Now I know only a little about the Skyline suspension so this may not be relevent to you, but the fact is that most (all?) cars from Japan have lower supension bushes that are designed for use with rims up to a certain size, this is certainly the case with my Soarer and also the Supra, the standard rim size for both these cars [J-specs] is 16"rims, the Euro spec Supra has 17"rims but uses the same J-spec bushes.
The limit for good handling on standard bushes is 17" after this the whole thing deteriorates very rapidly as the tyres sidewall is reduced to less than 100mm [at that point tyre manufacturers increase the thread size of the strands of the tyre carcass) thus a greater shock load is tranmitted to the susp. and therefore the bushes are crushed at a highter rate and with greater deformity than designed for making the car less wieldy after ½ an hours driving, those of you with big wheels may notice this on a longish journey.
Go here for if you want a little bit on tyres;
http://www.jkwebdesign.co.uk/lexusclub/onallfours.htm
Please delete this if it is not relevent.