Tire and Wheel sizes

[gamblingman]

I know this can be a complicated topic, but perhaps someone here can post some easy to understand guidelines for wheel/tire fit for our cars.

I have a base 2005
I have noticed some say you should go with a C5 wheel vs C6? Not sure how different they could be based upon the size?
I would like to move to a 19" x 10" wheel all the way around
most of them have a 65-79mm offset
my guess is that tires would go to a 40 aspect ratio and up to about a 265mm width to maintain speedometer, etc...

Am I well within guidelines or am I crazy?

 

[Wife's XLR]

Aftermarket Wheels-

I know this can be a complicated topic, but perhaps someone here can post some easy to understand guidelines for wheel/tire fit for our cars.

I have a base 2005
I have noticed some say you should go with a C5 wheel vs C6? Not sure how different they could be based upon the size?
I would like to move to a 19" x 10" wheel all the way around
most of them have a 65-79mm offset
my guess is that tires would go to a 40 aspect ratio and up to about a 265mm width to maintain speedometer, etc...

Am I well within guidelines or am I crazy?

I/We have a base 2004....
Not sure if this helps at all or not but recently I just changed my wheels from stock on my wife's XLR to the Centennial wheels of a 2013 Corvette and WE LOVE THEM!!! I ordered them from WCC, West Coast Corvettes in CA and Joseph who works there was a big help. I kept the size to 18" and I used 56 mm as a reference point. IOW, if you buy a wheel and it's offset is 57-59mm, you should be safe with the wheel fitting correctly. It just so happens WCC had the wheels I wanted at 18 x 8.5 x 56mm anyway they're on the car and look FANTASTIC! And by staying with 18" wheel, you won't have to worry about recalibrating the speedometer or computer (not sure which) to compensate for the larger diameter wheel.

On the other hand, if you just like the look of 19" wheels, then all of the above is mute!

 

[ljkrenek]

Wheels

Corvette 245/40ZR18 front 265/35ZR19 rear Love the new aggressive look with a much more accentuated forward rake with the stagger. Ride is a little rough but not so much that it bothers me.

 

[MrSunshine]

I had these AMF 20" forged, monoblock wheels made. Front's are 20x9 et 45 with 255/35/20's & 20x10 et 45 with 275/30/20 Nitto NT 555 G2's. LOVE them! ...No rubbing!

 

[long Tall Sally]

play with this .you just put your stock size In and then the size you are looking for and you can compare. Get too big a rim and the brakes look tiny . You can see how others have moved the tires out a good bit and still kept most of the tire under the fender.

Rim & Tire Size Calculator. Custom Offsets - Wheel-Size.com

 

[Jaxrwild]

235/45 19 front
245/45 19 rear

I am running 19" 235\45 19 fronts 245\45 19 rear

 

[catcottf]

Hi All,
Good afternoon. Just another sunny day in Paradise. Just ordered and received new wheels for my XLR. They look great and I will get a pic posted soon. If you are looking for new wheels I would recommend Factoryreproductions.com. They are great. I worked with Trevor Rhodes and he was a big help. You can reach him at 909-590-5252. I got new 18 x 8.5 chrome wheels, new lugs, new air sensors and delivered for $1,224.
Thanks and have a great day,
Fred

 

[Wife's XLR]

New wheels...

Hi All,
Good afternoon. Just another sunny day in Paradise. Just ordered and received new wheels for my XLR. They look great and I will get a pic posted soon. If you are looking for new wheels I would recommend Factoryreproductions.com. They are great. I worked with Trevor Rhodes and he was a big help. You can reach him at 909-590-5252. I got new 18 x 8.5 chrome wheels, new lugs, new air sensors and delivered for $1,224.
Thanks and have a great day,
Fred

Can't wait to see the new wheels!

 

[catcottf]

Hi All,
Good afternoon. Just another sunny day in Paradise. Here are the new wheels:

 

[HarvesterUT]

I am about to put 19x10 +79 on all four corners. I will be using 25mm spacers as well, so the effective offsets will be +54. Tires will be 275/35/19 (f) and 285/35/19 (r). Based on my mock-ups, these should be OK to run, but final fitment will be the final say on that.

 

[MrSunshine]

The 285/35's 100% WON'T fit. (been there done that.) You need to run a +45 offset in the rear with a t 275/30 at most. Even then, you'll rub. It'll still rub until you rub away some of the inner fender liner & inside, top edge of the fender. A 265/35 or 265/30 will work without rubbing.
I run a 275/30 in the rear on a 20x10 et45 (see pics above in the thread.) 255/35's on 20x9 et45 up front.

 

[HarvesterUT]

The 285/35's 100% WON'T fit. (been there done that.) You need to run a +45 offset in the rear with a t 275/30 at most. Even then, you'll rub. It'll still rub until you rub away some of the inner fender liner & inside, top edge of the fender. A 265/35 or 265/30 will work without rubbing.
I run a 275/30 in the rear on a 20x10 et45 (see pics above in the thread.) 255/35's on 20x9 et45 up front.

