the weight.

 

I don't think it's the wheels that are so light as much as it is the $375 per wheel removed from your wallet.
<--- Just jealous he can't afford them.

 

Easy guys - it's a big investment for all of us. There are less expensive wheels that are lightweight as well. Everyone's gotta find his/her ideal balance...

 

is that true? i've always wondered if its the actual wheel diameter or the overall diameter with tires that matters? say i had stock rims with 205/55/16 tires which had smaller wheel diameter but larger overall diameter, vs 215/40/17 with larger wheel diameter but smaller overall diameter, which setup would have a quicker acceleration?

 

Hmm...ignoring all else EXCEPT overall diameter the 215/40/17 will offer better acceleration.

 

hmm.. I'm not an expert in this field. but common sense is telling me that if your wheels are bigger then the engine doesn't have to spin them as fast as smaller wheels to maintain the same speed. so even tho the smaller wheels may accelerate faster thats only because they are smaller and need to spin faster.. not because your actually moving faster

make sense?

 

The diameter of the wheel has no bearing as to how fast it spins while driving, because the rim is not in direct contact with the road, the tire is. For instance, a 195/65/15 (25in Overall Diameter for a Continental Conti TouringContact CH95), 205/55/16 (24.9in OD)& 225/45/17 (24.9in OD)all have similar Overall Diameters, but different wheel diameters. So, if you remove the wheel diameter out of the equation & just pay attention to the tire's OD you will make it a question of ratios. If you go with a wheel & tire package with a smaller OD you are shortening your gearing, which will yield greater multiplication of torque & thus quicker acceleration. But, if you want a higher top speed (or better fuel economy) you will go with a package with a larger OD. That being said, you must understand that all this is highly academic and unless you are changing the OD by greater than .5in or more, because of all the possible variables involved.

The easiest way to wrap your brain around this is to think if riding a 10 Speed bike. If you wanted to pop a wheelie you would shorten the gears (chain on big sprocket in front & the smallest one in the rear) so you could get the front end up (acceleration). But if you were trying to race downhill, you would lengthen the gears (chain on the smallest sprocket in front & biggest in the rear) to reach top speed.

I hope this helps.