I heard that different tire brands have different sidewall heights. For example a bridgestone tire would like fattier then a yokohama. Or something like that, is this true? If so which tire looks the thinnest? Sorry if thats such a noobie question, im really new at this.

 

Yeah, different manufacturers can have slightly different diameter tires even when the listed measurement is the same. So if you have two different brands of 255/40/18 tires, Brand A could be 25.9", and Brand B could be 26.1". However, there's usually very little difference. Any differences will be minor. If you want to be sure, you'll have to look at the listed specs for each tire on the manufacturer's website. For each tire your after, just pull up the specs, find the size you're after, and look at the diameter of the tire and compare it to other brands of that same size. Usually they'll be within about .1" of what the measurement says they're supposed to be.