: About to buy the V - wheel question



csf
11-23-09, 09:39 PM
I am 99 % sure I'm going to buy the STS-V over Thanksgiving weekend. Just wondering will the rear wheels except the factory 18" wheel, or are the caliper/rotor's larger and only a 19" wheel will fit. (Although I will never drive it in snow, I am planning for some winter tires as it gets well below freezing in Maryland, which I assume is too cold for the OEM Pirellis -even on sunny winter days.) Thanks. Craig

csf
11-24-09, 10:09 PM
Boy, over 100 views on my question and not one response. Tough crowd.

jedhead
11-25-09, 03:13 AM
The rear rotors are a little larger. The only way to find out is too jack up the car and try to mount the front wheels in the rear. Maybe no one has tried this before, hence the lack of response.

Bob

Gusteve
11-25-09, 08:39 AM
Do a search in the forum. I'm pretty certain I saw a thread on it a while back (and they did fit). But - don't take my word for it. Even if they do - you know you can't run the same size tires, front and back, right? The back tires will have to be taller to compensate for the shorter 18" rim.

If the whole reason you want to do this is just for snow tires - you can get snows in 19" that fit the rear.

csf
11-25-09, 11:20 PM
Do a search in the forum. I'm pretty certain I saw a thread on it a while back (and they did fit). But - don't take my word for it. Even if they do - you know you can't run the same size tires, front and back, right? The back tires will have to be taller to compensate for the shorter 18" rim.

If the whole reason you want to do this is just for snow tires - you can get snows in 19" that fit the rear.

Thanks for the reply. I have been checking out 18" and 19" winter tires.

I am slightly confused - I thought that if an 18" wheel fit on the rears, and it looks like it will, than 4 identical OEM sized winter 18's would work fine. That is only .6 inch less diameter than the OEM 19's, but losing also of course some width, in the rears. Why do I need a taller tire for only .6 inches? I think I'd prefer 4 matched winter tires.

I am aware from a performance standpoint this is not the best setup, but its only for a few winter months so I can live with it. Don't standard STS's run with all the same wheel sizes? I've never had a car with staggered wheels, but why can't we run the same size front and back? I'm honestly not trying to be difficult or uninformed, but obviously I am missing something? Craig

Heath
11-26-09, 12:04 AM
Do a search in the forum. I'm pretty certain I saw a thread on it a while back (and they did fit). But - don't take my word for it. Even if they do - you know you can't run the same size tires, front and back, right? The back tires will have to be taller to compensate for the shorter 18" rim.

If the whole reason you want to do this is just for snow tires - you can get snows in 19" that fit the rear.

Im sorry but what you said doesnt make any sense. The rear and front factory size tires are almost the exact same overall height, within 1/2". You most certainly can run the same exact tire wheel combo on the rear as the front, given it will bolt up without fitment issues. Ill put mine on the lift tomorrow and swap two wheels and see if it works out.

Gusteve
11-30-09, 09:48 AM
You are correct that there's only a half-inch or so difference in overall diameter front to back. (I think its .63 inch). There's a point where a difference from stock will freak out the ECU and cause issues with traction control. The problem is that no-one knows exactly what that point is.

In this post a guy had rear tires that were .81 inch smaller than stock, and he had issues. http://www.cadillacforums.com/forums/cadillac-sts-v-series-forum/181782-does-different-tire-diameter-affect-abs.html That's guy's post does not say what he had on the front, so assuming the fronts were stock, there rear's were .81 inch smaller than they should be. In my experience with other cars that had staggered set-ups, they would also have traction control issues if the rear size varied too much from the stock size. Something about the ECU detects the rears spinning faster than expected compared to the fronts, (because of the smaller circumference) and assumes they are slipping. Hence - the TCS engagement.

Guys in my Mercury Marauder forum that had this problem just turned off the TCS.

I'm not claiming to be an expert. I'd really like to hear from someone that is running the same size tire all the way around and see if they'd had issues or not.

csf
11-30-09, 11:48 PM
You are correct that there's only a half-inch or so difference in overall diameter front to back. (I think its .63 inch). There's a point where a difference from stock will freak out the ECU and cause issues with traction control. The problem is that no-one knows exactly what that point is.

In this post a guy had rear tires that were .81 inch smaller than stock, and he had issues. http://www.cadillacforums.com/forums/cadillac-sts-v-series-forum/181782-does-different-tire-diameter-affect-abs.html That's guy's post does not say what he had on the front, so assuming the fronts were stock, there rear's were .81 inch smaller than they should be. In my experience with other cars that had staggered set-ups, they would also have traction control issues if the rear size varied too much from the stock size. Something about the ECU detects the rears spinning faster than expected compared to the fronts, (because of the smaller circumference) and assumes they are slipping. Hence - the TCS engagement.

Guys in my Mercury Marauder forum that had this problem just turned off the TCS.

I'm not claiming to be an expert. I'd really like to hear from someone that is running the same size tire all the way around and see if they'd had issues or not.


Thanks for the reply - I did understand all that, just never thought 1/2 inch would set off the T/C. Sure would like to know for sure though. Thanks again.

LITTLEELVISDAN
12-01-09, 08:35 AM
Will the rear 19's fit up front? or they too wide? If they do then we could go 19's matched all the way around. the extra width up front might help with the pushing issue we have on the stock 18's with such a heavy front end. I'd like to be able to run 19's all the way around

Redxped1
12-01-09, 11:49 AM
19's are to wide you will have to run a small spacer for them to work. but the 18's fit in the rear no prob hence why I bought a 18 for a spare tire