: Changing Staggered Tire Size to All Same Size



coati
04-12-07, 10:57 AM
This has probably been brought up here somewhere but I was unable to find any definitive information on this.
Does anyone know if there will be any problems going from 235/50/18 fronts & 255/45/18 rears to ALL 255/45/18?
I was in the process of ordering all 255/45/18 size tires for my STS (1SG package) when a mechanic friend of mine says that you have to stick to the current(staggered) tire sizes or else you'll have problems with the ABS & brake lights not working properly.
He said that you have to recalibrate the settings & even then you might still have problems.
According to him he changed tires to all the same size on an '06STS & he encountered those problems & had to stick to the staggered sizes.
He said that Corvettes w/staggered tire sizes are like that too.
I've never heard of this/unaware of this.

1. Is this true?
2. Why did Cadillac stagger the tires on the STS?

Thanks in advance for any input.

BirdJC
04-12-07, 04:01 PM
I can see maybe the ABS sensor being off some because of the overall diameter being changed but the difference between those two tires doesn't seem like it would be enough to do that. I have the 17" rims with staggard tires as well, I wanted to put the 255's all around but was concerned with clearance issues on the front with the wider tire? so basically the question still remains.......can you do this?

STS2002
04-12-07, 04:59 PM
When I had my 05 STS I put 20's on it and 255's all the way around. Never had a problem with them.

coati
04-12-07, 09:16 PM
I spoke with a Cadillac Service Rep this afternoon regarding converting from staggered tire sizes to all the same size.
He said there shouldn't be a problem and that they've done same size tires front & rear on other STS's and it was OK.
As long as they are close in diameter to what's on now.
The fronts (235/50/18) are about 1" more in diameter than the rears
(255/45/18) he said.
They may have to recalibrate the TPMS.
He did express a possible problem with "tire scrub" in the front wheel wells w/255/45/18 in front.
But according to some posters here, they haven't encountered a problem.:)

Caroutisine
04-12-07, 09:39 PM
The Corvette has staggered tires and wheels, I think this would be a problem. However, the 2005 STS (17") has the same size wheels and tires, just slightly wider rims and tires in the rear.

I have snow tires on my stock rims, all the same size (P235/50R17) and have no problems. In the summer, I run the staggered size tires on aftermarket rims (P235/50R17 front, and P255/45R17 rear) and have had no problems switching between the two sets. All I have to do is set up the pressure sensors when I change between each set of tires. This procedure is easy, and covered in the owner's manual.

As far as why Cadillac did this on the STS...I don't know, maybe for the looks more than anything else.

Heavy_Metal
04-13-07, 12:28 AM
Coati

I too have the 2005 1SG but with AWD. I asked the same question on another topic, but nobody replied so I just went ahead and ordered the tires this week.

I looked up the tire specs for the Pilot HX MXM4 on the Michelin's web site and the 235/50/18 fronts are only 0.2 inch larger diameter than the 255/45/18 rears (27.3 and 27.1 inch). Not the 1 inch difference you stated in your post above.

The performance handling package available on the 1SG uses Pilot Sport 255/45/18 for all four wheels. I think this and the break pads are the only difference for the performance handling package. The performance handling package was not available on the AWD in 2005 but it is in 2007.

I also decided to change to the Pilot Sport A/S. I read on that other tire topic that the Pilot Sport A/S is better in wet and light snow than the Pilot HX MXM4. The Pilot Sport A/S product description also seems to clam better sport handling. The Pilot HX MXM4 seems to claim more ride comfort. I decided to go with the grip rather than the soft ride if that really matters. The diameter of the Pilot Sport A/S 255/45ZR18 is 27.2 inch, which is close to the original equipment.

:stirpot:

harryctsv
04-13-07, 04:33 AM
I spoke with a Cadillac Service Rep this afternoon regarding converting from staggered tire sizes to all the same size.
He said there shouldn't be a problem and that they've done same size tires front & rear on other STS's and it was OK.
As long as they are close in diameter to what's on now.
The fronts (235/50/18) are about 1" more in diameter than the rears
(255/45/18) he said.
They may have to recalibrate the TPMS.
He did express a possible problem with "tire scrub" in the front wheel wells w/255/45/18 in front.
But according to some posters here, they haven't encountered a problem.:)
Hi coati,
NO, you will not have any problems to change to 255/45 - 18 on all four corners.
I got the export V8 model and it comes stock with this tire size front and rear, only the V6 model comes with 235 front and 255 rear.

