unsure about my new wheels

[bedlam13]

so i have a wheel question for you guys. i've searched, but i didnt find what i was looking for on the CTS.

i recently purchased a set of 20x8.5'' wheels for my '04 CTS, and they have a +35mm offset. i purchased them from a company that guarantees the fitment of the wheels, but most of the wheels i see for the CTS have around a +40mm or higher offset. does anyone have a +35 offset on their CTS, or know if they will in fact fit?

when i mounted the wheels (without tires) to check the bolt pattern ect., they did seem to clear everything but it was close on the inside rear. any help would be greatly appreciated. thanks. LOVE the site btw. lots of good info!

[Cadillac Jim]

I don't have offset information on the CTS. Here's some interesting points about front suspension concepts.

A double wishbone front suspension will have a lot of variables in the design. The most important of these is the steering axis; this was once called the kingpin axis, and is the axis about which the front wheels rotate when the steering wheel is turned. In a double wishbone front suspension, this is a function of many things, such as the amount of spring compression and how far the steering wheel has been turned. In a strut suspension, it is simply the axis of the strut, and this fact does not change with spring compression or steering angle.

To avoid or minimize steering wheel torques with uneven road surface or front wheel traction -- or torque steer in FWD under similar conditions -- the steering axis must pass through the center of the tire patch. This simple fact has led to the use of strut front suspensions in most modern cars, from economy entry-level cars to Formula 1 and Indy racers.

Your car has a strut front suspension. To maintain drivability, i.e. avoid starting steering wheel torques, you need to keep the steering axis passing through the center of the tire patch. This is most simply done by keeping the original suspension geometry: the tire rotating diameter and the wheel offset. If you change one, you should change the other in proportion to the steering axis offset from vertical. Changing the rolling diameter effectively changes the final drive ratio, and I don't recommend it. I have seen VSS speedometer calibration change kits for sale but I can foresee the possibility that if you try to use one it will bring up persistent OBD II codes that require that you take if off for several days before you get state emissions inspection to let the codes clear. Thus you should try to stay within 2% or so of your OEM tire rolling radius.

As I said, I don't know what the offset is on the CTS, but on my 1997 Eldorado I believe it is 42 mm; I would have to spend some time in the FSM to make sure. I have seen replacement wheels with 40 mm that say that they match my offset, and perhaps 2 mm in a tire patch 7 inches (178 mm) wide, perhaps it is good enough -- but I would want a 42 mm offset on the wheels I put on my car, so long as the tires have a 26.6 inch rolling diameter, plus or minus 2% or so.

[bedlam13]

I don't have offset information on the CTS. Here's some interesting points about front suspension concepts.

A double wishbone front suspension will have a lot of variables in the design. The most important of these is the steering axis; this was once called the kingpin axis, and is the axis about which the front wheels rotate when the steering wheel is turned. In a double wishbone front suspension, this is a function of many things, such as the amount of spring compression and how far the steering wheel has been turned. In a strut suspension, it is simply the axis of the strut, and this fact does not change with spring compression or steering angle.

To avoid or minimize steering wheel torques with uneven road surface or front wheel traction -- or torque steer in FWD under similar conditions -- the steering axis must pass through the center of the tire patch. This simple fact has led to the use of strut front suspensions in most modern cars, from economy entry-level cars to Formula 1 and Indy racers.

Your car has a strut front suspension. To maintain drivability, i.e. avoid starting steering wheel torques, you need to keep the steering axis passing through the center of the tire patch. This is most simply done by keeping the original suspension geometry: the tire rotating diameter and the wheel offset. If you change one, you should change the other in proportion to the steering axis offset from vertical. Changing the rolling diameter effectively changes the final drive ratio, and I don't recommend it. I have seen VSS speedometer calibration change kits for sale but I can foresee the possibility that if you try to use one it will bring up persistent OBD II codes that require that you take if off for several days before you get state emissions inspection to let the codes clear. Thus you should try to stay within 2% or so of your OEM tire rolling radius.

As I said, I don't know what the offset is on the CTS, but on my 1997 Eldorado I believe it is 42 mm; I would have to spend some time in the FSM to make sure. I have seen replacement wheels with 40 mm that say that they match my offset, and perhaps 2 mm in a tire patch 7 inches (178 mm) wide, perhaps it is good enough -- but I would want a 42 mm offset on the wheels I put on my car, so long as the tires have a 26.6 inch rolling diameter, plus or minus 2% or so.

thanks for the help.

i have a '99 accord that is modified a great deal, and i have played with different offsets and diameters on it. right now i run 19x8s on it with a +40, which is a little off of normal. ive had to roll my fenders, and change the way i drive, but i was ready for that. i under stand how it changes the handeling and all. but the CTS is well capable of fitting up to 22s from what ive seen. and ive also seen a few +38's for the CTS. just no +35's. i know i'll be ok with the clearance around the fender area, just not sure about the inside rubbing the tire once its mounted . the wheel itself clears everything on the inside though.