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      10-10-2017, 10:41 PM   #1
jackliu0527
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Tire Setup

I want to ditch my crappy oem dunlop rft tires soon on my xdrive, and was doing some research and found something interesting

20inch oem tire size is 245/35/20FR and 275/30/20RR, according to factory setup the rear tire has 1.1% less diameter than the front same goes for rolling circumference, which is weird i thought BMW dont recommend >1% difference?

so if i want wider tires do i got with 255/35/20FR and 285/30/20RR? this setup also have 1.1% difference between front and rear

but with 245/35/20FR and 285/30/20RR the diameter is exactly the same between front and rear tires

or 40FR and 35RR aspect ratio? i dont think there is enough clearance for it

has anyone tried any of these setups?

Last edited by jackliu0527; 10-10-2017 at 11:26 PM..
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      10-10-2017, 11:05 PM   #2
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20inch oem tire size is 245/35/20FR and 275/35/20RR,

Stock is 245/35/20 front, 275/30/20 rear for the 640 & 650.

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      10-10-2017, 11:27 PM   #3
jackliu0527
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sry typo i meant to say 30, anyhow you got any inputs regarding this issue?

Last edited by jackliu0527; 10-10-2017 at 11:35 PM..
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      10-11-2017, 08:49 AM   #4
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Originally Posted by jackliu0527 View Post
sry typo i meant to say 30, anyhow you got any inputs regarding this issue?
If you want a wider staggered setup then you want a 255/35/20 front and 295/30/20 rear, which are the exact same diameter. BUT - the 295's might look funny on the stock staggered 9" rear wheel. Never tried it.
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      01-29-2018, 04:52 AM   #5
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OP I'm in the same boat right now

What setup did you end up with?

I read here and on bimmerfest that other owners are installing tires with larger side wall such as 245 or 255/40/20F and 275 or 285/35/20F non-RFT which significantly improved the ride quality. Also read that 255/40/20 may require spacer depending on the offset.

I want go one step larger side wall and wider in the back but OEM wheels are thin and the setup might be out of spec.
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      02-02-2018, 10:03 AM   #6
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I'm bumping an old thread and would like some help I'm thinking of going with larger side wall non-run flats on my 650i not m sport with stock springs.

Is it possible to fit 245 or 255/40/20 front and 275 or 285/35/20 rears on stock rims to fill the wheel well? Do I need a spacer upfront to avoid rubbing?
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      02-02-2018, 10:27 AM   #7
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Originally Posted by MBMW View Post
I'm bumping an old thread and would like some help I'm thinking of going with larger side wall non-run flats on my 650i not m sport with stock springs.

Is it possible to fit 245 or 255/40/20 front and 275 or 285/35/20 rears on stock rims to fill the wheel well? Do I need a spacer upfront to avoid rubbing?
you should be fine on a 255/40/20 and a 295/35/20, with no spacers. They are an inch taller than the 255/35 and 295/30 I currently run, and are only off in diameter by a tenth of an inch, which is perfectly acceptable. they are only marginally, wider, and I have plenty of room and never, ever rub with my current set up.

Note that I use those sizes on M5 343M wheels, so the offsets are different.
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Last edited by upstate650; 03-12-2018 at 12:30 PM..
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      02-02-2018, 10:30 AM   #8
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Quote:
Originally Posted by upstate650 View Post
Quote:
Originally Posted by MBMW View Post
I'm bumping an old thread and would like some help I'm thinking of going with larger side wall non-run flats on my 650i not m sport with stock springs.

Is it possible to fit 245 or 255/40/20 front and 275 or 285/35/20 rears on stock rims to fill the wheel well? Do I need a spacer upfront to avoid rubbing?
you should be fine on a 255/40/20 and a 295/30/20, with no spacers. They are an inch taller than the 255/35 and 295/30 I currently run, and are only off in diameter by a tenth of an inch, which is perfectly acceptable. they are only marginally, wider, and I have plenty of room and never, ever rub with my current set up.
Thanks for the feedback

Are you using wider wheels?
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      02-02-2018, 10:35 AM   #9
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Thanks for the feedback

