Tried a search and came up dry. I recently purchased a 2006 sts 3.6 and noticed that the vehicle called for two different size tires, {235/50r/17, 255/45r/17} is it necessary when buying new tires that you purchase the same size or can you go with the 235/50r/17, it is very confusing. Is there a reason for this. Please explain, I do not understand, never ran in to this. Thank You

if it showing 2 different sizes, it because of the staggered wheel. ur rear wheels are larger then the front. to be sure, just look at the tires on the rim themselves and u'll see.

It's true,. the rears are bigger than the fronts and this was Cadillac's way of matching BMW, Lexus and the like. When buying new tires you can go with just one size, the smaller or bigger, then you can rotate them in any configuration as long as they're not 'directional' tires. It's no big deal, so when you're ready to replace the tires just go with what's on there now.

sorry i must have presented my problem the wrong way. i am concerned about buying the same size all around or staying with a staggered pair the smaller size being the prevalent size thank you for your reply.

u cant buy the same tire for staggered, u must replace them how they are. tires are designed to fit circumference and diameter and width of a wheel. the fronts are 7" or 7.5" width and rear is 8" the tire size on the back will be to large, width wise to fit on the front.

u cant buy the same tire for staggered, u must replace them how they are. tires are designed to fit circumference and diameter and width of a wheel. the fronts are 7" or 7.5" width and rear is 8" the tire size on the back will be to large, width wise to fit on the front.

Not true! I bought my 2005 V8 1SF used with 235/50ZR17 Goodyears on all four, staggered rims (later discovered that both, wide rims were mounted on right side to boot) and ran them that way for a year before I replaced all four with 235/50ZR17 Michelins. No problems of any kind (and I drive it pretty hard). Now weird tire wear, alignment issues, traction control, nothing. I did have them put the wide rims on the rear for grins.

Yes, the 255/45ZR17 has 20mm wider tread, but the tire diameters/circumference are the same on either rim i.e., 235/50ZR17 = 255/45ZR17 with a little extra tread width. The "rear" rims are only 1/2" wider than the "front" rims (1/4" each left/right cross section) which only slightly deflects the sidewall, but not enought to affect the tire. If you check out tire on Tirerack.com, you'll find that tires are rated for minimum and maximum rim widths. The only down side to using the narrower tires on the wider rims is that rim may be slightly more susceptible to curb rash.

I would think that the extra tread on the rear end would only be benificial with VERY spirited drving under ideal conditions with a big honking STS-V motor. My "puny" V8 doesn't need 255s, 235s do rather nicely and I can rotate them!

i would double check the rims. but i dont trust that statement. im sorry but the tires are designed for different thickness. now u have have tires that will give you more tire wall ,then yes the side can be changed, but then your gonna set off ur speedo. best off talking to professional inless ur going to change ur own tires urself.

Useful site: http://www.1010tires.com/TireSizeCalculator.asp

Stock Tire - 255/45R17
vs. 235/50R17

Section Width: 10.03 in 255 mm
Section Width: 9.25 in 235 mm

Rim Diameter: 17 in 431.8 mm
Rim Diameter: 17 in 431.8 mm

Rim Width Range: 8 - 9.5 in
Rim Width Range: 6.5 - 8.5 in

Overall Diameter: 26.03 in 661.16 mm
Overall Diameter: 26.25 in 666.75 mm

Sidewall Height: 4.51 in 114.55 mm
Sidewall Height: 4.62 in 117.34 mm

Radius: 13.01 in 330.45 mm
Radius: 13.12 in 333.24 mm

Circumference: 81.77 in 2076.9 mm
Circumference: 82.46 in 2094.4 mm

Revs per Mile: 799.0
Revs per Mile: 792.3

Speedometer: 60 mph 100 km/h
Speedometer: 59.4 mph 99.1 km/h

Speedometer Difference: n/a
Speedometer Difference: 0.845% too slow

Diameter Difference: n/a
Diameter Difference: 0.84%

...so not *exactly* the same, but all in all pretty close (-0.6 MPH, +6.7 RPM). I believe that their recommendation is not to exceed OEM by 3%. As long as the manufacturer rates the tire/rim combination, you're golden (they wouldn't dare rate an unsafe combination). And I do have my tires professionally mounted (don't we all?).

so that just shows the difference. problem with tires that are so small width wise it can become unseated easy and cause a blow out. and by blow out i mean where the tire becomes unseated where the wheel's lip is. over side u might be ok, but u'll cause awkward pressure on the tire wall from the tire being larger then the wheel. i would just highly recommend if ur sticking with ur stock wheels to go with the correct stock tire sizes. to fit the wheel correctly and to not offset ur speedo.

