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      01-30-2009, 06:49 PM   #1
V8 POWER
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Why did BMW NOT put larger tires on the M3?

Every time I take my M3 out I am still amazed about the power at the rear wheels.

And for car enthusiasts that is coming from an 2004 Porsche GT3.

Why did BMW not make the M3 with 305's at the rear? It appears that 305's will fit without out any modifications to the wheel well. I can only imagine how much faster the car would accelerate with more rubber and traction in the back.

Any ideas why the put 265's and not something bigger in the rear?

Some ideas that I came up with:
  • too expensive
  • smaller rolling mass
  • less resistance
  • ride quality
  • creates too much oversteer
  • differential could not take it
  • ?
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      01-30-2009, 07:01 PM   #2
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The biggest difference is that the M3 rears don't have to hold over 60% of its weight in a turn. The M has near 50/50 balance and is a fairly neutral car. I could see a 'little' more rear tire to help put power down out of the turns but only with a comparable front tire increase to not mess up the balance with increased understeer. More is not always better. You'd need enough rim width (larger and heavier) to actually maintain a good contact patch and you want to be able keep enough heat in the tire to maintain optimum stick.
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      01-30-2009, 07:27 PM   #3
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Quote:
Originally Posted by Ronin13 View Post
....and you want to be able keep enough heat in the tire to maintain optimum stick.
I like this point! Never thought of that. 911 has all that weight to press onto the rear tires.
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      01-30-2009, 08:43 PM   #4
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Quote:
Originally Posted by V8 POWER View Post
Why did BMW not make the M3 with 305's at the rear? It appears that 305's will fit without out any modifications to the wheel well. I can only imagine how much faster the car would accelerate with more rubber and traction in the back.
You are touching there a single point which is straight line acceleration and in that point you are right. The problem is that the car has also to turn and the wider the wheel the more tradeoffs you have to do with the suspension. A 305 in the rear will require 275-285 in the front (to avoid massive understeer) which will require reinforcing of the suspension to adjust for the higher adhesion which in turn will need a change in geometry to account for the higher body roll and I could go on and on.... so yes, in the end tire size is an engineering compromise which takes into account many variables.
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      01-30-2009, 09:51 PM   #5
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i think 305 is overkill
but why not 265 in the front and 285 in the back?
i think the 265 is a joke for 414hp
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      01-30-2009, 10:52 PM   #6
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What is the optimum tire size for this car, I'm changing tires and I would like to have more rubber, but I don't want to compromise handling, so what would be biggest tire combo, front and rear the car can handle, without compromising anything, I have the 19"OEM Rims,
thanks in advance
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      01-30-2009, 10:52 PM   #7
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^ That would seem to be the best compromise 265/285, if the wheel size is increased from OEM.
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      01-31-2009, 02:13 AM   #8
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Quote:
Originally Posted by kmarei View Post
i think 305 is overkill
but why not 265 in the front and 285 in the back?
i think the 265 is a joke for 414hp
I would have to agree. Wheelspin is ridiculous without DSC on.
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      01-31-2009, 05:13 AM   #9
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I think 255 front, 285 rear would be ideal.
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      01-31-2009, 08:40 AM   #10
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Quote:
Originally Posted by MrHarris View Post
I think 255 front, 285 rear would be ideal.
the reason i said 265 and 285 is to maintain the stock balance of the car
you don't want to mess with that or the car oversteers too much or understeers
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      01-31-2009, 08:46 AM   #11
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Quote:
Originally Posted by CodeRed View Post
^ That would seem to be the best compromise 265/285, if the wheel size is increased from OEM.
well the rear 9.5" wheel can take the 285 tire
but the front 8.5" wheel can't take the 265 rubber
i know of one person who bought an extra set of OEM wheels and used all 4 9.5" wheels for summer and the 4 8.5" wheels for winter
that's a good idea

not a fan of aftermarket wheels, or using spacers etc
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      02-02-2009, 01:23 AM   #12
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Quote:
Originally Posted by vm View Post
A 305 in the rear will require 275-285 in the front (to avoid massive understeer) which will require reinforcing of the suspension to adjust for the higher adhesion which in turn will need a change in geometry to account for the higher body roll and I could go on and on....
I agree that the tires, wheel and suspension are a system, designed to work in concert. However you are wrong that a 275 front width will require "reinforcing the suspension" (whatever that means...). The car will take wider and stickier tires with just fine with absolutely no suspension modifications. I have not done it myself but I'm pretty sure a couple folks here run 285 square set ups with track rubber with no problems. Even if I did not have empirical evidence the logic of engineering safety factors dictates this simply could not be the case.
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      02-02-2009, 01:42 AM   #13
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Quote:
Originally Posted by kmarei View Post
i know of one person who bought an extra set of OEM wheels and used all 4 9.5" wheels for summer and the 4 8.5" wheels for winter
that's a good idea
So would 265 with 18x9.5 rears fit in the front without poke or any fitment issues?
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      02-02-2009, 01:51 AM   #14
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BMW picks their tire sizes to deal with all weather conditions including heavy rain and standing water. For a daily driver they're perfect. For track work, you can do better.

The M3 will take as much as a 275 up front and 305 at the rear - the trick is finding them in a tire type that meets your needs.

