18"wheels=slow m3

[m3f_bmw4life13_0098c1d2b1]

I drove my friend's '99 m3 convert with dinan everything (chip, cai, suspension, etc) and it felt much slower than my stock m3. :eek2: The only explanation is that he's running 18" BBS wheels. After driving his car I'm definitely sticking with 17" wheels.

[m3f_iNcUbUs_21_0bcd67a730]

Depending on which BBS wheels he's running, they may even be lighter than stock 17's. With those mods the car shouldn't feel slow with 18's. :hmm:

[m3f_PurpleM3Pursuit]

ya gotta remember though.. even if the rims are lighter.. most of the weight is probably further from the hub.. making it tougher to turn the tire.. therefore making it feel slower.. i wanna get some 17's fo sho.. buti just gotta find some that i can afford.. or make more money :P

[m3f_Sirius_880bd69485]

I wouldn't mind downsizing my rims, but I am on the same boat Purp is.

[m3f_astan100_7ef66fbe89]

Your car may also be faster from the factory. There are deviances in engines.

[m3f_bmw4life13_0098c1d2b1]

I'm seriously thinking about just keeping my 17" hamann hm3s now. IMO there aren't many other 17" wheels that look nicer on an e36 m3.

[m3f_Ty Vil_fe6451789c]

The convert is the big factor you're forgetting. It's several hundred pounds heavier.

[m3f_///M3 FX_c539798270]

So you gusy think 17's are the way to go ?

[m3f_kchildre]

So you gusy think 17's are the way to go ?



Absolutely, unless (there is always an unless) you are needing to install a big brake kit and require the clearance for the kit. I've been doing three years of driving schools and unless you are Seriously racing (SCCA / BMW Club Racing Modified or Prepared Class) the stock brakes in these cars are phenominal.



My wheel recommendation (and the ones I bought for my car) are BBS RK 17x8 running a balanced 235/40 tire all around (16 pounds per wheel). Plus the wheels are lighter (than the same wheel in 18s), the wheels are cheaper (than the same wheel in 18s) the tires are cheaper than 18s also.

[m3f_J///MR]

What kind of tires do you like for street/track? I'm running a similar setup (17x8 lightweight wheels w/ 235's), but I'm not satisfied w/ the grip of my cheapo Kumho's. I was planning to get 245's next time...



Absolutely, unless (there is always an unless) you are needing to install a big brake kit and require the clearance for the kit. I've been doing three years of driving schools and unless you are Seriously racing (SCCA / BMW Club Racing Modified or Prepared Class) the stock brakes in these cars are phenominal.



My wheel recommendation (and the ones I bought for my car) are BBS RK 17x8 running a balanced 235/40 tire all around (16 pounds per wheel). Plus the wheels are lighter (than the same wheel in 18s), the wheels are cheaper (than the same wheel in 18s) the tires are cheaper than 18s also.

[m3f_astan100_7ef66fbe89]

I think both the cars are verts...right?

[m3f_Ty Vil_fe6451789c]

i Don't think the wheels are the factor here.

[m3f_iransbest]

My car slowed down when I went to 18's

[m3f_bmw4life13_0098c1d2b1]

I think both the cars are verts...right?

yes both cars are '99 verts. The only differences are the wheels and Dinan upgrades.

[m3f_The Fly_6a68e922d2]

You will get less acceleration with 18's, though it will be less noticeable as you get rolling to higher speeds and the acceleration diminishes with increased drag, etc. Power can be expressed as the difference in kinetic energy in a given period of time. Kinetic energy for a translational (non-rotating) mass is .5*m*v^2, where m is the mass and v is the velocity. Kinetic energy for a rotational mass is the wheels translational KE (above) + rotational KE, which is equal to .5*M*omega^2, where omega is the angular velocity (rpms) of the wheel, and M is the moment of inertia of the wheel. The moment of inertia is .5*m*r^2, where r is the distance of the mass from the axis. Because more weight is further away from the center and there is that squared term, it does make a difference.



If we assume the wheel to be of uniform mass thru the cross section, the above eventually reduces to .75*m*v^2, which means that 10 lbs of rotational mass for a given wheel diameter has the same effect as 15 lbs placed in the car. This is an example and does not yet include the effect of having the weight further from the wheel hub as with an 18".



If someone gets me some wheel weights and wheel cross sections, I could maybe figure better numbers for the actual effect.



The Fly







QUOTE=bmw4life13]yes both cars are '99 verts. The only differences are the wheels and Dinan upgrades.[/QUOTE]