Another point, we have here in Germany on the V8 the CTS V wheels on and they 1/2 inch wider than your wheels - no problems.

I have the Michelin Pilot Sports on, here`s a pic.

http://i80.photobucket.com/albums/j184/harrysxlr/PICT0012-1.jpg

Harry

Dr. Design
04-13-07, 12:38 PM
Hello,
You will not have any problems changing to your desired tire size. As a rule of thumb you should try to stay within +/- .2 of the factory inflated outside diameter. This will keep your speedometer readings accurate. Once you get beyond that .2 the speedo will be off. As for it affecting your ABS... The only time you would affect the ABS would be if you alter the tire size too much. Such as running a 245/30/R20 front and a 265/40/20 in the rear (obviously this is an extreme example). If there is too much of a difference between the front and the rear the wheel speeds would be different, thus causing the wheel speed sensors to react accordingly. The example that was just given has an inflated O.D. difference of at least 1.5". That could be the only way we could see the size of the tires affecting the ABS on these cars.

On our customers cars we run various staggered fitments. The TPSM (Tire pressure sensor monitors) have to be recalibrated by the dealer or us to work with low profile tires. That is due to the fact that they are calibrated to read lower PSI rather than the much higher PSI required in a low profile tire.

Please let us know if there are any questions.
Thank you,


This has probably been brought up here somewhere but I was unable to find any definitive information on this.
Does anyone know if there will be any problems going from 235/50/18 fronts & 255/45/18 rears to ALL 255/45/18?
I was in the process of ordering all 255/45/18 size tires for my STS (1SG package) when a mechanic friend of mine says that you have to stick to the current(staggered) tire sizes or else you'll have problems with the ABS & brake lights not working properly.
He said that you have to recalibrate the settings & even then you might still have problems.
According to him he changed tires to all the same size on an '06STS & he encountered those problems & had to stick to the staggered sizes.
He said that Corvettes w/staggered tire sizes are like that too.
I've never heard of this/unaware of this.

1. Is this true?
2. Why did Cadillac stagger the tires on the STS?

Thanks in advance for any input.

Heavy_Metal
04-13-07, 08:13 PM
Thanks Dr. Design. You have answered my questions too. :thumbsup:

mike sts
11-12-07, 02:58 PM
thanks this helps me also

justgreat
11-15-07, 03:18 PM
one thing to consider when going to a wider tire on the front of any car: there will be a greater tendency to hydroplane in the rain and there will be less traction in the snow.


jackg
06sts6

cguthrie
06-17-08, 11:45 AM
Guys,

I went with the Pilot Sport AS 255/45-18 on all four corners. Felt comfortable for the first time in driving rain yesterday! I'm not hoping for too much in light snow but have seen a huge difference in the rain. Back end sticks, front end doesn't slide. We'll see how long they last.

Also, on a slightly different note got 23.6 mpg running down to FL and back to MD averaging @80 mph.

Very nice ride.

CG
2005 1SG 45K

nflores
01-29-09, 03:54 PM
I just bought an 05 STS with 17" staggered tire sizes, and someone before me had rotated the rear to the front and I have not noticed any problems with clearance.

EChas3
01-29-09, 09:31 PM
According to the VIN Check, my DPO had his dealer rotate the 235/50/18 fronts & 255/45/18 rears. So half of 42,000 miles it was a much worse mismatch than 255/45/18's all around. No problems so far. When I do replace the OEM Michelin's (50,000 maybe more) I'm going 255/45/18's.

Greg00coupe
02-12-09, 09:44 PM
OK I'll confess...... several weeks back I had a flat tire. Took it off and ran it in to be repaired. Thought this is a good time to rotate tires. Pulled out the manual and just glanced at the tire rotation skematic. That's what I followed not knowing the car had different size tires untilI saw this post. Yet I have the fronts on the back and the backs on the front!!! I have maybe 600 miles and no problem.

Going to go to one standard size this fall.

I also have a Corvette. Came with 17 fronts 18 rears. Now has 18/19" wheels. The tire store calculated a lower profile tire to keep the spedo close. Using my Garmin GPS I'm about 2 MPH slower then actual gauge. No big deal. Had the new wheels on the Vette for 6 years and no problems.

Rereading the manual the only reason I have differnt size tires is it has a perfomance package. I hate to say this I love the car but it's not a performance car!!! Gm should have put standard sizes on all 4s.