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[E92_328i_Boston]

My apologies in advance if this has been covered previously. I did search, but couldn't seem to find the exact answer.

What are the stock tire weights of my 225/40 and 255/35 Bridgestone run-flats on my 2008 328i coupe?

I would like to know because I am trying to determine the specific weight difference when I switch to non-run-flats next year (probably Pilot Sport PS2s from what I've seen on the forums).

Previous experience has taught me that lessening the unsprung weight by a few pounds on each corner has dramatic effects. I can remember how much more agile and "quick" my 2001 325Ci felt with 225/45s all around as opposed to 235/45s (which I went with once just out of curiosity). The mpg was definitely affected too. And that was just a small difference on each corner (a couple of pounds at most).

In summary, I am wondering how much weight will be saved and what kind of an effect have people seen with regards to mpg, handling, acceleration, etc.

Thank you in advance for your responses.

-A

[stressdoc]

You can check tire weights at TireRack.
I weighed mine at 25 & 27 lbs at 1k miles.

Michelin PS2s are 21 & 24 lbs. (light)

Extreme performance tires tend to be in the 24-27 lbs range.

[E92_328i_Boston]

Indeed, mea cupla.

It looks like the stock B run-flats are 25 front and 26 rear. The PS2s are 22 front and 25 rear.

Can someone comment on whether or not they've seen increased responsiveness and better mpg after losing a few pounds in each corner?

-A

[jopa489]

I think it's insignificant on a daily driver. When dealing with a track car and looking to squeeze every bit of power while loosing every extra ounce of weight, you might notice a difference. For a car that is not exactly lightweight such as the E9x, saving 15lbs isn't going to matter much.

[David9962000]

Any weight not supported by the suspension in called unsprung weight ( Wheels, brakes, tires...) and is multiplied by 4. You save 1LBS = 4LBS.

http://en.wikipedia.org/wiki/Unsprung_mass

[MassBimmer]

Originally Posted by David9962000

Any weight not supported by the suspension in called unsprung weight ( Wheels, brakes, tires...) and is multiplied by 4. You save 1LBS = 4LBS.

http://en.wikipedia.org/wiki/Unsprung_mass

This is actually not entirely true...in general, every 1 pound of unsprung weight roughly equals 10 lbs of sprung weight. So if you save 5 pounds per corner, that's 20 pounds of unsprung weight which equals around 200 pounds of sprung weight. Lighter weight wheels are one of the best performance upgrades you can do to a N/A car

[perrymaxima]

Originally Posted by MassBimmer

This is actually not entirely true...in general, every 1 pound of unsprung weight roughly equals 10 lbs of sprung weight. So if you save 5 pounds per corner, that's 20 pounds of unsprung weight which equals around 200 pounds of sprung weight. Lighter weight wheels are one of the best performance upgrades you can do to a N/A car

+1 Don't understand why people buy 18"& 19" wheels that weigh more or equal to our stock setup it's your chance to save a lot of unsprung weight which helps us NA guys with gas mileage and responsiveness. Also keep in mind the track of the car wider wheels increase understeer which is just as bad as heavy wheels.