Changing tyre sizes ( aspect ratio )

[Sump]

Lexus comes with 245 45 18. If I fitted 245 40 18 would there be any serious issues? It calculates it as a -3.55%..

[HustleRussell]

Change all four at the same time so the ABS/TCS doesn't get confused and it'll be fine (assuming you can live with the speedo overreading even more than it does already, reduced MPG, reduced ride comfort etc etc.

[davepoth]

My guess is that it really wouldn't help the ride very much. You'll also lose a bit of ground clearance. Speedo will over-read, which is fine.

[Sump]

It's on a Lexus so it doesn't bother me and overreading is fine.