I have a 1995 Nissan pickup with tires 225/70/14.
My question is more general. Does it require modification to increase tire and rim size or can they simply be put on? Like could I just purchase 16" rims and appropriate tires or would the tire hub need to be changed? Of course, I know this is dependent on the space between the tire and wheel well. Just want to know if it's as simple as measuring this space or other mods are required.
As far as wheel to hub clearance, if you increase the size of the rim, you won't have fitment issues there. Mind, you need to worry about offset and backspacing concerns, but in general, you won't have fitment issues because you'll have more space between the rim and the hub.
As far as wheel well, you're correct. You need to measure how much space you'll have and provide more if needed through a body/suspension lift, or what have you. There's also some worry not only for height, but for when the front wheels are turned to ensure proper turning radius.
The other area you may need to consider is the effect on gearing : larger rolling radius tyres will reduce acceleration but increase top end speed.
A tire size comparison will give you an equivalent rolling radius while changing from 15 to 16 or more if possible.
Here is one, of many, sites that do the comparison :
