Help! Brake upgrade kits and wheel size

[Phrede]

I am about to pull the trigger on ordering new wheels and though I had it nailed down until a call told me that someone had given me some incorrect information. At least they called!

For those of you who have done the upgrade, what is your wheel size including offset? I am getting different stories from vendors. I've ordered the tires 255/45-18 and 285/35-19. on front I can either go 8.5 or 9.5 width if it does not stick outside the fender with an 53 or 56 mm offset. I am thinking an 8.5 with a 53 should clear the caliper and provide the best inside clearance.

On the rear I was hoping to use a 10" wide 19" with a 79mm offset to keep things under the fender. This puts the outer lip within .04" of stock. I may need to re-think that and move to a 56mm offset to allow for 4 piston calipers in the future. The 56mm offset puts the front lip of the wheel almost 1" further out than stock. Maybe a 79mm offset and custom fit spacers? It is easier to grind a spacer than to grind a wheel.

Thoughts? Advice? What have others done with the brake upgrades?

 

[richardyoo]

I know this is not what you want to hear, but "it depends".

It depends on the tire - since different tires have different sidewall profiles... so what width/offset works for one tire may rub with a different tire...

It depends on the brake caliper - some are larger than others... and the profiles are different too... some are curved, some are blocky... and how that fits with the wheel is an issue since the wheel spokes may be curved, etc...

With that said, here are my write ups for brake calipers and wheels... all the info from my install are in these threads....

https://www.xlr-net.com/forums/showthread.php?t=3568

and

https://www.xlr-net.com/forums/showthread.php?t=3811

Good luck.

 

[Phrede]

I know this is not what you want to hear, but "it depends".

It depends on the tire - since different tires have different sidewall profiles... so what width/offset works for one tire may rub with a different tire...

It depends on the brake caliper - some are larger than others... and the profiles are different too... some are curved, some are blocky... and how that fits with the wheel is an issue since the wheel spokes may be curved, etc...

With that said, here are my write ups for brake calipers and wheels... all the info from my install are in these threads....

https://www.xlr-net.com/forums/showthread.php?t=3568

and

https://www.xlr-net.com/forums/showthread.php?t=3811

Good luck.

Thanks for the reply. I anticipate the future brake upgrade to be a bolt on Z06 kit with 6/4 pistons.

I realize there are differences in tire brands, but not so much that at a given size there would be a clearance problem. I would not want to calculate things that tight.

The wheel offset is what I am looking out now in order to try to allow room for the future brake upgrade. I think in the clearance/rubbing issue in the linked posts had more to do with tire selection than offset since a 9.5" width with a 49mm offset actually puts the outer lip farther out than an 8.5" with a 45mm offset. .97" vs .63" from stock respectively. That is why I chose tire sizes that are very close to stock diameters.

 

[richardyoo]

My 285's in the rear are fine... but if you read in my tire thread, you can see that people are convinced I'm nuts when I say they don't rub and thusly only recommend 275's...

With that said, its my understanding that D3 is also doing cars with 295's in the rear on lowered XLR's with no problems as well...

This is why I've concluded its perhaps a sidewall profile issue... the PS2's I have have a pretty flat profile... perhaps some of the other tires of the 285 width rub due to a more domed sidewall? I have no idea - but I can say that they fit my car fine.

Anyhow,I look forward to hearing/seeing how your install goes.

 

[Phrede]

I'm waiting on the big brown truck now. I decided it was time to "just do it" and bought a set of ZR1 replicas. I am reasonably sure things will be OK and I pushed things to the high side of the offset thinking I could always add a little shim if needed. It will be a while until I can tell if the Z06 brake package will fit, but should know by this time next week about the tires and wheels alone.

The calculated change in diameter is less than .7% and the front lip extends no more than .2" further out.

I'll post some pics when I get them mounted.
Front 8.5X18/56mm with 255/45-18 Bridgestone S04 Pole Position
Rear 10X19/79mm with 285/35-19 Bridgestone S04 Pole Position