[JustinHEMI]

Originally Posted by Squidget

I was taught that about 4% diameter difference is the limit. Don't know if that's still the rule of thumb these days.

I've read 1.5-2 and this is within that.

I'm likely sticking with OEM. The PS4S looks better on 11" wheel than the Pzeros.

[zero21]

Originally Posted by babym_gen

I wouldn't worry about understeer that much, Porsche runs some crazy staggered setups on the 911 GT3, like 315R/265F.

Stay within the traction limits of the front tires and you will be fine. Add some negative camber to improve surface patch contact.

The Porsche is a rear engine car with a 37/63 weight distribution. This is like comparing apples to bowling balls. Jesus...

[babym_gen]

Originally Posted by zero21

The Porsche is a rear engine car with a 37/63 weight distribution. This is like comparing apples to bowling balls. Jesus...

I explained why I think such 911-like staggered setups make even more sense on ~50/50 front engine cars.
The engine at the rear puts a lot of weight on the rear tires increasing their grip (F = u N as a crude friction model) hence why they have a lot of static understeer. It reduces the chance of losing the back because when you lose it on a rear or mid engine car, it's really hard to catch the spin (due to the pendulum effect and leverage it entails). And with the historical "widow maker" reputation the car garnered, Porsche saw the liability angle and acted accordingly.

All car manufacturers setup their car for understeer for safety/liability reasons but for mid engine and, god forbid, rear engine cars, it's an even bigger issue.

Anyway, applying that setup on a car like the G87 M2, you will get the benefit of increased rear grip with less static understeer (by static, I mean at rest) due to the more balanced weight distribution. The Camaro ZL1 1LE kind of did it with their 325 rear and 305 front.

[spindiesel]

I’m running a 285/30r20 up front and a 305/30r20 rear all on 20x10.5 wheels. Added a 10 mm rear spacer. No rubbing, drives great. It’s def a bit more sensitive to steering inputs, but on a warm day it’s very planted and precise. I do have a Nitto NT05 on the rear ……

[M Division]

Originally Posted by JustinHEMI

When I'm done with these Pzeros, I'm probably going to want to go to 295/30/20 in the rear while staying OEM size up front.

Any concerns with that? I think the 285-295 increase should be negligible in terms of changing dynamics, but wanted to see if I should be thinking about bumping the front from 275 to 285 as well.

Thanks!

(Not interested in 305s)

Unless you're changing rims sizes and fronts you will probably run into trouble with front to rear diameter ratios.

Assume you're trying to get more launch from the rears rubber? The difference would be so minimal and potential ratio issues would probably make it more trouble then it's worth.

Simply switching to stickier rubber on factory sizes would be the best bang for buck.

[JustinHEMI]

Originally Posted by M Division

Unless you're changing rims sizes and fronts you will probably run into trouble with front to rear diameter ratios.

Assume you're trying to get more launch from the rears rubber? The difference would be so minimal and potential ratio issues would probably make it more trouble then it's worth.

Simply switching to stickier rubber on factory sizes would be the best bang for buck.

I DID change rim sizes hence the question. I'm at 19x10 front and 20x11 rear. The fronts are fine from a "stretch" perspective, but the stock Pzeros look like ass on the 11" rears.

If I bump the fronts to 285/35/19 and the rear to 295/30/20, they're both increasing the same percentage according to the screenshots I posted early in the thread. The speedo is pretty close too, reading about 1mph low according to those calculators.

I am really only trying to solve a cosmetic issue, but trying to keep the balance of the car. I think these sizes on these wheels will be fine based on all the calculators.

Now, I've also read that the PS4S in OEM size may not be stretched as bad as the Pzeros on an 11" wheel, but I don't know for sure.

Here's the rear stretched,




Here's the front.





Baby Gem seems to think keeping the OEM front size and going to the 295 in the rear would be OK too. Probably would be.

[KC87ZB]

Keeping the OEM front with wider rear would have a tendency to increase understear. On a rear drive car I don’t see that as a huge issue and if you know it going in then you know what to expect. I’d probably go up one size on the front.

From an electronics/traction control perspective you want to keep front and rear rolling diameter difference about the same as stock.

Diameter difference is especially a concern on xdrive cars so watch who you get advice from and what their perspective is.

[JustinHEMI]

Originally Posted by KC87ZB

Keeping the OEM front with wider rear would have a tendency to increase understear. On a rear drive car I don’t see that as a huge issue and if you know it going in then you know what to expect. I’d probably go up one size on the front.

From an electronics/traction control perspective you want to keep front and rear rolling diameter difference about the same as stock.

Diameter difference is especially a concern on xdrive cars so watch who you get advice from and what their perspective is.

Yeah I think I'm settled on going up to 285/35/19 and 295/30/20 when it's time to replace.

PS4S are available in those sized, though not BMW* variety. I doubt I'd ever notice that difference.

[M Division]

Originally Posted by JustinHEMI

Yeah I think I'm settled on going up to 285/35/19 and 295/30/20 when it's time to replace.

PS4S are available in those sized, though not BMW* variety. I doubt I'd ever notice that difference.

The BMW* and standard PS4s are actually quite different. You may even be more likely to notice the compound difference over the slightly increased contact patch of the wider tyre..

https://youtu.be/COA630Juf_U

[Tag]

Originally Posted by JustinHEMI

Yeah I think I'm settled on going up to 285/35/19 and 295/30/20 when it's time to replace.

PS4S are available in those sized, though not BMW* variety. I doubt I'd ever notice that difference.

Wait for the PS5S, problem solved.

[JustinHEMI]

Originally Posted by M Division

The BMW* and standard PS4s are actually quite different. You may even be more likely to notice the compound difference over the slightly increased contact patch of the wider tyre..

https://youtu.be/COA630Juf_U

No I know they're different, I'm saying I doubt *I* could feel the difference.


That being said, I see Porsche also has a compound. I wonder how it compares to BMW.

[M Division]

Originally Posted by JustinHEMI

No I know they're different, I'm saying I doubt *I* could feel the difference.


That being said, I see Porsche also has a compound. I wonder how it compares to BMW.

I wouldn't be surprised if the Porsche compound is closer to the BMW but that's pure speculation. My 992 runs Bridgestones and they're actually fantastic, but it is a 4S so it has ridiculous grip in all conditions.

[bernard1414]

Originally Posted by M Division

I wouldn't be surprised if the Porsche compound is closer to the BMW but that's pure speculation. My 992 runs Bridgestones and they're actually fantastic, but it is a 4S so it has ridiculous grip in all conditions.

Which Bridgestone's came on on your 992?

[Charley135]

Originally Posted by JustinHEMI

I am really only trying to solve a cosmetic issue, but trying to keep the balance of the car. I think these sizes on these wheels will be fine based on all the calculators.

why dont you just install spacer and keep oem size?

[M2siast]

Originally Posted by Charley135

why dont you just install spacer and keep oem size?

He has new/wider wheels.

[VIERsr]

Sorry to chime in on this thread now that your car is injured, but I'm having the same dilemma.
I would like to put on the 10.5"/11" Edelweiss rims, but I would also like to keep the OEM tire sizes, and I'm afraid that the rear 285's will be too stretched out on the 11", compromising both aesthetics and performance.
I will see what tires my car will come with, it seems that Michelin tires are a bit wider, although Michelin recommends 9.5-10.5 as the rim width range for 285/30.
285/35-19 and 295/30-20 would be the best route for 10.5/11 rims, but I don't want to put more rubber on the ground and the 285/35 seems too "fat."