19inch..?

[WARNSTER]

A very quick question.

I thinking of whacking some 19inch BBS alloys on my Z3m Roadster.
They look pretty mean but will it have much effect on the ride, or should i just stay with the 17's?

Cheers.

W

[mmm-five]

If you go to 19's then you're also going to have to go to 19" 35 profile rubber, which will cost a lot more than the 17's (e.g. 17" PS2 for £110, 19" for £180).

Also, as you've reduced the profile, you'll upset the suspension as it was set for a specific (or very close) size combo.

If you don't mind a bone jarringly hard ride, and like less progressive feeling to the handling then go for it!

[The_Doc]

IIRC your speedo mph will be wrong(-er) now that the circumferance of the wheels has changed.

It will read too low (or is too high, my brain hurts...)

[The_Doc]

Its too low.

In a fictitious car, with 100cm circum wheels doing 1 wheel revolution in 2 secs.
The car will measure you have travelled 1 circumferance (100cm) in 2 secs and calculate speed as 0.5m/s

New wheels are let's say 150cm circumferance. Keeping the revolutions the same at 1 complete turn in 2 secs (ie drivesharft and engine turning at same speed as before) the new speed is actually 0.75m/s.

BUT.... the speedo will read the same as before. So it is reading low

you'll need a GPS speedo to recalibrate and make sure you don't get flashed by a 30mph camera.

[Beemer-5]

Bigger wheels plus lower profile tyres equals correct speedo readings, or at least as close as makes no difference.
BMW do options for wheels on most models and they never bother changing the speedo.

EG. 535d. I had the optional 19s.
My one would have had the same speedo readings with 17, 18 or 19 inch wheels.
As the diameter grows, the profile reduces. Overall wheel size is virtually identical.