275/30r20 and 295/30r20 PS4S on Type 666 with M Performance HAS

[PLZ_M3]

No. Theoretically you could get a 285 on the front, but that's not the issue. The problem you're talking about has nothing to do with the width of the tire, but rather the HEIGHT of the tire. The distance from the center of the axel to the road surface needs to be the same on the front and back of the car. Consider cars that have 19" front rims and 20" rear rims - the aspect ratio varies on these cars front and rear tires such that the front tire is TALLER than the rear tire to keep circumference (and of course, the outer diameter) the same from front to back. Aspect ratio changes only when rim width changes.

Do you have a good tuning shop? They should be walking you through this process. Send me some more details and I'll see what blanks I can fill in for you.[/QUOTE]

So even though the circumference is different between the 275/30/20 (26.5" diameter) and 295/30/20 (27" diameter), those sizes are fine? A shorter diameter of the front wheel would mathematically make the circumference smaller than the rear tire w/ a 27" diameter, no?

I'm in the same boat trying to decide between the Cup 2's and the 4S's. If you're saying the tire circumference should be the same from front to rear, wouldn't the 245/35/20 Cup 2's (26.8" diameter front) have a better rolling circumference paired w/ the 295/30/20 (27" diameter rear)?

[whoop_ass]

Originally Posted by PLZ_M3

No. Theoretically you could get a 285 on the front, but that's not the issue. The problem you're talking about has nothing to do with the width of the tire, but rather the HEIGHT of the tire. The distance from the center of the axel to the road surface needs to be the same on the front and back of the car. Consider cars that have 19" front rims and 20" rear rims - the aspect ratio varies on these cars front and rear tires such that the front tire is TALLER than the rear tire to keep circumference (and of course, the outer diameter) the same from front to back. Aspect ratio changes only when rim width changes.

Do you have a good tuning shop? They should be walking you through this process. Send me some more details and I'll see what blanks I can fill in for you.

So even though the circumference is different between the 275/30/20 (26.5" diameter) and 295/30/20 (27" diameter), those sizes are fine? A shorter diameter of the front wheel would mathematically make the circumference smaller than the rear tire w/ a 27" diameter, no?

I'm in the same boat trying to decide between the Cup 2's and the 4S's. If you're saying the tire circumference should be the same from front to rear, wouldn't the 245/35/20 Cup 2's (26.8" diameter front) have a better rolling circumference paired w/ the 295/30/20 (27" diameter rear)?[/QUOTE]

Here is a the link to the guys that have tried the PSC2 on 20"
https://f80.bimmerpost.com/forums/sh...highlight=psc2

I used the N0 spec 245 and it worked a charm

[PLZ_M3]

Originally Posted by whoop_ass

So even though the circumference is different between the 275/30/20 (26.5" diameter) and 295/30/20 (27" diameter), those sizes are fine? A shorter diameter of the front wheel would mathematically make the circumference smaller than the rear tire w/ a 27" diameter, no?

I'm in the same boat trying to decide between the Cup 2's and the 4S's. If you're saying the tire circumference should be the same from front to rear, wouldn't the 245/35/20 Cup 2's (26.8" diameter front) have a better rolling circumference paired w/ the 295/30/20 (27" diameter rear)?

Here is a the link to the guys that have tried the PSC2 on 20"
https://f80.bimmerpost.com/forums/sh...highlight=psc2

I used the N0 spec 245 and it worked a charm[/QUOTE]

I've seen that thread, but it still had me curious about the rolling diameter since I've seen a few times the front diameter should match the rear. And it seems that even the stock PSS are 1/2" shorter in diameter in the front versus the rear. 245/35/20 and 295/30/20 Cup 2s or RE71Rs it is. Thanks.

[TayF80]

Originally Posted by FourPtDrift

Considerably! And the car is much "pointier" from center, as well. Hook-up, greatly improved - an absolute must before any tuning to the car.



Yes - that's really a myth. What BMW wants to do is mitigate liability by dialing in understeer. The OE aspect ratio does exactly that.

The PS4S has an extremely strong side wall and the turn in with my 275/30r20 fronts is fantastic. Excellent communication to the fingertips and butt.

Can't say it enough - this is how the car should have been setup from the start.

Could the sidewall go to a 35 or even 40 without rubbing on stock suspension with the Comp Package?

[chujk1985]

anyone running this setup on an m3?

[einscot]

Originally Posted by chujk1985

anyone running this setup on an m3?

Don't. I tried, and your fronts will rub your fender liner. I had to stick with the 265s in the front (thankfully a forum member bought my 275s that i couldnt use). Even the 265s cut it close.