There's no doubt the wheel wells were built with bigger tires and rims in mind - the larger rims and tires fit without any drama provided you get the wheel offsets right.
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      02-02-2009, 12:03 PM   #15
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Quote:
Originally Posted by swamp2 View Post
Even if I did not have empirical evidence the logic of engineering safety factors dictates this simply could not be the case.
Swamp - as someone who has suffered shock tower failure on a modded road car I can say it's not always as simple as that. Yes it ran aftermarket shocks but only lightly re-valved Koni yellows.
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      02-02-2009, 05:32 PM   #16
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So you could go 285/35/19 on the OEMs in the rear and 265/35/19 on the front without problem or issue?
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      02-02-2009, 09:32 PM   #17
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Quote:
Originally Posted by swamp2 View Post
I agree that the tires, wheel and suspension are a system, designed to work in concert. However you are wrong that a 275 front width will require "reinforcing the suspension" (whatever that means...). The car will take wider and stickier tires with just fine with absolutely no suspension modifications. I have not done it myself but I'm pretty sure a couple folks here run 285 square set ups with track rubber with no problems. Even if I did not have empirical evidence the logic of engineering safety factors dictates this simply could not be the case.
The one that's wrong is you. Reinforcing the suspension means exactly that; ie bigger ball joints and suspension elements. Now we are talking about different things here. What you say is that any particular (and hopefully knowledgeable) person can mod the car and the car will not self destruct and this is fine with me BUT this will result in shorter component life. There is no way around that. So any manufacturer will have an expected life in each component and that's what they use to size them. So if the BMW factory decides to use these larger tire sizes they will need to upgrade the suspension/chassis to handle the larger loads at the same expected life as before the upgrade.
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      02-03-2009, 01:36 AM   #18
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...bigger ball joints and suspension elements...this will result in shorter component life.
The factory used larger and stronger parts on the M3 than they did on the regular 3-series. That said, you're right - the harder you drive and the more grip you get (bigger tires or stickier tires) the more stress and the shorter the life of the components. Unless you run the stock tires and drive moderately you'll get less life than the factory norm. I think we all get that.
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      02-03-2009, 01:46 AM   #19
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Originally Posted by Ramphaus View Post
So you could go 285/35/19 on the OEMs in the rear and 265/35/19 on the front without problem or issue?
Check this thread: http://www.m3post.com/forums/showthr...ighlight=corsa

He used 265/30's and 285/30's and they worked. 35's might be too tall to fit properly though.
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      02-04-2009, 10:12 PM   #20
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Quote:
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Swamp - as someone who has suffered shock tower failure on a modded road car I can say it's not always as simple as that. Yes it ran aftermarket shocks but only lightly re-valved Koni yellows.
Yes, been there myself with various chassis and suspension failures in my E36 M3. Sure suspension mods, springs and damping along with possibly very sticky race type rubber and you can get substantially more loads in the suspension system. As well I imagine you were driving the said car really hard with track work likely. This is not what I was referring to. All of these things can certainly combine to produce high enough loads to cause premature failures in chassis or suspension components. But non track tires, 10 or 20 mm wider? Nope, you would have imperceptibly more loads in the suspension system. The biggest factor is the fact that modded cars get driven much harder.

Quote:
Originally Posted by vm View Post
The one that's wrong is you. Reinforcing the suspension means exactly that; ie bigger ball joints and suspension elements. Now we are talking about different things here. What you say is that any particular (and hopefully knowledgeable) person can mod the car and the car will not self destruct and this is fine with me BUT this will result in shorter component life. There is no way around that. So any manufacturer will have an expected life in each component and that's what they use to size them. So if the BMW factory decides to use these larger tire sizes they will need to upgrade the suspension/chassis to handle the larger loads at the same expected life as before the upgrade.
Still disagree, see above. Apples to apples, nothing else changing but 10-20 mm wider for a tire absolutely will not "require" (your exact wording, "REQUIRE"!) such suspension modifications. It would not be "required" neither at the consumer, do it yourself, level nor at the design level by the OEM. The loads will be higher but probably imperceptibly so. The safety factors and lifetime of such components will more than offset the increased loads. Sure in principal more load = more stress = shorter life, but this is not unconditionally true in all cases. I'd be willing to bet a whole host of other factors would create more "noise" in any real world test designed to observe a change in lifetime of any suspension components based on 10-20mm wider tires.

By the way there is way, way more that goes into sizing any given component other than just desired lifetime.
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      07-31-2009, 08:43 PM   #21
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i'm going to lean towards bmw's r&d on this one. if there was a much better solution, they probably would've gone for it. on a $65k car, if they added a few dollars for a much better tire/size, they would've done it. this car handles amazingly well, and mine seems to get great traction on take off. i think it's fine with stock sizes
just my $.02
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      08-01-2009, 04:26 AM   #22
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i'm going to lean towards bmw's r&d on this one. if there was a much better solution, they probably would've gone for it. on a $65k car, if they added a few dollars for a much better tire/size, they would've done it. this car handles amazingly well, and mine seems to get great traction on take off. i think it's fine with stock sizes
just my $.02
+1
If you want more grip then fit Cup+ tyres...if its just a dick measuring contest then fit the biggest rubber you can, regardless of how its going to mess up the balance.
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