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?

It is possible that it may throw your speedo off a little bit here check this link it will show u stock vs aftermarket sizes http://www.miata.net/garage/tirecalc.html Dude!

it also depends on how tall the tire is.. if you are running a tall tire on a 17" wheel.. and going to a real low profile wheel on a 18" wheel.. it shouldn't matter at all..

It's not the overall tire diameter or circumference I'm talking about. It's rotational mass. Like when figure skaters pull their limbs in to obtain a faster spin. Their mass doesn't change. The parts that were pulled towards the center have less travel and the energy that would have been used to move their apendages is now going into the speed of the spin.

For example, it takes less effort to rotate a 10lb solid disk which is 10" wide. You've got another 10lb solid disk that is 15" wide. Putting towards the same amount of energy, the 10lb, 10" wide disk will spin faster than the 10lb, 15" disk.

Anyway, in this example, I'm excluding the tire from the equation. You can imagine a 0 lb tire which makes the overall diameter 20" for the above.

It's where the majority of the mass is distributed. If it's distributed to the outside, then it will require more energy to make it rotate as fast as something that's got the mass biased to the inside.

If the 17 and 18 have different series tires and their diameters are the same, the only factor would be weight.

Then again, will they have a different series tire.

If the 17 and 18 have different series tires and their diameters are the same, the only factor would be weight.

Then again, will they have a different series tire.


What a tool!

It's not the overall tire diameter or circumference I'm talking about. It's rotational mass. Like when figure skaters pull their limbs in to obtain a faster spin. Their mass doesn't change. The parts that were pulled towards the center have less travel and the energy that would have been used to move their apendages is now going into the speed of the spin.

For example, it takes less effort to rotate a 10lb solid disk which is 10" wide. You've got another 10lb solid disk that is 15" wide. Putting towards the same amount of energy, the 10lb, 10" wide disk will spin faster than the 10lb, 15" disk.

Anyway, in this example, I'm excluding the tire from the equation. You can imagine a 0 lb tire which makes the overall diameter 20" for the above.

It's where the majority of the mass is distributed. If it's distributed to the outside, then it will require more energy to make it rotate as fast as something that's got the mass biased to the inside.

Perfect explaination sir! Yes, it will make the car accel slower, I'm sure that's not what anyone wants to hear, and 1/2 will argue this point, but it's right on the money. Without adjusting the final drive gear, which is 4.05 in both the Ion and the Cobalt, the larger rim will accel a little slower. If they manage to play with the rims enough, they can eliminate alot of the difference, but not all of it. When I dropped 17" rims on my Camaro, from the stock 15", there was NO question that it was slower. REALLY pissed me off, after that I learned the lesson of rim size/weight vs. ease of rotation. It's also the same concept that makes a front engine/AWD car turn slower and harder than a mid-engine RWD car. The weight is spread all over the AWD car, where as with the other car, the weight is localized nearer to the middle of the car.

i believe it's the same on the RL is 215/45/17 and the SS is 215/45/18

i say yes...

when they're out, im sure ppl will run them with the stockers, then put some 17's on them, and see if they gained a tenth or two.. hey.. it could happen..

i believe it's the same on the RL is 215/45/17 and the SS is 215/45/18

That doesn't mean they're the same diameter, it's just as wide and has as an equally sized sidewall. See here (1010Tires.com) (http://www.1010tires.com/tiretech.asp#sizing) and here (tire calculator) (http://www.1010tires.com/tiretech.asp#sizing). So it looks like both the tires and wheels will be heavier on the Cobalt SS.

Anyway, there's a lot more to the rotational mass/unsprung weight issue I'm not qualified to answer. I'm no physicist/engineer (although my work title claims I am an engineer. hehe). It's very possible that a 20lb 16" wheel will spin much more easily (and faster) than a 17lb 21" wheel.

You've got to make a compromise/sacrifice somewhere. Looks vs performance. But I see a problem. I think downsizing the wheel size of the Cobalt SS while keeping OEM diameter will make the tires look crazy fat. It may also hurt handling because your sidewall will allow for more flex. Not using OEM tire circumference will throw off your speedometer/odometer readings.

