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View Full Version : Recommended Tire Size for 21'' Style 128 Rim?


AngelE66
06-20-2012, 03:47 PM
Hey guys I am in the process of getting a set of 128's in 21'' for my 745Li and need help with tire size as I have no knowledge of tires and rims.

The Rim size are

9" x 21" ET: 22 Front
10" x 21" ET: 32 Rear


I was told to get 245/35 R21 for the front tire and 285/30 R21 for the rear. Would that be correct? I am also putting on the H&R Sports springs at the same time if that makes any difference.

Any help would be appreciated.

wjjklj
06-20-2012, 04:45 PM
That would be the recommended size although I run 255/30/21 up front and 295/25/21 in the rear with no problems.

csmeance
06-20-2012, 09:25 PM
Hey guys I am in the process of getting a set of 128's in 21'' for my 745Li and need help with tire size as I have no knowledge of tires and rims.

The Rim size are

9" x 21" ET: 22 Front
10" x 21" ET: 32 Rear


I was told to get 245/35 R21 for the front tire and 285/30 R21 for the rear. Would that be correct? I am also putting on the H&R Sports springs at the same time if that makes any difference.

Any help would be appreciated.


I would suggest at a MINIMUM 245/35/21 for the front and 285/30/21 for the rears!

However you can go up in WIDTH (first 3 digits) without an issue. 255/35/21 is recommended because it'll give a little better curb rash protection, same with the rears, 295/30/21 will do the same.

AngelE66
06-21-2012, 12:40 PM
I would suggest at a MINIMUM 245/35/21 for the front and 285/30/21 for the rears!

However you can go up in WIDTH (first 3 digits) without an issue. 255/35/21 is recommended because it'll give a little better curb rash protection, same with the rears, 295/30/21 will do the same.



I live in NYC , I don't want to go too low on the tires especially on 21'' rims...

Which set up is more "meatier" and acceptable? 245/35/21 & 285/30/21 OR 255/35/21F & 295/30/21R OR 255/30/21 front & 295/25/21 rear

csmeance
06-21-2012, 01:36 PM
I live in NYC , I don't want to go too low on the tires especially on 21'' rims...

Which set up is more "meatier" and acceptable? 245/35/21 & 285/30/21 OR 255/35/21F & 295/30/21R OR 255/30/21 front & 295/25/21 rear


First of all you have to remember that your sizing is VERY limited because if the tire is to big it's going to rub when you go over bumps or have a heavy load in the car.

The first number is PURELY the width of the tire in mm, so it would be 245mm -> 24.5 cm
The second number is the percentage of the width that is the sidewall height, so 30 -> 30% -> 7.3 inches
The third number is the rim diameter.

A 245/35/21 tire will have more sidewall height than a 245/30/21 tire but it will be the same width.
A 255/35/21 tire will have more sidewall(by 5%) and will be wider (by 10mm) than a 245/35/21.

Like I said before, a 245/35/21 and a 285/30/21 are required at a BARE minimum to make sure the speedometer stays accurate and you won't have rubber bands for tires. The only adjustment I'd make is in the width, if you change the sidewall ratios then the tire will be about 5% larger, and you shouldn't be going more than 3% as a rule of thumb because of rubbing and speedometer accuracy.

To answer your question, the MEATIEST tires I'd put on my car if it had the 21's would be this:

255/35/21 or 265/35/21 (front tires)
295/30/21 or 305/30/21 (rear tires)

And I'd pick 1 of each depending on the tires available and pricing in the size.

AngelE66
06-21-2012, 04:03 PM
csmenace,

Wow you're awesome! Thank you!

I have decided and to go with your first choice 245/35/21 for the front and 285/30/21 for the rears. Would that cause any rubbing issues with or without H&R Springs?


Also when I placed the order for the tires, I was told that I did not need TPMS as BMW 7series in 2004 didnt need any. Is this true?

csmeance
06-22-2012, 11:06 AM
csmenace,

Wow you're awesome! Thank you!

I have decided and to go with your first choice 245/35/21 for the front and 285/30/21 for the rears. Would that cause any rubbing issues with or without H&R Springs?


Also when I placed the order for the tires, I was told that I did not need TPMS as BMW 7series in 2004 didnt need any. Is this true?


That should not cause any sort of rubbing! As far as TPMS goes, it depends on how your car was optioned. The easy way to see if you have TPM is to go to your settings menu in idrive and under vehicle look for TPM or FTM. If you see TPM you have the little sensors that need replacement or need to be transferd to the new wheels. If you have FTM then you don' t need to do much! Simply mount on the wheels and under FTM just recalibrate it!