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Discussion Starter · #1 ·
I was wondering why bmw has a tendency to stuff larger size width tires onto somewhat small wheels for that size.

For example my car and all 07s I believe had 245 tires on an 8 inch wheel. The 550 and now the 535 sport has 245s on 8 inch wheels in front and 275 on 9 inch wheels in the rear.

245s on an 8 inch wheel is usually not thought of as the right fit and same with 275s on a 9 inch wheel.

For those wheels the more appropriate size is a 225 tire on an 8 inch wheel and a 255 on a 9 inch wheel.

At the very most a 235 on an 8 inch wheel and 265 on a 9 inch.

Why does bmw do this? Why not put 9inch wheels up front and 10 inch rears which are the right sizes for the 245/ 275 combo.

If you look at tire rack you can see for example by putting a 245 tire on an 8 inch wheel-you have pretty much no more contact patch then a 235 tire on that same 8 inch wheel since the 245 ends up balooning the sides out somewhat.

Any thoughts?
 

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You seem to have a strong opinion on this, but haven't supported your opinion with any facts.

There have been several members in the past like this--are you familiar with any of them:
Driftin = jacktown = Zed2Zee = sleepyca31 (the 31 at the end of your name caught my attention).

My 545i has 245/40 on 8" on front, and 275/35 on 9" on rear.

My '03 E55 had 245/40 on 8" on front, and 265/35 on 9" on rear.

Neither car's tires suffer from the "ballooning" you refer to, and to my eye fit the wheels fine.

So AMG and BMW would disagree with your opinion. ;) What exactly are you basing it on?
 

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Discussion Starter · #3 ·
This is actually the first time I have found a bmw board or internet board of any type so not sure what the reference to the list of names you listed other than someone else happened to have a 31 in their name?

I do not feel strongly, I was just curious. If you look online or tirerack.com you see the specs of a tire listed and the wheel range in which that tire fits on. It also lists the wheel size that a certain tire size is measured with. For the 245s it is an 8.5 and the 275s its a 9.5. The reason I ask and you are correct that they fit fine, however a 275 tire on a 9 inch wheel is not as wide as that same tire on a 10 inch wheel for example. It is .2 inches for each half size up in wheel you go. So the 275s on a 10 inch wheel would be 0.4 inches wider with the same tire. That is almost half an inch which is a lot. So I am saying if bmw wants 275s on then why not make the most of them by marrying them with a 10 inch wheel to get the most width out of the tire possible. If not then why not use a 265 tire since that will be the same width on a 9 inch wheel as a 275 tire would.

You can see this at tire rack. Go to any tire and pull up the specs, then look at Spec width which is the width of the tire when mounted on a wheel. You will see a 265 tire is as wide as a 275 when you are on 9 inch wheels. You just have to play around with the .2 correction factor which you can read about at tirerack as well.
 

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You can see this at tire rack. Go to any tire and pull up the specs, then look at Spec width which is the width of the tire when mounted on a wheel. You will see a 265 tire is as wide as a 275 when you are on 9 inch wheels. You just have to play around with the .2 correction factor which you can read about at tirerack as well.
Tires can fit on a range of wheel sizes, usually between 75% to 100% of the tire width. Using a narrower tire will help protect the wheel, and I suspect the wider wheels will likely have fitment issues. The ride is also a bit softer on narrower wheels.

As for performance, several autocross sites I visited indicated that using the widest tire you can fit on a given wheel width provided optimum performance, despite the fact that the sidewalls "balooned."
 
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