Welcome to the Cadillac XLR Forums!

Tire and Wheel sizes

Oh, it's going to be tight for sure. There's only about 11" of room between the inner liner and the outer fender. My 285 tires are 11.4" section width. I might need to upgrade the springs to something firmer to reduce the chance of rubbing. I will also consider trimming away the inner liner and the lip of the fender well. I am hoping to do a test fit before end of week. Will report back.
 
Back from my mechanic's shop. Here are my initial impressions.

Again, I am running:

19x10+54 275/35/19 front
19x10+54 285/35/19 rear

The wheel offset is +79 (C6 base wheel) but I have 25 mm spacers which lower the offset to +54.

The first issue we had was the stock wheel lugs are pretty long - long enough to protrude through the hub-centric spacer and hit the back side of the new wheel. Obviously, this won't work, so we will grind down the tips of the studs about 5mm. This isn't a big deal because the last 10mm or so are smooth and not used for thread contact at all. There's a special drill bit that will shave them down and put a bevel on then similar to stock.

The fronts don't appear to have any fitment issue at all. They will also have plenty of caliper clearance to let me use the Z06 calipers I have.

The rears are going to be TIGHT. We put light torque on the nuts to secure the wheel as best we could on the studs, but again, there was about a 5mm gap from the studs (estimate a +49 offset equivalent). We set the car down on its weight to compress the suspension, but did not drive it for obvious reasons. Even with that, I had about 1 finger of space between the inner barrel/tire and the inner fender liner. This increases my confidence that the inner wheel will clear the plastic trim *just enough*. I have a feeling under full compression, it will rub, so I am prepared to swap stiffer springs in to help alleviate that issue. The outside part of the tire pokes a small bit beyond the fender lip, so that might be an issue under compression - again, stiffer springs will likely be needed. The actual tread was inside the fender, it was the sidewall that stuck out. Tire section width 11.4" and tread width 10.1". Slight negative camber adjustment might also provide more clearance at the penalty of inner fender clearance.

I plan to have everything swapped over by end of next week. Will provide an update then.
 
Last edited:
are you running a spacer or an adaptor. A spacer usually just requires long studs and goes thru the spacer and the wheel were an adapter bolts tot the stock bolts with new studs o nit. Some may call that a spacer also?
 
I am using a bolt-on spacer which bolts to the old hub and has a new set of studs. Alternatively, you could use a slip-on spacer but press-in extended lugs through the actual hub. I believe an "adapter" is typically a type of spacer that also changes the bolt pattern so you can use wheels meant for a different application.
 
ell some companies call the ones that bolt on adaptors even if both have the same bolt pattern. Spacers o nBMW and Porsches use the existing long studs (PORSCHE) or long bolts BMW. If I was going to put bolt on spacers I would have used the adaptors and changed the bolt pattern. thats what I did. Now I have thousands of wheel patterns and offsets to choose from instead of the few for 5x120.
 
True, the 5x120.65 pattern isn't the most common, but I wanted to use original GM parts and keep the modifications "in the family" so to speak. I am using the forged 15-spoke GM "Superalloy" wheels which were a special order option for the base 2008 C6. They look very similar to the OE XLR-V wheels but with more spokes and are polished instead of chrome. Example photo is attached.

Quote from this interesting article: Corvette Wheels Pt 3 of 3 - 1997 to 2009
[FONT=&quot]The ‘08 Corvette had a very nice selection of accessory options for new Corvette buyers.[/FONT][FONT=&quot] The Pratt & Miller-built C6.R racing Corvettes made their mark in road racing history with over 50 victories and 6 class wins at Le Mans. For buyers wanting a unique appearance for their Corvette that salutes the C5-R and C6.R race cars, there was the optional 15-spoke, polished-aluminum wheels, inspired by the successful road racing Corvettes. This was a dealer-installed option.

[/FONT]
00s0s_9TkGY97fwbQ_600x450.jpg
 
Oooooohhh...It's gonna be close!!! Can't wait to see it!
 
I'm getting new wheels and tires for my 2006 XLR-V. The owner of BiggDaddyCaddy recommended that I put 255/40ZR19 96W on the front instead of the stock 235s. What's your recommendation?

 
I ran 255’s on all four corners of my V for a while. Didn’t have any rubbing issues but every once in a while I would get a suspension error code on the DIC. Not sure if I like the look of the thinner tires on the front but that’s my opinion.
 
Michael
Hi, spoke to you in the past about the sway bar.
Just saw this old Post of yours and have a a question if you get a chance.
The XLR I bought came with the same size tires you have in the front.
I have 255/20's all around.
No one I've asked at tire places knows the answer.

Are my speedometer and odometer reading wrong and if so which way and how much ?
Thanks Again, Brad
 
if you are running 255/35/20 the revolutions per miles is almost dead on with most brand tires. there are a few that in that size run a little short but not by more than 2 to 3%. Just check your gps as you drive and see how close it shows. You should be fine .Michael may have more input?/
 
I have 255/20's all around.
No one I've asked at tire places knows the answer.

Are my speedometer and odometer reading wrong and if so which way and how much ?

I assume you mean 255/35/20 size tires which are only 0.01% smaller in diameter than the stock 255/40/19 ones. There is basically no speedometer difference.
 
I'm getting new wheels and tires for my 2006 XLR-V. The owner of BiggDaddyCaddy recommended that I put 255/40ZR19 96W on the front instead of the stock 235s. What's your recommendation?


255/40/19 will fit, but you will probably find the front end to feel more "loose" in the corners because you'll have more sidewall flex. A 255 width tire is not meant for an 8" wide wheel like the V's have in the front. 245 is the widest I would go on an 8" wheel, but you might not drive her hard and care about the wheel flex.
 
I run a 255/35. (on a 9" wide wheel) So width wise, it's no problem. I prefer the 35% aspect ratio over the 40%. "Lower" profile, but not "Looooow" profile. :) On an 8" wide wheel, it'll look a little more aggressive & still work very well.
FB_IMG_1540787059175.jpg
 
Last edited:
The tires the previous owner put on are 255/35/20 all around ...so the speedometer and odometer are reading correctly then ?
Thanks

Correct - there is zero speedo difference compared to stock size. :)
 
I run a 255/35. (on a 9" wide wheel) So width wise, it's no problem. I prefer the 35% aspect ratio over the 40%. "Lower" profile, but not "Looooow" profile. :) On an 8" wide wheel, it'll look a little more aggressive & still work very well.

Well, your wheels are 20" so a 40 aspect would look pretty huge!
 
if you are running 255/35/20 the revolutions per miles is almost dead on with most brand tires. there are a few that in that size run a little short but not by more than 2 to 3%. Just check your gps as you drive and see how close it shows. You should be fine .Michael may have more input?/

I would agree that a 255/35/20 is only going to be off by "maybe" 1mph. In other words, if you're traveling at 76mph (on the speedo) you're actually going 75mph.
Conversely, if you're running a 255/40/20, you may end up going a "bit" slower than what the speedo says, by about 1mph.
In my case, I run a 275/30/20 in the rear & it throws me off by 3mph.
Anyone confused yet??? :confused:
 

Cadillac XLR Forums

Not a member?  Join now!  It's Free!

Learn more about Supporting Membership

Win 2 Supercharged Cadillacs!

Win both supercharged Cadillac Vs!

Supporting Vendors

Taput Tunning LLC

Top Hydraulics

Cadillac XLR Registry

Click here to enter the official Cadillac XLR and XLR-V Registry
Back
Top Bottom