I have two sets of tyres for my 4x4 Hilux
205R16 & 31x10.5R15

what do these figures mean? How do you work out the dimensions of your tyre from these?

also I'm fairly sure these are 15inch tyres, I want to get bigger tyres, 16's, will the vehicle be able to handle bigger tyres without any problems?

''205R16'' Usually there is a third number like the P205 55 16's on my car. ''P'' means passenger, the tire is 205 mm wide, and fits on a 16'' rim, yeah, consistent. The 55 means it is 55% as high as wide. 205mm/25.4mm/in(.55)(2) + 16 gives you the overall diameter in inches. I think that is what the 31 in ''31x10.5R15'' is, 10.5'' wide, and fits on a 15'' rim.

Usually you can use a slightly larger tire without it rubbing the wheel well, or only slightly on bumps and turns.