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[pbonsalb]

You are right -- in this particular case. My mistake -- but not necessarily in all cases. Here, the front is turning 8 fewer revolutions per mile than the rear because it is 1/4 inch larger diameter than the rear. Push the width a little more, however, and the wide 30 series indeed does become larger diameter than the narrow 35 series. For example, a 295/30/19 about equals a 255/35/19 and a 305/30/19 is in fact taller than a 255/35/19. This is because aspect ratio is a percentage of width.

But my main point was that the difference in rpm front to rear on the GTS is opposite that of the regular M3.

[DirtyJersey]

Originally Posted by Ilia@IND

I don't mean to derail this thread, but what is your end goal in using the smaller sidewall tire? Are you looking for a more aggressive appearance? Maybe there's another way of meeting your goal, without using a very short tire, depending on what you're looking to achieve.

My goal is the improvement of looks alone. Never was a fan of such thick sidewalls. I very much perfer the look of 30 profile and am extremely satisfied with how they came out with the zcp wheels. So much so that ill take it even if it sacrifices some driving stability. But at this point it might be a bit much.

An update: turning off dsc doesnt really yeild much of a difference. Which is odd if dsc is in fact intervening. Also just yesterday some weird things happpened when i was driving with the car seemingly lurching a couple times while i was steadily driving along. Right after, driving stability lights came on telling me to reduce speed and avoid hard braking. It quickly went out automatically a few mins later.

I got to figure this out. Next is oem test then figuring if i go with the 30s in the front, if thatll correct things.

Not sure if the dinan springs may be playing a role too.

[elh0102]

Originally Posted by DirtyJersey

My goal is the improvement of looks alone. Never was a fan of such thick sidewalls. I very much perfer the look of 30 profile and am extremely satisfied with how they came out with the zcp wheels. So much so that ill take it even if it sacrifices some driving stability. But at this point it might be a bit much.

An update: turning off dsc doesnt really yeild much of a difference. Which is odd if dsc is in fact intervening. Also just yesterday some weird things happpened when i was driving with the car seemingly lurching a couple times while i was steadily driving along. Right after, driving stability lights came on telling me to reduce speed and avoid hard braking. It quickly went out automatically a few mins later.

I got to figure this out. Next is oem test then figuring if i go with the 30s in the front, if thatll correct things.

Not sure if the dinan springs may be playing a role too.

So, you have had suspension damange repaired, installed rear tires that are smaller in OD than the front, and the car has Dinan springs, all of which results in many combinations of things that could be contributing to your problem. Of one thing however I am reasonably sure. If your handling issues persist with DSC off, then the different tire diameters are not the problem. I drove my car hard this morning with the square 275/35-18 setup. With DSC on, the intevention was definitely more intrusive compared to the OE wheel/tire combination. The difference is not great, but noticeable for sure. With DSC off, the car drives like a charm, very neutral. The PSS tires communicate well, making it easy to maintain balance with the throttle on corner exit. You may have several things going on, but it sure sounds to me like there is a fundamental suspension issue involved.

[Mason3]

Fwiw, i just put PS2's in 255/35 19 and 295/30 19 and have no issues at all. 9 and 10.5 rims respectively. No squirrelly driving, etc.

[LarThaL]

Originally Posted by DirtyJersey

Hi fanatics,

Could a single side wall tire size difference from front to back make an M feel completely uncharacteristic? Especially if the front remained the same and the rears were reduced a size?

Changed my tires on a 2009 e92 M3 with OEM ZCP wheels and I kept the fronts at 245/35/19 (didn’t have 30s) and went with 265/30/19 on the rears….PS2s. I did this after some light suspension work in the front right and back right after the car slide into a curb. The dealer swears everything lined up and aligned dead even and straight.

However, the car feels way off, unstable and even wobbly when quickly shifting its weight from side to side. So much so that the traction control comes on from swinging it back and forth at around 60 (and I don’t mean whipping it….quick and short shifts back and forth). The back end almost feels like it take a fraction of a second to catch up with what everything else is doing….weird…..but I know something is off.