[chujk1985]

Originally Posted by einscot

Don't. I tried, and your fronts will rub your fender liner. I had to stick with the 265s in the front (thankfully a forum member bought my 275s that i couldnt use). Even the 265s cut it close.

So are you running 265/30/20 and 295/30/20 PS4S? Is this an ok setup without issue? Any drop or spacers? Pics?

[Remonster]

Originally Posted by PLZ_M3

No. Theoretically you could get a 285 on the front, but that's not the issue. The problem you're talking about has nothing to do with the width of the tire, but rather the HEIGHT of the tire. The distance from the center of the axel to the road surface needs to be the same on the front and back of the car. Consider cars that have 19" front rims and 20" rear rims - the aspect ratio varies on these cars front and rear tires such that the front tire is TALLER than the rear tire to keep circumference (and of course, the outer diameter) the same from front to back. Aspect ratio changes only when rim width changes.

Do you have a good tuning shop? They should be walking you through this process. Send me some more details and I'll see what blanks I can fill in for you.

So even though the circumference is different between the 275/30/20 (26.5" diameter) and 295/30/20 (27" diameter), those sizes are fine? A shorter diameter of the front wheel would mathematically make the circumference smaller than the rear tire w/ a 27" diameter, no?

I'm in the same boat trying to decide between the Cup 2's and the 4S's. If you're saying the tire circumference should be the same from front to rear, wouldn't the 245/35/20 Cup 2's (26.8" diameter front) have a better rolling circumference paired w/ the 295/30/20 (27" diameter rear)?[/QUOTE]


Front and rear tire circumference doesn't necessarily need to be the same and actually should not be exactly the same on the F8x M3/M4. On AWD vehicles you need to keep diameter the same to prevent premature wear on the AWD system, a lot of people know this and think it is true on all types of vehicles. On any type of vehicle, you want to stay within a 2-3% of the factory circumferences because that's the setup that the stability control systems are programmed around, deviating too far has unpredictable and undesirable effects.

The factory M3 tires are 0.5" larger diameter in the rear vs. the front, 26.3" front vs 26.8" rear, and if you want to deal in circumference that would be 82.6239" front and 84.1947 rear. Ideally, you want to stay at or close to this same ratio of front to rear tire diameter (or circumference).

I've noticed an increasingly popular trend in the auto industry towards a larger rear tire diameter, non-M BMWs have always had a very slightly taller front tire (for example: my previous 335is had 25.2" front and 25.0" rear tires) but M3s tend to have the larger diameter rear tire, they run the same aspect ratio front and rear with a wider rear tire. I've also noticed more sports cars coming with staggered wheel diameters, M3 CS 19" front and 20" rear, 991 GT3 RS 20" front and 21" rear, etc. I don't know enough about vehicle dynamics to know why this is becoming more common but I've started seeing it all over the place.

[einscot]

Originally Posted by chujk1985

So are you running 265/30/20 and 295/30/20 PS4S? Is this an ok setup without issue? Any drop or spacers? Pics?

i don't have any spacers on mine and i'm at the lowest MP HAS suspension setting. but even before I added that suspension the 275s were too big. 265 is the widest in the ps4s on an M3.

[chicagoshark]

Originally Posted by einscot

i don't have any spacers on mine and i'm at the lowest MP HAS suspension setting. but even before I added that suspension the 275s were too big. 265 is the widest in the ps4s on an M3.

Im also curious about the 265/295 combo in the PS4S. Would love to do 275, But I've heard rubbing is an issue as it looks like you are confirming. However my car is stock

[einscot]

Originally Posted by chicagoshark

Im also curious about the 265/295 combo in the PS4S. Would love to do 275, But I've heard rubbing is an issue as it looks like you are confirming. However my car is stock

i changed rubber before i went soft...

wait. what i meant was that even before i lowered on MP HAS, the 275 rubbed and the 265 were still cutting it close

[knightarmor]

Looks great man thanks for the pics and info!

[FrozenGT]

Thanks OP! I have 2020 ZCP HE. I can honestly tell you the stock tire size looks the best and it also has the least amount of chance of rubbing also I would not upsize just for the fact that you lose turn-in feel.

We have to learn how to accelerate and you won't break traction…285s are massive amounts of tire.

Thanks for doing this! I was wondering the same thing

[FourPtDrift]

Originally Posted by FrozenGT

Thanks OP!

I have 2020 ZCP HE. I can honestly tell you the stock tire size looks the best

Thanks for "honestly" sharing your OPINION as to what "looks the best."