I hope to find out this week. Still waiting on wheel #4 to come in. I'm running 25mm spacers F & R, but I'll move up to 30/35mm or wider in the rear if I need more inside clearance. I am not worried about the fender side - I can roll/pull those out as needed. Also, my car currently has 275/40/19 on the stock rear wheels (previous owner). They are HUGE (tall) on the car with no rubbing issues. They also bulge out quite a bit and do not rub on the inside liner. I am purely going off a mock-up I did at my mechanic's shop and some calculations using Willtheyfit.com to get all the dimension changes. I will report back once I get it all lined up.

 

[HarvesterUT]

I remembered the old Motor Trend article about D3's XLR-V, and they ran a 285/30/20. No idea on wheel specs, but they got it to fit. Looks pretty tight whatever it is.
Tuners: 2008 D3 Cadillac XLR-V - MotorTrend

 

[long Tall Sally]

is that the article were they said the wider tires did not help it hardly any and big tires where a waste of money? seems like I remember that. Corvette guys that run high offset wheels then spacers break a lot of wheels an extra long lug nuts snap off.. the load needs to be built into the wheel closer to the centers. Sort of like the skate board wheels the tuners used to run and break. this looks like the tires are too small to me. too much space around the fender openings

 

[HarvesterUT]

is that the article were they said the wider tires did not help it hardly any and big tires where a waste of money? seems like I remember that. Corvette guys that run high offset wheels then spacers break a lot of wheels an extra long lug nuts snap off.. the load needs to be built into the wheel closer to the centers. Sort of like the skate board wheels the tuners used to run and break. this looks like the tires are too small to me. too much space around the fender openings

Correct. The larger wheels did not improve the skidpad performance of the car. Although, going to a larger diameter wheel never improves any vehicle performance - there's a reason why race cars typically run smaller diameter wheels than street cars. I don't think D3 ever did suspension work to their cars, but I could be wrong. I bet you'd see a marked improvement in skidpad with a firmer set of springs. Regardless, this article proves that 285/30/20 tires can fit on the XLR.

As for fender gap, I've noticed that all XLR's sit fairly high up over the rubber. The tires in the photo you linked are only 3.8mm smaller in arch gap versus the stock 255/40/19.

 

[long Tall Sally]

I thought you said you were going to run the 285 35 19 which in most tires at around 25.8 -25.9 are over an inch shorter than the 27 diameter of the stock 255 40 19 . the 20 inch 285 30 is much closer to the 27 and having the wider rim clears some of the suspension more. as to rolling the plastic quarter panes that may be a problem. they break easy before they flex much. If one is only putting the tires on for looks it does not matter that the roll center, the unsprung mass changes and the suspension would need several tweaks to take advantage of the wider contact patch. changing the lower control arm angle lower changes the mag ride sensor calibration so they would need to be adjusted plus the cars already around here drag on parking lot entrances. dropping it another 1/2 inch will make that worse. But if you are going with the 20 inch wheels instead of the 19 as I thought it should not matter .
the

245/45 19 rear that jaxrwild is running adds about 3/8 inch on both sides of the tire and look to me much better without getting too big for the opening. ​

 

[HarvesterUT]

I thought you said you were going to run the 285 35 19 which in most tires at around 25.8 -25.9 are over an inch shorter than the 27 diameter of the stock 255 40 19 . the 20 inch 285 30 is much closer to the 27 and having the wider rim clears some of the suspension more. as to rolling the plastic quarter panes that may be a problem. they break easy before they flex much. If one is only putting the tires on for looks it does not matter that the roll center, the unsprung mass changes and the suspension would need several tweaks to take advantage of the wider contact patch. changing the lower control arm angle lower changes the mag ride sensor calibration so they would need to be adjusted plus the cars already around here drag on parking lot entrances. dropping it another 1/2 inch will make that worse. But if you are going with the 20 inch wheels instead of the 19 as I thought it should not matter .
the

245/45 19 rear that jaxrwild is running adds about 3/8 inch on both sides of the tire and look to me much better without getting too big for the opening. ​

I will be running 285/35/19 which is 682.1mm diameter. Stock size of 255/40/19 is 686.6mm. That is a difference of only 4.5mm or 0.66% speedo error. Ride height will only drop by 2.25mm and arch gap will increase by 2.25mm. The main thing I am worried about is clearance on the inner wheel against the trim that sticks out for the hard top mechanism.

My wheels are effectively 19x10+54 which put the inner barrel 12.1mm closer to the suspension/frame compared to the stock size of 19x8.5+61. If it rubs, I will get a wider spacer to reduce my offset to either +49 or +44. At that point I am worried about contact with the wheel well fender which might need to be rolled under.

 

[long Tall Sally]

send us pictures when you get hem installed

 

[MrSunshine]

You can't pull or roll the fenders on these.

 

[MrSunshine]

I run a 20X10 +45 with a 275/30 in the rear. They rubbed inside & out until I cut away the inner fender liner & wore away the fender lip! No joke. It's as big as can possibly fit. The D-3 setup mentioned earlier rubbed & smoked like you wouldn't believe. They also ditched the mag ride, went to a Z06 rear leaf, then ultimately to coilovers that were so stiff the rear wheels would bounce off the ground when it hit a small bump over 50 mph.
If you decide to cut away the inner fender liner, you'll find sheet metal that protects the retractable roof gear. I let it rub just enough to show me exactly where it needed to be trimmed away. Crude to be sure, but worked great.