These are mountain bike tires. I'm not sure why someone else put 80 psi in them to make it pop, I'm about 65 psi and good. I like that it's a complete set. 2 tubes, 2 tires. They fit easily, stretch on fine. TPI is for the terrain you'll be on. If you don't know what TPI is, then you won't care which you buy anyway. Only someone who rides alot on different bikes and tires will notice. If you have a cheap mountain bike and need spare tires, this kit is for you. If you are looking around for spare mountain bike tires, I'd recommend also getting one of those digital bike battery powered inflators too.