Once had a similar prob, going to crail one year, I had to put 2 s1 rims on the back of a 4x4 saff and swap the 17's to the front due to 2 punctures on the front 17's, I didnt have another 17" rim and the s1 rims not clearing the front brakes.

Looked VERY shocking, drove Very badly,but still the car got one hell of a hammering that day .