What are the widest tyres you can put on a BMW 5 series?

[JAFOOLY]

It has 18" alloys. Not to fat and wide but something nice.

 

[Hawkeye85]

You can only go as wide as your rims!!!! You can really only go for standard, terrain or low profile NOT how wide and fat you can get them!!!

 

[Hawkeye85]

You can only go as wide as your rims!!!! You can really only go for standard, terrain or low profile NOT how wide and fat you can get them!!!

 

[gojuryu]

Beamers don't have a good ride to start with. If you put too low a profile a tyre on the ride will be even worse.
OK it will go round corners at 100 mph but you will end up with a sore arse every time.
Tyre shops will advise on the best compromise to fit your rims.