Are you using wider wheels?
I edited my post to add that I am using those tires on M5 343M wheels, so yes.
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      03-10-2018, 06:36 AM   #10
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Reviving an old thread, but curious on what you went with MBMW. I need some new rubber on 640d m-sport and was looking at 275/35/20 or 285/30/20 anyone any experience with these sizes? Non xdrive so not bothered about the difference front to back. Only looking to do the rears as loads of tread on the front.
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      03-11-2018, 05:27 AM   #11
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Right looking at diameter of tyres, I'm going in the direction of 285/35/20 rear and 245/40/20 on the front. Rear will be 5mm higher in diameter but as rears wear wicket than fronts it should work out well. Plus I'm rear wheel drive so didn't see much issues. This adds about 30mm extra to the diameter of the wheel which should fill the wheel well a bit better. Only concern I have is that it rubs but, suspect this increase should be fine if others are running 21 inch wheels and others with M5 wheels aren't having problems with wider stance. This will be on standard staggered 373 rims which I accept is a different offset to 343 rims but expect it will be ok. The other benefit is that at these sizes I can run Michelin PS4'S.

Looking at doing the fronts at the same time now as may as well get the whole car on the same tyre and go full non rft.

Anybody any experience of increasing tyre sizes to these? I'm looking to add a bit of extra sidewall to give a bit more protection to the rims and also fill the wheel well a bit better.
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      03-12-2018, 12:27 PM   #12
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Im going to jump in on this since its been revived...

Trying to make a decision on new tire and Im really interested as to why the more common upgrade I see on the forums is to 255/35/20 285/30/20 when 245/30/20 285/30/20 is closer in rolling diameter?
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      03-12-2018, 02:47 PM   #13
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255/285(35/30) keeps the factory ratio of 245/275(35/30), however with the factory setup, front tire is slightly larger than the rear, as to why, its beyond me, maybe someone else here would know, but either is some engineering I do not understand, or that BMW just got a better deal on tires that ratio.

However with the 245/285(35/30) or 255/295(30/35) set up, the front tire and the rear tire are exactly the same diameter, which theoretically is a better setup, however I am no engineer nor a experience mechanic so I cant really comment on it, I am pretty torn myself between the choices
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      03-12-2018, 03:53 PM   #14
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Just a data point... the B6 GC uses the same overall diameter front to back.
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      03-15-2018, 08:19 PM   #15
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Quote:
Originally Posted by jackliu0527 View Post
255/285(35/30) keeps the factory ratio of 245/275(35/30), however with the factory setup, front tire is slightly larger than the rear, as to why, its beyond me, maybe someone else here would know, but either is some engineering I do not understand, or that BMW just got a better deal on tires that ratio.

However with the 245/285(35/30) or 255/295(30/35) set up, the front tire and the rear tire are exactly the same diameter, which theoretically is a better setup, however I am no engineer nor a experience mechanic so I cant really comment on it, I am pretty torn myself between the choices
Thanks for that info. That makes sense exactly as you say it. So Im good to go either way. 255/35/20 is actually a couple of bucks cheaper than the 245/35 for the tire Im looking at.
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      03-15-2018, 10:12 PM   #16
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This is based on my personal experience and only my opinion.

I’ve noticed on a stock 20x8.5 wheel a 255/35 is a little big.
And by big I mean...if you get a tire with a soft sidewall. You’ll notice a little bit of flex on turn-ins. But this all comes down to tire brand and the compound used.

It also comes down to how you drive your cars and a few other factors (but that’s a discussion for another day)

I find that a 245 is the sweet spot. It still gives a smooth and comfortable ride. But when you jump on it. You can take a corner with confidence.
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      03-16-2018, 08:55 AM   #17
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Originally Posted by Nice95gle View Post
This is based on my personal experience and only my opinion.

I’ve noticed on a stock 20x8.5 wheel a 255/35 is a little big.
And by big I mean...if you get a tire with a soft sidewall. You’ll notice a little bit of flex on turn-ins. But this all comes down to tire brand and the compound used.

It also comes down to how you drive your cars and a few other factors (but that’s a discussion for another day)

I find that a 245 is the sweet spot. It still gives a smooth and comfortable ride. But when you jump on it. You can take a corner with confidence.
I don't find this to be true at all. I run a 255/35/20 winter tire on 8.5" wheel on the front for my winter set up and it doesn't bulge at all. The rear of my winter setup is the same size tire on the 9" 373 and it has no rim coverage at all.
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      03-16-2018, 09:01 AM   #18
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Quote:
Originally Posted by elvisisdog View Post
Right looking at diameter of tyres, I'm going in the direction of 285/35/20 rear and 245/40/20 on the front. Rear will be 5mm higher in diameter but as rears wear wicket than fronts it should work out well. Plus I'm rear wheel drive so didn't see much issues. This adds about 30mm extra to the diameter of the wheel which should fill the wheel well a bit better. Only concern I have is that it rubs but, suspect this increase should be fine if others are running 21 inch wheels and others with M5 wheels aren't having problems with wider stance. This will be on standard staggered 373 rims which I accept is a different offset to 343 rims but expect it will be ok. The other benefit is that at these sizes I can run Michelin PS4'S.

