Im looking to replace my rims with 18" Axis Hiros but what would I need to know in order to find a matching tire? I'm looking at Pirellis and they have a lot of choices but which should I choose? I'm looking for tires that have the same low-profile height to that of our tires. Any suggestions?

 

are you getting the 18x8.5? i saw the link you posted earlier. is that the only width available for 18's? if so, here are a few choices you can mount on those wheels.
235/40/18, 245/40/18, 255/40/18,
235/45/18, 245/45/18/ 255/45/18.

i would go for 245/40/18. if you need more info on what kind of tires works for you. check out tirerack.com they have tires that are rated by customers. the tires are rated on traction, cornering, wet traction, etc.

 

I'm assuming those measurements are unknown/outside diameter/inside diameter, correct? I've yet to figure out the first number

 

First number is the width of the tire in millimeters.

Second number is the "aspect" ratio. 40 means the sidewall height is 40% of the width or first number.

Third number is the rim diameter.

 

first number is the width of the tire in millimeters, at its widest point from sidewall to sidewall when mounted on the intended rim width. sometimes it's called the "section width".

second number is the Aspect Ratio. the number is derived by dividing the section height by the section width and multiplying by 100.

third number is the rim diameter.

so, for a pretty common tire, 215/65/15
the 215 is the width, sidewall to sidewall.
the 65 is the hieght of the sidewall, (the sidewall is 65% of 215)
15 is the diameter of the rim.

Here is a good site, if you want to see how one size tire comapres to another:
clinky dinky

 

Falken tires are the best IMO. The are made in japan, top rated by consumer reports and are fairly priced! I paid $100 a piece for 215/35/18 (ziexs 512's). They are quite on the highway, and do great in wet conditions!

 

So the middle number tells you the percent of the section height. The lower the percent, the thinner it is, right?

What about the width of the tire but on the inner side. If the rim is 18x8.5, how would I find a tire that's compatible with it? Obviously I would have to find a tire that has a 18" rim size but does the section width/aspect ratio help?

 

that is correct, a x/35/z tire will be a lower profile than a x/45/z tire. Note that x/35/z is NOT the same as y/35/w, i.e. the statement only works when talking about the same width and diameter numbers.

Best bet is to find a rim you like, then call a tire place, and ask them what size tires they would recommend putting on that rim. they'll give you plenty of ranges. then you can decide what size you want to go with.

 

http://www.tirerack.com/tires/tirete...e.jsp?techid=7

this should help you out