Normally, the new tires plus rims should not be more than +/- 3% of difference compared with the factory tires+rims. Otherwise, you could be caught by cops for speeding although your speedometer is says legal speed. Conversely, you might drive at <<100 km/h blocking up traffic although your speedometer suggests you are driving at a nice speed of 100 km/h :-) :-)
就个人经验,轮胎店和Costco都只推荐原厂尺寸。可以直接打电话给dealer,也可以自己上tire rack 网站查,输入maker, model and year, 选择tire/rim package, 就能看到不同的组合了。我的车原厂是18寸,冬胎就选的17寸,会便宜一点。轮胎直径大了1%,开起来没有区别。