Looking at doing the fronts at the same time now as may as well get the whole car on the same tyre and go full non rft.

Anybody any experience of increasing tyre sizes to these? I'm looking to add a bit of extra sidewall to give a bit more protection to the rims and also fill the wheel well a bit better.
since you are RWD the height difference isnt an issue - the question is whether they will rub due to height difference. Let us know how it works out!
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      03-16-2018, 12:27 PM   #19
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Hey upstate 650, you seem pretty educated on the tires, I was wondering if you can help me decide

I am running factory OEM wheel (373) at 8.5FR and 9RR, I want to swap out my crappy dunlops for pilot sport 4s at 255/285 or 255/295, do you have any experience or know anyone running those setups? I am worried that 255 will bulge on the 8.5 fronts, and 285 or 298 bulging on the 9 rear, and if those fitment does work, what are the draw backs if there are any, performance, ride quality, etc?

advice would be greatly appreciated
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      03-16-2018, 12:33 PM   #20
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Quote:
Originally Posted by jackliu0527 View Post
Hey upstate 650, you seem pretty educated on the tires, I was wondering if you can help me decide

I am running factory OEM wheel (373) at 8.5FR and 9RR, I want to swap out my crappy dunlops for pilot sport 4s at 255/285 or 255/295, do you have any experience or know anyone running those setups? I am worried that 255 will bulge on the 8.5 fronts, and 285 or 298 bulging on the 9 rear, and if those fitment does work, what are the draw backs if there are any, performance, ride quality, etc?

advice would be greatly appreciated
I've never seen anyone run that set up on 373 wheels. The 255/35 on the 8.5" wheel isn't an issue at all. The 295/30 on a 9" wheel is going to have quite a muffin top. It looks beefy on a 10" wheel.

First question is do you have xdrive - because if you do, you definitely should NOT be running a 255/35/20 285/30/20 setup.
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      03-16-2018, 03:39 PM   #21
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Quote:
Originally Posted by upstate650 View Post
I've never seen anyone run that set up on 373 wheels. The 255/35 on the 8.5" wheel isn't an issue at all. The 295/30 on a 9" wheel is going to have quite a muffin top. It looks beefy on a 10" wheel.

First question is do you have xdrive - because if you do, you definitely should NOT be running a 255/35/20 285/30/20 setup.
I have X-drive yes, why wouldent I run 255/285? its the same factory ratio of 245/275, i know the fronts are slightly larger, but factory does run that set up

So if 295 no good on 9" how about 285? maybe I can run 245/285 which is same diameter
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      03-16-2018, 04:10 PM   #22
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Quote:
Originally Posted by jackliu0527 View Post
I have X-drive yes, why wouldent I run 255/285? its the same factory ratio of 245/275, i know the fronts are slightly larger, but factory does run that set up

So if 295 no good on 9" how about 285? maybe I can run 245/285 which is same diameter
A 295/30/20 tire is 27" tall. So is a 255/35/20, which is why they are a perfect match.

A 285/30/20 is only 26.7" tall, so you are starting out with a difference of just over 1% when the tires are brand new.

Tread depth is 10mm. At half wear on the 285/30, the tire will only be 26.3-26.4" tall. If the front are wearing half as fast at the rears, the front tire is now 26.8-26.9" tall. The difference is around half an inch, which is approximately 2%.

The generally accepted limits in tire height difference for the x drive system is 1%. But this applies at every point during the life cycle of the tires. So if you start out with a 1% difference, you need to know what will happen to that percentage over time. On the 6 series, the height difference will increase over time because the rears wear faster than the front, and on the setup you are using the rear is already the smaller tire.

I've run through 3 sets of rears and one set of fronts on my car with 255/35 front and 295/30 rear with no issues.

Several people have tried running 255/35 and 285/30 and have reported issues. Its your car, though, so do what you want.

the 245/35/20 and 285/30/20 are only off by .1 inch and are probably the best solution if you want to use the 373 wheels.

I can't explain why BMW sells the 245/275 set up. They are violating their own recommendations. Unless that set up doesn't come on x drive vehicles? I honestly don't know if it is only on RWD vehicles or both RWD and xdrive.
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