I know this topic has been covered before but I have to bring it back up again because of the number of people that I see and read about, who tune their cars to race, but still use 17 and 18 inch wheels.
From what I understand, the smaller the wheel, the better acceleration you will get, because of the smaller number of revolutions your tire makes, and the lighter weight combined with more weight closer to the point of rotation. In other words, if you have 2 cars ( same torque/horsepower etc.), one with 15 inch wheels, and one with 18 inch wheels, and you give them both 10 seconds to a move at a constant rate, the one with the larger wheels will have moved a shorter distance, because it takes slightly longer to make 1 revolution, than the smaller wheel.
Well if this is the case, than why are so many people racing with 17, 18, even 19 inch wheels ? Does this mean that the difference in acceleration between the wheel sizes is negligable ? Also, if my above stated 2 car scenario is true, why do the serious drag racers have little 15 inch wheels in back, and tires that look like they must be about 20 -22 inchs in diameter in the front ? Doesn't that go directly against the smaller wheel/faster acceleration theory ?

 

The slicks you see the "serious racers" using up front are that tall because the sidewalls are designed to flex. The treads are very sticky so the sidewall flex gives the treads time to hook up and then sort of slingshot the car away once the treads are hooked.

 

From what I've heard, people use the largest rim necessary solely for the purpose of clearing brakes. Even when you go to a larger rim of the same weight, the increased rolling diameter still requires more torque to spin compared to a smaller rim.

I'm no expert in this, so i'll let someone explain the details

 

For our hondas, outside of cosmetics, there is no reason to go to larger 17-18" wheels. There aren't very many big brake kits for our cars to begin with, and the few that do require a larger wheel to fit are mostly overkill.

A lightweight 15x7.5" wheel is generally considered "optimal"; you'll see drag racers and autocrossers use 13" wheels on occasion (but finding tires in those sizes is a bit tough).

Now I know a lot of road racing hondas use 17-18" wheels, but on a road course, taller gearing is more important. Either way, as long as the wheel is light and strong ($$$), the worst that can happen (say you get an 18" wheel) is that you won't suffer too much of a decrease in performance.

I recently chose to "upgrade" to a 14 lb. 17x7.5" wheel for cosmetic purposes mainly.

Shingo

 

on this topic... i am building a show car, what is the widest 18" rim i can tuck under my wheel wells? and what offset...

 

i think up until 18" it doesnt really matter. i mean if you have a 15" wheel and tire, and a 17" wheel and tire, and both wheel tire wheighs the exact sameit wouldn't make an difference, because the rim is taller, but the tire is shorter, making them still the same size together.
sorry for all the commas and if this doesnt make sense.

 

Dudes.

He's talking about big gumball slicks like these:



Not 17" wheels or whatever.

 

i didnt see anything about slicks in the original post....:dunno:

 

Not quite so.

A larger wheel has a wider distribution of rotating mass, requiring more torque to turn overall, even if the wheel weights the same as its smaller counterpart. The issue about keeping the wheel/tire diameter the same is tricky, since a 195/55/15 tire is actually slightly taller than a 215/40/17 (common size) tire if I'm not mistaken.

I think MrFatBooty answered the latter part of the original poster's question; I'm just commenting on the wheel sizes he listed...

Shingo

 

ok, thanks for your feedback guys