Well, if I'm not mistaken, the Ion RL has 17" wheels. That's the maximum I'd personally go for a blend of looks and performace.

With the extra weight PLUS it being directed to the outside, will it hurt the Cobalt's acceleration? What if this makes it slower than the Ion RL?

 

You will lose some wheel HP due to the added weight to the wheels, and it might throw off the gear a little bit, but it might result in a higher top speed..

 

i was wondering how it will give it higher top speed, the over all diameter of the 17"and 18" are the same, its jsut that 17"s get higher profile tires.

 

The diameter might be close but the 18s are always going to be heavier unless you go with a super light rim which causes the hp loss

as far as going faster at higher top speed that might not change.. this im not sure

unless its cause of the rotations of the wheel

 

I don't see how it could increase top speed either as it requires more energy to move it (and to stop it).

It's not the weight itself. When you can have two items exactly the same diameter and weight and have them spin at entirely different rates depending on where the mass is distribute it. This is how figure skaters obtain a faster spin. They're not changing their mass, they're just pulling in their arms and legs towards the center of the spin. Less travel requires less energy. The energy would then be applied to the rotational speed.

We need some physicists here...

 

If a small wheel spins faster that doesn't make the car go faster, because it isn't going to travel as far with each spin. The height of the tire isn't going to make that much difference on top speed because gearing can make up for that. The width of the tire(narrow) and rolling resistance(high air pressure) will make the biggest difference.

 

^ ^ ^ you guys are both right. More mass farther away from the rotational axis will be more difficult to accelerate. On the other hand a smaller wheel will need to make more rotations to cover the same linear distance as a larger wheel.
This is part of the reason drag radials are small wheel with a large rubber tire( there are many others such as increased contact area).

I think in the case of a cobalt putting some lightweight 16's would help acceleration, as i believe the stock ones are rather heavy.

 

the profiles r the same, 45, the cobalt tire will be exactly 1" larger... 215/45x17, vs 215/45x18... if both cars have a 4.05 gear ratio, the effect of the smaller tire on the RL will make it seem to have a 4.22 ratio... or make the cobalt seem to have a 3.89 ratio...

 

It seems like you guys are getting it now. Assuming that a smaller rim and a bigger rim have the same overall diameter with the tire on, the one with the weight generally will rotate slower with the same amount of applied energy.

And assume you're going with a smaller overall diameter (which is not what the argument is about). Well, that's less weight plus your engine will just rev faster because it'll have to rotate more to cover the same distance at the same speed (putting out the same amount of energy to the wheels more or less).

With bigger rims, the weight is distributed to the outside. That mass needs more energy as it travels further than the mass on the inside.

I need to brush up on rotational mass/inertia and unsprung weight...

 

With a larger diameter overall, the rotations of the engine will be less for the same RPM as it takes less rotations to get the same tire speed, which would ideally lead to a higher top speed. The downside is that it lower acceleration as the tires will take more energy to spin at the same acceleration as they are larger.

 

Bah, you guys are worse than me sometimes.

Personal preference is all yours. Seems to me the trend lately is less space between the wheel and fender, and lower profile tires. A larger wheel accomplishes this more than a smaller wheel.

What if this makes it slower than the Ion RL?!? Then don't race it against an Ion RL, or a Neon or a V6 Malibu for that matter.

Otherwise, enjoy the car when you get it.

Villain

 

18's arent all that bad it all depend on the tire, have a crappy tire then yes 18's will hurt it. have a sticky tire then 18's will be good. the car was designed for use with 18's so thats how i'd keep it.

 

18's will get better handling than 17's (assuming same tires of course)

Handling pwns you all!!

 

A heavier wheel with a sticky sticky tire wil create less wheel spin when launching at the track, it might hurt your speed later on down the track, but that initial launch will be nice.