The fact remains, as I previously stated, BMW clearly, intentionally undersized the tires on the F8X platform to induce understeer as a liability mitigator. No "no-compromise" performance setup EVER stretches a sidewall. And so if the "look" you want, is that of a real performance solution - and you want to achieve REAL performance gains, the setup I first tested out and validate on this forum back in 2018 - and continue to use to this day on my 2020 F83 (my 3rd F8X car), is the way to go.

and it also has the least amount of chance of rubbing

This is called "introducing FUD" into the conversation and is not called for. Fear, Uncertainty and Doubt. I have deployed my approach on two F83's and one F82. I have tracked these cars and driven them hard for 10's of thousands of miles, with no rubbing, ever. Not even close. And, to boot, the F82 WAS sitting somewhat lower than stock as it was riding on the BMW M Performance HAS.

also I would not upsize just for the fact that you lose turn-in feel.

More ill-informed FUD.

Upsizing to a sidewall that is plumb with the tread surface does NOT diminish turn-in feel - certainly not on the 4s. Upsizing where the sidewall is no longer plumb with the tread surface and is bowed out WILL reduce turn-in feel. That is NOT what is caused with the solution as presented by me earlier in this thread.

We have to learn how to accelerate and you won't break traction…

"We" as in me, has over two decades of HPDE experience including nearly 10 years sponsored by several manufacturers.

The amount of deflection issues that exist within the F8X chassis/suspension setup are considerable. This is why there is such tremendous change between the consumer oriented F82's (regardless of version, including the GTS), and the F82 GT4. Sorting out the F82 by bringing it up to GT4 spec is the best approach, but very expensive. Increasing the contact patch, with a proper balance front to back, isn't nearly as good but it DOES help, tremendously over the stock setup.

And it looks the way a performance rim and tire package SHOULD look.

285s are massive amounts of tire.

As they say in M Town - Too much is just right.

Thanks for doing this! I was wondering the same thing

Again, you're welcome - but please - don't introduce FUD into a technical conversation. It's not helpful for those who really want to know how to solve a problem. It is why I created this thread - and supported the post with photos, including images detailing internal clearances as well.

[FrozenGT]

Originally Posted by FourPtDrift

Thanks for "honestly" sharing your OPINION as to what "looks the best."

The fact remains, as I previously stated, BMW clearly, intentionally undersized the tires on the F8X platform to induce understeer as a liability mitigator. No "no-compromise" performance setup EVER stretches a sidewall. And so if the "look" you want, is that of a real performance solution - and you want to achieve REAL performance gains, the setup I first tested out and validate on this forum back in 2018 - and continue to use to this day on my 2020 F83 (my 3rd F8X car), is the way to go.

This is called "introducing FUD" into the conversation and is not called for. Fear, Uncertainty and Doubt. I have deployed my approach on two F83's and one F82. I have tracked these cars and driven them hard for 10's of thousands of miles, with no rubbing, ever. Not even close. And, to boot, the F82 WAS sitting somewhat lower than stock as it was riding on the BMW M Performance HAS.

More ill-informed FUD.

Upsizing to a sidewall that is plumb with the tread surface does NOT diminish turn-in feel - certainly not on the 4s. Upsizing where the sidewall is no longer plumb with the tread surface and is bowed out WILL reduce turn-in feel. That is NOT what is caused with the solution as presented by me earlier in this thread.

"We" as in me, has over two decades of HPDE experience including nearly 10 years sponsored by several manufacturers.

The amount of deflection issues that exist within the F8X chassis/suspension setup are considerable. This is why there is such tremendous change between the consumer oriented F82's (regardless of version, including the GTS), and the F82 GT4. Sorting out the F82 by bringing it up to GT4 spec is the best approach, but very expensive. Increasing the contact patch, with a proper balance front to back, isn't nearly as good but it DOES help, tremendously over the stock setup.

And it looks the way a performance rim and tire package SHOULD look.

As they say in M Town - Too much is just right.

Again, you're welcome - but please - don't introduce FUD into a technical conversation. It's not helpful for those who really want to know how to solve a problem. It is why I created this thread - and supported the post with photos, including images detailing internal clearances as well.

If you were going to increase your tire size you then need to purchase proper wheels that can hold that amount of tire size. I do not like putting anything above a 285 on a 10 inch wheel those who choose to more power to them.



And I don't think anyone disagreeing with you about upsizing and having a proper tire contact patch. I also have a M2 competition with the M performance suspension setup-corner balanced and I have tons of grip on the stock tire size.

But overall I just feel that if you want to increase your front and rear tire sizes you should upsize your wheels for 295 should have an 11 inch wheel a 9 1/2 to a 10 inch should run a 275 upfront