Buy three extra rims (front size), and sell two of your orig ones. Use third for a real spare. Then buy 4 matching tires. Use one orig for spare if you like, or buy a 5th tire.

This will allow you to rotate tires every 5,000 miles or so. Everyone lives happily ever after.

Buy three extra rims (front size), and sell two of your orig ones. Use third for a real spare. Then buy 4 matching tires. Use one orig for spare if you like, or buy a 5th tire.

This will allow you to rotate tires every 5,000 miles or so. Everyone lives happily ever after.

Good advice! Maybe he can just find someone to trade? Someone out there must be nuts enough to want 255/45ZR17s on all four corners!

Good advice! Maybe he can just find someone to trade? Someone out there must be nuts enough to want 255/45ZR17s on all four corners!

ya who wants the small wheels? heh tho the size widths not that much.

1/2 Inch wheel width - no big deal. 1 Inch... Maybe...

The 17" staggered wheels pose a good question. I'd probably go with the larger tire and put the bigger wheels on the back. I'd rotate occasionally but put 2/3 of the miles on as described.

I may be wrong but I'm not uncertain!

1/2 Inch wheel width - no big deal. 1 Inch... Maybe...

The 17" staggered wheels pose a good question. I'd probably go with the larger tire and put the bigger wheels on the back. I'd rotate occasionally but put 2/3 of the miles on as described.

I may be wrong but I'm not uncertain!

I wouldnt chance it. i like drive quick at times and feeling the car take corner well, anything that was specific for that rim is a chance not worth taken. He is better sticking to stock specs. When he rotates the wheels he will till have to move the wider wheels to the front which could throw the system off. seeing it is setup to have wider wheels in the rear by factory defaults.

As others have said (maybe in a different way) the issue will be running the 255's on a narrower wheel than what is recommended. I know recommended is just that, but there's a reason for those wheel width specifications. The contour of the tire is affected by the mounting width and therefore won't be in a normal design range. Will you have problems?--probably not. Will you notice it?--only if you are sensitive to handling and traction issues. It just won't be optimized.

I have an 07 STS 1SG with staggered tires and the rims are the same width on both front and back, just the tires are different size. So in this case you could put the smaller or larger size tires on all four rims.

I have an 07 STS 1SG with staggered tires and the rims are the same width on both front and back, just the tires are different size. So in this case you could put the smaller or larger size tires on all four rims.

that doesnt sound right. staggered wheels are different widths for the wheels. you can put different tires sizes on the same 1 wheel, and usally you have different side walls,but staggered wheels means the wheels are the same for the front but different to the ones in the back. did you measure all 4 wheel widths to make sure they didnt put ur bigger wheels on one side, or that u even where given staggered wheels.

I agree--something doesn't sound right. On staggered 17" cars, the front should be 7.5 and the rear 8.0. Now there does seem to be some difference in marking or identifying the wheels. Some will have the width specified on the inboard side of the hub, while others will say "rear only" You may want to check your oprion codes to see if it originally came with staggered tires.

I agree--something doesn't sound right. On staggered 17" cars, the front should be 7.5 and the rear 8.0. Now there does seem to be some difference in marking or identifying the wheels. Some will have the width specified on the inboard side of the hub, while others will say "rear only" You may want to check your oprion codes to see if it originally came with staggered tires.

Yah, remove the center cap and you'll find [REAR ONLY] stamped on the wider rims and [GM] stamped in the same place on the narrower rims. That's how I figured out that both [REAR ONLY] rims were on the right side and that's how I confirmed the stealership moved them to the rear.