If you want your speedometer/odometer to remain correct, one possible solution I can see is using the ION RL's OEM tire size and (if interchangability allows) swap out the Cobalt's vehicle speed sensor for the one in the ION RL. The difference may be as simple as a gear used to adjust for the tire size. But sometimes these things are in your differential and you may need to crack open the tranny for this. Keep in mind this is all speculation. This should not be attempted until someone confirms this is possible.

From all the reviews I've seen (not always the best source but anyway), they believe the Cobalt SS is slower than the Ion RL by ~0.2 sec.

i believe it's the same on the RL is 215/45/17 and the SS is 215/45/18

Yea, that actually says that the tires will be larger. Means the car has the same thickness of sidewall on a larger rim.

I hear the Cobalt SS's wheels weigh in at 25lbs each! That a heavy wheel! I would definitely go with some lightweight, aftermarket wheels like OZ SLs to get yer rotational mass down.

I hear the Cobalt SS's wheels weigh in at 25lbs each! That a heavy wheel! I would definitely go with some lightweight, aftermarket wheels like OZ SLs to get yer rotational mass down.

i agree.. lighter and smaller will bring the times down a tenth or two for sure!

I hear the Cobalt SS's wheels weigh in at 25lbs each! That a heavy wheel! I would definitely go with some lightweight, aftermarket wheels like OZ SLs to get yer rotational mass down.

It's not real easy to find aftermarket rims with the right bolt pattern at this point. Plus, a 25lb wheel, I believe that's with the tires, for an 18" rim, isn't that bad at all. There were some people out looking for 18's for their Redlines, and one guy was smart enough to look for wheel weight, and the first set of wheels he looked at were almost 40lbs a wheel. I don't know how credible that is, but that's what he said. I'm pretty sure someone weighed the Redline wheels w/tire and said that it came in at just under 22lbs. How light do some of these rims get to?

Edited: I just found this website...
http://www.wheelweights.net/
There are alot of 17" wheels that weigh more than 25lbs!

I hear the Cobalt SS's wheels weigh in at 25lbs each! That a heavy wheel! I would definitely go with some lightweight, aftermarket wheels like OZ SLs to get yer rotational mass down.

Mmmmm... OZ Superleggeras... As yummy as Christina Aguilera.

My wheels are 17" and 20lbs. I consider them heavy. My 16" wheels weigh 16lbs. That's not including tire.

Yea, that actually says that the tires will be larger. Means the car has the same thickness of sidewall on a larger rim.

Not neccessarily. It is the aspect ratio of sidewall to width. It can and does change on wheels of different width.

There may be a lot of wheels are that are over 25lbs but there are several that are much much less... like under 18lbs. I beleive the Centerlines and most to all Rota wheels fall under this weight.

Not neccessarily. It is the aspect ratio of sidewall to width. It can and does change on wheels of different width.

I'm fully aware of that, look at the numbers again. If you have two tires with identical stats like that- 215/45/18, 215/45/17, what this says is, both tires will have a side wall that is 45% of 215mm. The same height. If both tires are, say, 1" sidewall heights, then the wheel/tire diameter will be 18" for the 17" rim/tire combo, and 19" for the 18" wheel/tire combo. If you want the wheels to be the same size you will need something around a 35 series tire on the 18" rim.

I just plan on gettin lighter 18"s. I just couldn't make myself go to a smaller rim, even if it would help performance.

