[bmwmike01]

Hi,

So I noticed for 668m m550 rims there is only like 1-2 choices for all season tires. However, I was reading somewhere that its fine to increase the side wall size 245/xx/20 (the second number) by 5 for the rim in this car, which opens up more choices and will give better comfort when driving.

What would be the negative effects of doing this? You have enough clearance to increase the side wall by 5 so fitting won't be the issue.

[AP]

wouldn't that make the speedometer read incorrectly? (unless the tyre choice in idrive does clever stuff and adjusts accordingly?)

[bmwmike01]

Originally Posted by AP

wouldn't that make the speedometer read incorrectly? (unless the tyre choice in idrive does clever stuff and adjusts accordingly?)

I think if you have the ratio remain the same and increase by front and rear by 5 it shouldn't throw it off?

[lemetier]

Originally Posted by bmwmike01

Hi,

So I noticed for 668m m550 rims there is only like 1-2 choices for all season tires. However, I was reading somewhere that its fine to increase the side wall size 245/xx/20 (the second number) by 5 for the rim in this car, which opens up more choices and will give better comfort when driving.

What would be the negative effects of doing this? You have enough clearance to increase the side wall by 5 so fitting won't be the issue.

Just the front?

[bmwmike01]

Originally Posted by lemetier

Just the front?

No. Both the front and the rear by 5.

[lemetier]

Originally Posted by bmwmike01

No. Both the front and the rear by 5.

You can but I don't really see the point unless you really want Pirelli or Yokohama over the Conti and Michelin.

[bmwmike01]

Originally Posted by lemetier

You can but I don't really see the point unless you really want Pirelli or Yokohama over the Conti and Michelin.

The only 2 choices for all season tires are continental and Michellin however my reasoning for this is to provide more comfort and protect myself a bit better against potholes since the sidewall will be bigger.

[.BMW.]

Will fit fine, no issues!

Better comfort, improved wheel protection and a more accurate speedo (since it reads high with OEM tire sizes).

[bmwmike01]

Originally Posted by .BMW.

Will fit fine, no issues!

Better comfort, improved wheel protection and a more accurate speedo (since it reads high with OEM tire sizes).

The dealer told me the gear ratios would be thrown off and the transmission would get damaged if I do that? Are they full of shit?

[.BMW.]

245/35-20, dia. 680mm
275/30-20, dia. 674mm (0.9% shorter)

245/40-20, dia. 704mm
275/35-20, dia. 700mm (0.6% shorter)

The taller tires, also used on 7 Series, actually has better matched diameters!

[bmwmike01]

Originally Posted by .BMW.

245/35-20, dia. 680mm
275/30-20, dia. 674mm (0.9% shorter)

245/40-20, dia. 704mm
275/35-20, dia. 700mm (0.6% shorter)

The taller tires, also used on 7 Series, actually has better matched diameters!

Hmm that's interesting. I feel like the people in this forum are more knowledgeable than the dealers service dept. I wonder why Bmw doesn't approve this size since it's a better match.

[lemetier]

Originally Posted by bmwmike01

The only 2 choices for all season tires are continental and Michellin however my reasoning for this is to provide more comfort and protect myself a bit better against potholes since the sidewall will be bigger.

Slightly more sidewall but a stiffer (higher load rating) which is cancelled out by TPMS calibration so it's a wash. If you want comfort and added sidewall, a -1 19" or better yet a -2 18" would be the direction to go.

Originally Posted by bmwmike01

The dealer told me the gear ratios would be thrown off and the transmission would get damaged if I do that? Are they full of shit?

Yes they are. Tire data for the rear axle is input via iDrive for TPMS and during initialization, determines the appropriate pressures and front axle speed difference.

[Short540]

I'm running 255/35/20 in front and 285/30/20 in the rear. Which gives me sidewall protection because I went with a wider tire. So it's a percentage of the width. 35% of a 255 wide tire gives more sidewalk protection than a 245/35/20 tire.

[Short540]

Looks really good from the rear. But from the side on the rears it looks like a little too much tire. I prefer the continentals look over the pilot all seasons. But it rides and takes bumps smoother with the pilots. Catch 22 I guess lol