The tread circumference of the tire is fixed no matter how far you deflect the sidewall (within reason, steel belts don't stretch, eventually you'll deform the round tire into an oval). Deflecting the the 235s and extra quarter inch is virtually irrelevant. I would be surprised if anyone on this forum, especially myself, could tell the difference (unless maybe you've got a super-charged V or you're just insane). How much do you think the sidewall deflects under heavy lateral loads anyway? More than a quarter inch! If any tire were to break the bead under any lateral loads we can put on them (short of physical contact with an obstacle) before the tire loses traction, we're all in big trouble! These aren't racing slicks, they're passenger car tires. Yes 255s will give you more lateral grip, but will you really use it? When you panic snap turn the wheel, will 255s (even w/stability control) keep you from spinning out? I can only speak from my experience with 235s on staggered rims, and I vote "Yea".

I was going through the same thing when I was trying to find snow tires for my 05 RWD STS. I have the staggered setup (235/50/17 front and 255/45/17 back). I called Cadillac headquarters and it was confirmed by my local dealer that you can (and they recommend) that you run the 235/50's all around. I bought some Blizzak LM-22's for the winter and will put the Michelins back on in the summer. My rims are also 7.5in. front and 8in back. They do have the 'rear only' stamp on the larger (8in) rims . The 235's fit fine and work well so far. Once the snow flies I'll know how good they really are but I expect them to perform well. I'll probably only run the 235's all around for the winter and go back to the original staggered config. all other times since this is how it was designed.

that doesnt sound right. staggered wheels are different widths for the wheels. you can put different tires sizes on the same 1 wheel, and usally you have different side walls,but staggered wheels means the wheels are the same for the front but different to the ones in the back. did you measure all 4 wheel widths to make sure they didnt put ur bigger wheels on one side, or that u even where given staggered wheels.

I know my 2006 1SG has staggered tires on identical 18" rims. The circumfrance of the two sizes of tires are very close.

I think the 2007 1SG is the same.

I know my 2006 1SG has staggered tires on identical 18" rims. The circumfrance of the two sizes of tires are very close.

I think the 2007 1SG is the same.

that still doesnt sound right. i'd just randomly quick cadillac about that and see if they agree to that statement. and if they dont then u can say hey, why does mine like that. staggered wheels are different thickness.

It is what it is.

doesnt make sense for cadillac to charge so much money and keep same width wheels but charge u half a grand more for different size rear tires. but in the end for this its gonna be what ever the person wants to buy and what ever recommendations the pro says. i just know what i'd be doing.

Well this was the thread that made me curious enough to investigate. I have an 05 with the 1sg 18" wheels.

I pulled the center caps, nothing stamped on there. Surely if I jack it up and pull off the wheels there will be some dimensions stamped on the back side of a spoke???? Nope lots of numbers but they were all identical between the rear and front wheels. I did confirm the wheel sizes for all 4 wheels by careful measurement.

What concerns me is if you go to get new tires how can you be certain the tire store gets the right rim and tire combo?? You have to be a very proactive consumer for something like that. Heck last time I had tires put on the 00 STS they left the lug caps loose and I found them all over the street!!!

I had 17" staggered tires. I split the difference, put P245-45-17's all the way around which is a very common size. Slightly different diameter than stock, but made very little difference in speedometer reading. Still going after over 20,000 miles and I rotate them regularly.

after all is said and done I think whoever [at cadillac] came up with the idea of wider tires on the rear did so for marketing. Wider tires on the rear have two reasons for being there 1. More rubber on the ground for better traction,2 softer ride. There are too many STS's with same size tires all around that have not had any negative effects on ride, handling, or any kind of suspension problems. If any have:mad2: had any such problems, speak now or forever hold your peace!:mad2:

... If any have:mad2: had any such problems, speak now or forever hold your peace!:mad2:

Sounds reasonable in theory, but I don't have the CASH to swap between staggered and non-staggered just to see how it handles on the same car. Mine came with 4x235/50R17, and when I got the car at 30K miles it handled like driving on ice skates after a deep freeze anytime the road was moist.

I admit I'm curious about differences in real world handling between staggered and non, but for now I'm happy and not sliding all over the road with my Blizzak LM22s on all 4 corners.

...it handled like driving on ice skates after a deep freeze anytime the road was moist.

So do you think this was more about the tread design/compound or the tread width?

So do you think this was more about the tread design/compound or the tread width?

Tread? It was supposed to have tread?? ohhhh

Lack of tread + compound more likely the issue.