for those running aftermarket 21's on M6 - Proper size tires for 21's

[LSM]

21x9.5 fronts and 21x11 rears...I know people go with 265/30/21 fronts and 305/25/21 rears but if you go with the 295/25/21 rears the overall diameter and revolutions are more similar..Thoughts?? What are you guys running?

Thanks

Lou

[Hunter5179]

You are good either way. I would go 305 in back. That is what I am running also.

[LSM]

Originally Posted by Hunter5179

You are good either way. I would go 305 in back. That is what I an running also.

Yea thats the dilemna, 305's fit 11" rear better but the 295's more closely match the overdiameter and revolutions

[johntclark]

The 305 matches better than the 295. Just check the specs of who your buying from. I don't think anyone but Michelin make the 305.

[RiverRunner]

My speedometer is over by 7%, so if the tire diameter is 7% larger, the speedo would be correct. Maybe worth checking on your car before worrying about matching the diameter.

[LSM]

Originally Posted by PackerFan

My speedometer is over by 7%, so if the tire diameter is 7% larger, the speedo would be correct. Maybe worth checking on your car before worrying about matching the diameter.

be close in overall diameter is important as are the revs per mile which is based on OD etc....Thats why I was wondering.

265/30/21 - overall diameter 27.3 - revs per mile 762
295/25/21 - overall diameter 26.8 - revs per mile 776
305/25/21 - overall diameter 26 - revs per mile 799

Stock
265/35/20 - overall Diameter 27.3 - revs per mile 761
295/30/20 - overall diameter 27 - revs per mile 770

[RiverRunner]

Originally Posted by LSM

be close in overall diameter is important as are the revs per mile which is based on OD etc....Thats why I was wondering.

265/30/21 - overall diameter 27.3 - revs per mile 762
295/25/21 - overall diameter 26.8 - revs per mile 776
305/25/21 - overall diameter 26 - revs per mile 799

Stock
265/35/20 - overall Diameter 27.3 - revs per mile 761
295/30/20 - overall diameter 27 - revs per mile 770

I understand that, it's directly proportional to the OD/Speedometer, looks like the 305/25/21 will make the issue worse. Most of our Speedometers are off by 5-10%, (over). I was told that the OD is correct, and that the Speedometer has to be over to meet some European law. I think it's BS, they should make the it correct with new rubber, it will increase as the diameter decreases (RPM increases).

[LSM]

Originally Posted by PackerFan

I understand that, it's directly proportional to the OD/Speedometer, looks like the 305/25/21 will make the issue worse. Most of our Speedometers are off by 5-10%, (over). I was told that the OD is correct, and that the Speedometer has to be over to meet some European law. I think it's BS, they should make the it correct with new rubber, it will increase as the diameter decreases (RPM increases).

Is it only the speedometer that is effected? I thought effected the traction control and other things?

[RiverRunner]

Originally Posted by LSM

Is it only the speedometer that is effected? I thought effected the traction control and other things?

My point is that the speedometer is off with the factory rims/tires, over by 7%.

[LSM]

Originally Posted by PackerFan

My point is that the speedometer is off with the factory rims/tires, over by 7%.

I got your point, I was asking another question thought you might know

[Tom@SonicMS]

I think the 26" OD on the 305/25/21 is wrong. Its should be 27".

(305x25%)x2 / 25.4 + 21 = 27" which is closer to stock.

[LSM]

Originally Posted by Darwin@SonicMS

I think the 26" OD on the 305/25/21 is wrong. Its should be 27".

(305x25%)x2 / 25.4 + 21 = 27" which is closer to stock.

You are correct in that. When I was considering 21's it seems everyone on this board runs the 305/25/21 which is 26 OD. The better fit is the 295/25/21 which is 26.8 OD...