Wheels

Changing the size of your rims often means having to figure out what tyre size you need. The problem with changing the wheel size is that without getting the appropriate tyre size your speedo can be out of whack. Figuring out what tyre size you need to maintain the effectiveness of your speedo requires some basic maths. Here are a few online calculators for tyre size and other wheel measurements including offset.

One of the best is from Miata.net (Miata's are a USDM MX5). It has a nifty visual representation of the tyre versus wheel size for new versus old combination. Here is an example for my situation of wanting 20in rims on my BF XR6 ute:

Another site, Car Bibles, has a page of calculators for every conceivable calculation possible when it comes to figuring out changes in the wheel tyre combination, including offset.

Here is another calculator linked to an online tyre shop that lets you know if there are any actual tyres in the size you are after, which is very handy.

I am going to have rethink the wheel/tyre combination for my ute if I want to retain the load capacity.