Dealer is blaming the tire size difference, and that the car is compensating for the difference, saying if I go with 30s in the front this would “fix” it. Tho I understand, I have a feeling its more something with the suspension instead.

Any advice, experience, expert opinions? Car seems a bit scary to drive at this point.

My main question to you is why did you change to a 265/30 on the rear? Traction control systems and ABS systems are calibrated with a certain overall tire diameter in mind. You can change tire width, but not the RATIO of the F/R diameter too much without running into problems. Going from a 265/35 to a 265/30 is decreasing the sidewall height by 13mm. This is a big change. You will correct some of the problem by changing to a 245/30 in front,, but your speedmeter will also be off now.

Again....what was your reason for doing this?

I personally think the best tire size on the M3 is 255/35 front and 275/35 rear. You are getting better traction, sidewall height changes by only 3.5mm, the F/R ratio is properly maintained, and you get a more filled out look with a little less fender gap. These sized tires will also fit perfectly on stock BMW wheels.

[bigjae1976]

Originally Posted by DirtyJersey

An update: turning off dsc doesnt really yeild much of a difference. Which is odd if dsc is in fact intervening. Also just yesterday some weird things happpened when i was driving with the car seemingly lurching a couple times while i was steadily driving along. Right after, driving stability lights came on telling me to reduce speed and avoid hard braking. It quickly went out automatically a few mins later.

I thought that even if you turn DSC off, that ABS will still intervene? Is your issue only when you have the brakes applied?

I think the only way to test is to compare to the OEM sizes.

The more threads I see about this, the more I am convinced that you MUST maintain the staggered tire diameters...just like OEM. So square setups may not be so great.

[meyergru]

As to the diameter difference front to rear: For sure there have been problems with Non-M E92s in the past with differences of more than 3%. However, the M3 most surely has a larger allowance for that in DSC and ABS - even considering the normal difference because of the staggered setup.

Proof:

1. Tire wear alone can account for ~4% difference when one pair of tires are worn and one is still O.K. with no problems whatsoever.

2. The only winter setup BMW recommends is 235/40 R18 all around - obviously same diameters don't hurt either.

So: Given the history of the car, I'd guess it's a suspension problem.

[JAJ]

Did you ever find out what the problem is on this?

The difference in tire sizes front to rear is not an issue - the E9x M3 is very tolerant of front-to-rear diameter differences. I had track tires in the same size combo (only in 18" with 245/40 F & 265/35 R) and had no problems at all.

However, you should take a close look at the tires on the car and confirm the exact type on each corner. You said you had PS2's on the rear, but according to Michelin's catalog, Michelin doesn't make a 265/30x19 PS2. There's a Sport Cup and a Super Sport in that size, but not a PS2.

Mixing tire types can make for weird handling.

What makes no sense to me is the idea of a dealer kitting you out with the wrong tires. That's the real mystery.

Originally Posted by DirtyJersey

Hi fanatics,

Could a single side wall tire size difference from front to back make an M feel completely uncharacteristic? Especially if the front remained the same and the rears were reduced a size?

Changed my tires on a 2009 e92 M3 with OEM ZCP wheels and I kept the fronts at 245/35/19 (didn’t have 30s) and went with 265/30/19 on the rears….PS2s. I did this after some light suspension work in the front right and back right after the car slide into a curb. The dealer swears everything lined up and aligned dead even and straight.

However, the car feels way off, unstable and even wobbly when quickly shifting its weight from side to side. So much so that the traction control comes on from swinging it back and forth at around 60 (and I don’t mean whipping it….quick and short shifts back and forth). The back end almost feels like it take a fraction of a second to catch up with what everything else is doing….weird…..but I know something is off.

Dealer is blaming the tire size difference, and that the car is compensating for the difference, saying if I go with 30s in the front this would “fix” it. Tho I understand, I have a feeling its more something with the suspension instead.

Any advice, experience, expert opinions? Car seems a bit scary to drive at this point.