I'm sorry, I'm a little new with tires and wheel setups. Can someone please explain the "Series" on tires? I understand the width/aspect ratio/diameter system, and now how the offset works. I just don't understand how series comes into play or is calculated. Apologies for my regressive noobness. Tires and wheels are a strange new world for me and I'm the guy in the Red Starfleet uniform. (Excuse the pun, I'm such a nerd).

...actually the "series" & aspect are the same. The lowerer the #, the thinner the tire...hope this helps some

So I've seen people reference cross section as like 8 inches, for example. So that means 8 inches across the contact surface of the tire, right? So hypothetically, what is 8 inches equivalent to in the series number? Thanks.

...ok let me start over & see if we can get all the questions answered....in your 1st post, you mentioned width,aspect & diameter.Using the stock tire (245/40/18)...245 would be the width...40 would be the aspect or "series" & 18 would be the diameter...when someone reference the cross section, usually they're talking about the width of the rim...so in your hypothetical question, the 8inches wouldn't have anything to do with the series...

Awesome, I totally understand now. Thanks for the clarification! I'm up to speed now.

Keep in mind.....you're new tire setup needs to be within 3% of the stock overall diameter of the factory tires. As your wheel diameter goes up, the aspect ratio goes down, thusly the sidewall gets smaller in order to keep the overall outside diameter within tolerance.

A correct tire size for 20's as an example is 235-30-20 and 245-30-20 but that's just an example. Both fall under the 3% threshold.

Play with this application.... http://www.1010tires.com/Tools/Tire-Size-Calculator