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      12-07-2011, 06:45 PM   #1
LarThaL
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Why did BMW choose 245/265 for the M3?.....

It seems to me that the car just plain needs more grip. Why this tire size? What is the advantage?
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      12-07-2011, 06:54 PM   #2
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I know that lower fuel economy is a reason for not fitting gumballs. in europe, the standards are TOUGH in relation to CO2 emissions.

They probably fitted larger tires and found a diminishing return...-5% in MPG, and +1% in grip. Some enthusiasts would still make that trade, I would bet!
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      12-07-2011, 07:01 PM   #3
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Without speaking to the engineer that specified the tire size, I'd speculate that packaging was a major concern.

Moving beyond the 245/265 tire size really makes it difficult to fit the front tire inside the wheel well without rubbing on the fender liner, as most people with aftermarket wheels know.
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      12-07-2011, 07:05 PM   #4
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Wider wheels actually get BETTER mileage. The wider the tire, given same pressure and type of tire, have much less deformation and thus less friction on the road than a skinny tire at speed. Remember no matter what the width is of the tire, if the PSI is the same, the contact patch touching the ground at any given time is exactly the same area. Its simply a different shape depending on how wide the tire is. Therefore the same amount of "tire material" is producing resistance against the road. However with a wider tire, and thus a wider but skinnier contact patch, less deformation means less friction and wasted energy/heat which means less resistance and better milage.

I know counterintuitive as bicycles often use super skinny tires. So its not milage. I agree thought 285 would have been nice in back and could keep the 245 in front
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      12-07-2011, 10:31 PM   #5
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Quote:
Originally Posted by Ateam View Post
Wider wheels actually get BETTER mileage. The wider the tire, given same pressure and type of tire, have much less deformation and thus less friction on the road than a skinny tire at speed. Remember no matter what the width is of the tire, if the PSI is the same, the contact patch touching the ground at any given time is exactly the same area. Its simply a different shape depending on how wide the tire is. Therefore the same amount of "tire material" is producing resistance against the road. However with a wider tire, and thus a wider but skinnier contact patch, less deformation means less friction and wasted energy/heat which means less resistance and better milage.

I know counterintuitive as bicycles often use super skinny tires. So its not milage. I agree thought 285 would have been nice in back and could keep the 245 in front
Not entirely true.
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      12-07-2011, 11:18 PM   #6
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Performance, handling, fuel economy, cost, availability, logistics, available space, safety...

Many factors to consider...
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      12-12-2011, 09:20 AM   #7
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Even if it came with 265/285 people would be asking why it didn't come with 285/305.

The stock tire size is plenty for the street.
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      12-12-2011, 09:25 AM   #8
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Quote:
Originally Posted by Muffnbluff View Post
Even if it came with 265/285 people would be asking why it didn't come with 285/305.

The stock tire size is plenty for the street.
This.

I think the car has plenty of grip, for street driving. More than 99% of cars on the road, I imagine.
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      12-12-2011, 11:07 AM   #9
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i noticed a noticable difference when i went to 255/35 and 275/35
i think that is the perfect combo
any more (unless you are supercharged) is just for bragging rights
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      12-13-2011, 01:47 PM   #10
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Quote:
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285 would have been nice in back and could keep the 245 in front
245 front with 285 rear would understeer in a front engine car like the M3. The car is already set up for some understeer for stability, but they want to keep it fairly neutral so that it is fun to drive hard. To keep the handling balance they wanted, they probably didn't want to have too much stagger.
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      12-13-2011, 01:54 PM   #11
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I daily with 275/35/18 and 285/35/18

it's great fun
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      12-13-2011, 02:28 PM   #12
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You have to remember that the EU has a requirement for snow chains to be compatible with the OEM tire sizes...or something. So BMW cannot have the tires flush with the fenders.

As a rule of thumb, I've been told that a 12mm spacer will push the tire to about even with the fender.
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      12-13-2011, 02:37 PM   #13
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Quote:
Originally Posted by Ateam View Post
Wider wheels actually get BETTER mileage. The wider the tire, given same pressure and type of tire, have much less deformation and thus less friction on the road than a skinny tire at speed. Remember no matter what the width is of the tire, if the PSI is the same, the contact patch touching the ground at any given time is exactly the same area. Its simply a different shape depending on how wide the tire is. Therefore the same amount of "tire material" is producing resistance against the road. However with a wider tire, and thus a wider but skinnier contact patch, less deformation means less friction and wasted energy/heat which means less resistance and better milage.

I know counterintuitive as bicycles often use super skinny tires. So its not milage. I agree thought 285 would have been nice in back and could keep the 245 in front
Couple of things:
Aero my friend, aero..... There are some good studies on the effects of wider tires on Cd.
There are also lots of presumption built into your original statement. For example, does the width of a tire have a disproportionate effect on a vehicle that has toe? (scrub radius, etc)

Sometimes the truth is a few layers deep!
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