Got 215/45R17 Nokian WR G4 installed on the JCW a couple days ago, getting ready to do a long trip to Vermont.
The current set up is 18mm higher than the stock size of 205/45.
Regardless the donut is significantly shorter than even the OEM size, with my slightly higher ride height would this work
for short distance as long as I go below 50mph?

In the long run, should I find a replacement donut that's about 18-20 cm taller?

 

 

Toss the odd sized tire on the rear since your drive/steering wheels are up front. If the traction control complains about the wheel speed differences turn it off. Car may handle a bit odd but should be perfectly safe to drive to get the tire repaired/replaced.