I am looking for rims For my Cavalier at the same time as the Cobalt. I am down to 2 rims depending on how much I am going to blow on the Rims. LOL

for My Cavalier I am looking to buy Motegi TrackLite forgeline in a Flat Black 17x8 at 14.5lbs each $325 a wheel

For the Cobalt I am looking at the same Motegi Tacklite 19x8 which will be 18lbs and about $400 a wheel.
http://www.motegiracing.com/wheels/details.asp?parent=50&wheelid=51&name=TRAK_LITE Flat Black&style=2388&desc=

I am also looking at a set of Forgeline wheels the S03P which are about $1,000 a wheel. I am going to find out weight info soon.
http://www.forgeline.com/wheels/so3p.html

well guys look at it like this... it may actually benefit the car... For instance SS Camaros had 17" wheels as opposed to the Z28s 16"... Yet they hook a hell of a lot better... So bigger wheels may not be a bad thing, is it just me or does the tire width on the CObalt not look small?

well guys look at it like this... it may actually benefit the car... For instance SS Camaros had 17" wheels as opposed to the Z28s 16"... Yet they hook a hell of a lot better... So bigger wheels may not be a bad thing, is it just me or does the tire width on the CObalt not look small?

215s... didn't the SS have steeper rear gearing as well though?

nope the only difference between the SS and the Z28 was the Cold-air, exhaust, and spring rates... Also I've known people to throw SS wheels(and Ws6 wheels on Trans Ams) on a Z28 and pick up a little bit in trap speed... Its no "huge" difference but it does show that the extra inch does not hamper performance in any way...

There is some company called AutoVelocity or somethin like that and they are making custom carbon fibre wheels. They say that their wheel featured in the PHR mag was an 18"*10" or 10 1/2" and it only weighed 8.5lbs!!!!! :eek:
And they say that they are at LEAST TWICE as strong as a stock Z06 wheel. They claim they will custom make each wheel for any vehicle....
for the LOW LOW price of $1500 PER WHEEL!!!

I'll be getting some :D ...when I win the lottery :(

There is some company called AutoVelocity or somethin like that and they are making custom carbon fibre wheels. They say that their wheel featured in the PHR mag was an 18"*10" or 10 1/2" and it only weighed 8.5lbs!!!!! :eek:
And they say that they are at LEAST TWICE as strong as a stock Z06 wheel. They claim they will custom make each wheel for any vehicle....
for the LOW LOW price of $1500 PER WHEEL!!!

I'll be getting some :D ...when I win the lottery :(


wow, 9lbs... :eek: , thats pretty crazy, but the price is gay :mad:

Yeah thats what I thought. They actually look pretty good.
But who can afford that????
I'm gonna try to see if I can scan the article and post it up...
Not that it will do any good cause the only people who can afford to have them made are people who own Ferraris and the like and ummm... they just probably aren't on this particular site much. LOL

That doesn't mean they're the same diameter, it's just as wide and has as an equally sized sidewall. See here (1010Tires.com) (http://www.1010tires.com/tiretech.asp#sizing) and here (tire calculator) (http://www.1010tires.com/tiretech.asp#sizing). So it looks like both the tires and wheels will be heavier on the Cobalt SS.

Anyway, there's a lot more to the rotational mass/unsprung weight issue I'm not qualified to answer. I'm no physicist/engineer (although my work title claims I am an engineer. hehe). It's very possible that a 20lb 16" wheel will spin much more easily (and faster) than a 17lb 21" wheel.

You've got to make a compromise/sacrifice somewhere. Looks vs performance. But I see a problem. I think downsizing the wheel size of the Cobalt SS while keeping OEM diameter will make the tires look crazy fat. It may also hurt handling because your sidewall will allow for more flex. Not using OEM tire circumference will throw off your speedometer/odometer readings.

If you want your speedometer/odometer to remain correct, one possible solution I can see is using the ION RL's OEM tire size and (if interchangability allows) swap out the Cobalt's vehicle speed sensor (http://www.racepages.com/parts/vehicle_speed_sensor.html) for the one in the ION RL. The difference may be as simple as a gear used to adjust for the tire size. But sometimes these things are in your differential and you may need to crack open the tranny for this. Keep in mind this is all speculation. This should not be attempted until someone confirms this is possible.

From all the reviews I've seen (not always the best source but anyway), they believe the Cobalt SS is slower than the Ion RL by ~0.2 sec.

From what I understand both the speedometer and the odometer are determined by the pulse signal sent by the speed sensor at one of the wheels. The vehicle computer basically is just using the number of rotations of the wheel, the factory wheel circumference and gear ratios to determine the speed and mileage of the car.