[Bay23]

I have a 2016 340xi with 400m 18"x8 all around and am going to need new tires soon. Wondering if I can run a 225/40/R18 instead of the stock 225/45/R18. Any one here have this setup, and or had issues with this?

[AspektUSA]

Why?

The 45 sidewall is great for bumpy roads and pothole mitigation.

It's a marked difference from my 442m summer set up.

[masterzapper]

You can mount a 245/40 but it will be 1% smaller in diameter, which means the speedo will be slightly off.

[alohasurftoad]

OEM 225/45/18=approx 26"
225/40/18= 25.1"

will it fit? sure...however you will increase the wheel gap you have now by 11mm, increase your speedo error 3.6% fast, accrue more mileage than actual by 3.6% (360 additional miles every 10000). if none of these things bothers you, have at it...

personally, i'd go the other way, larger 235/45/18. this will reduce wheel gap, speedo error and improve ride and impact protection. here is a link of this...https://f30.bimmerpost.com/forums/sh...+235%2F45%2F18
.

[Bay23]

Thank you for the insight. I am mainly just looking for a smaller sidewall for a more aggressive look. But if it throws everything out of whack it's not worth the trouble

[alohasurftoad]

as masterzapper stated, you could consider 245/40/18(25.7"). gap will increase just 4mm but with much more performance from a 20mm wider tire especially for B58 torque. it will look better if you are at least slightly, though.

here are links to cars with 245/40/18 square on OEM 18x8 ET34 397's which have the same specs as your 400M.
https://f30.bimmerpost.com/forums/sh...46&postcount=7
https://f30.bimmerpost.com/forums/sh...5&postcount=48

[janko990]

alohasurftoad nice said