[chris_ss]

hello,

has anyone tried running 275/40/20 and 245/45/20 tires on a g30 on 668M wheels?

I'm apparently going through $2500 of tires/year due to potholes and road conditions, maybe increasing sidewall size would help. a tire size calculator seems to indicate that the width would remain the same but the overall diameter would go up about an inch.

The speedometer would be off, but maybe the computer is able to accomodate for that.

thanks!

[Volasko]

I'm running this setup, with agressive spacers and eibach lowering springs and do not have any rubbing issues. The ride quality is definitely improved with the extra sidewall. I would highly recommend doing this.

[1gkek]

Just picked up my 550i and I'm looking at alternate aspect ratios as well. This site will show you the speed differences at different tire sizes.

https://tiresize.com/calculator/

Comparing the 245/45 to the stock 245/35, At 80mph indicated actual speed is 85.7mph. You do get almost an entire inch of extra sidewall though.

[ezaircon4jc]

Originally Posted by 1gkek

Just picked up my 550i and I'm looking at alternate aspect ratios as well. This site will show you the speed differences at different tire sizes.

https://tiresize.com/calculator/

Comparing the 245/45 to the stock 245/35, At 80mph indicated actual speed is 85.7mph. You do get almost an entire inch of extra sidewall though.

Try 245/40. A BMW's read 3mph over by design, at an indicated 80 you'll actually be going just under 83, so the speedo will actually read pretty close to actual speed. I'm vacillating doing just that on the 759i's I just purchased, going to a 245/40 vs. the stock 245/35.

[1gkek]

Good catch on the typo, thanks.

[SonD]

By law in the Uk / Europe, car speedos must over tell the speed, never under what is actual.
Over here for certain, an indicated 30 would probably be 27 / 28mph.
An indicated 80 would be 76 - 78 never, ever 83 over here.
At least, with legal sized tyres & rims.
Mess with them, and you could end up on the wrong side of a big fine.

[chris_ss]

Originally Posted by ezaircon4jc

Try 245/40. A BMW's read 3mph over by design, at an indicated 80 you'll actually be going just under 77, so the speedo will actually read pretty close to actual speed. I'm vacillating doing just that on the 759i's I just purchased, going to a 245/40 vs. the stock 245/35.

fixed

[ezaircon4jc]

Originally Posted by ezaircon4jc

Try 245/40. A BMW's read 3mph over by design, at an indicated 80 you'll actually be going just under 83, so the speedo will actually read pretty close to actual speed. I'm vacillating doing just that on the 759i's I just purchased, going to a 245/40 vs. the stock 245/35.

Originally Posted by chris_ss

fixed

Thanks. Yeah... I meant to say that with the 45 series tires the speedo would read more true to actual speed.

[WretchedRefuse]

Originally Posted by chris_ss

...I'm apparently going through $2500 of tires/year due to potholes and road conditions, maybe increasing sidewall size would help. a tire size calculator seems to indicate that the width would remain the same but the overall diameter would go up about an inch. ...

Or consider 19" wheels with non-RFT tires. That might yield better results than taller tires without affecting your speedometer.