Not trying to get into kart racing or anything where I would need a competition spec kart; I’m just making something to use with my friends and was wondering about wheels and tires. I know that on regular cars the tires can be a fair amount wider than the rims, and I was wondering if this is also the case with karts. For example, would I be able to fit a tire with a width of 8 inches on a rim with a bead to bead width of 7 inches? Any additional information about wheels and tires is also welcome, I have a good amount of mechanical experience but no experience with karts.
The short answer is Yes. You can mount and bead an 8 inch wide tire on a 7 inch wide rim.
The long answer depends on what you are trying to gain. A wider tire on a narrower rim will give you a greater contact patch (aka more bite) with the road surface. It will also allow more flex in the sidewall which affects handling through the corners. More flex in the sidewall may not allow the back of the kart to rotate as well due to how the contact patch distorts when front is trying to take it in a different direction.
Depending on the power of the engine package you are using this make make the kart bind up and bog out of the corners. A TaG or Shifter kart on soft compound tires may not be affected as much as a LO206 or Stock Clone on harder compound tires would be. In these classes you often see a narrower tire on a wider rim (stretched) to help stiffen the sidewall and improve rotation.