Rim Size Differences

[ShiftTab]

I'm a complete noob to rims and their sizes. So I'm wondering what the differences between 18x7.5 and a 18x.8 (I always thought when you buy rims, it's just 18" and that's it).

And tires, what do these three sets of numbers mean? 225/45/18And is a higher treadwear better or a lower better?

I guess what I'm asking is if anyone could go through a step by step in how to make the right purchase. What I should be looking for when I'm thinking about purchasing a certain size?

I appreciate it guys!

[spockrock]

I'm a complete noob to rims and their sizes. So I'm wondering what the differences between 18x7.5 and a 18x.8 (I always thought when you buy rims, it's just 18" and that's it).

And tires, what do these three sets of numbers mean? 225/45/18And is a higher treadwear better or a lower better?

I guess what I'm asking is if anyone could go through a step by step in how to make the right purchase. What I should be looking for when I'm thinking about purchasing a certain size?

I appreciate it guys!

With rims there are three things you need to look at Diameter width and offset. Diameter you know its the "height" of the rim, width is the width of the wheel and offset is how much the wheel hub is offset from the center of the wheel. For example my rims are 18x8.5 +38, that means my rims are 18's and are 8.5 inches wide. The plus 38 is more difficult to explain, but you should use a wheel calculator to figure out how much further or in further your wheel sits. The stock 3.5 wheel is 17x7 +45 so with the +38 offset my wheel sits more flush with the fenders.

Tires its width/height/Diameter, so my tires are 245/40/18 so the first number depends on the width of the new rim, since my rims are 8.5 inches wide I went with 245 tires, 40 is a percentage of the width, so the height is 40% of the width of the tire and the last number is the Diameter, which has to match the diameter of the rim. Also use a tire calculator to figure out what size tire you need.

[mcheddadi]

http://www.powerdog.com/tiresize.cgi

the wheel calculator I use

the offset is like this:

[ShiftTab]

Thanks I appreciate it!

[SniperJoe]

Two other tire size calculators ... Both with good info:

http://www.wickedbodies.net/Ti...r.htm

and

http://www.miata.net/garage/tirecalc.html

[mrodrig2]

is a higher treadwear better or a lower better?

A higher wear rating is better assuming that you want to replace your tires as infrequently as possible. Wear ratings are comparable within a brand but not necessarily across different brands The number represents the manufacturers expected average lifetime of the tire relative to that company's control test tire. So for example, a tread wear rating of 200 indicates that the tire is expected to have 2 times the life of the mfg's control. A tire with a rating of 400 from that same company would have twice more life than the 200, but a 400 rated tire from a different tire might have more or less depending on their own standard.

[Rob.Vegan]

wow this must be a record for not longest thread without anyone mentioning that there is a whole Rim/Tire section on these forums...

congrats

[spockrock]

I was going to say, use the flashing search button but I then, meuh....

[Kanard]

why cant we just order some 18s and be done with it? lol That stuff is confusing. but i see what ppl are saying. . lol *i wanted to know too. so good thread*

[spockrock]

why cant we just order some 18s and be done with it? lol That stuff is confusing. but i see what ppl are saying. . lol *i wanted to know too. so good thread*

You can but if you don't pay attention it may not fit properly and or you get the wrong tires and your speedo and odometer are off.

[ShiftTab]

You can but if you don't pay attention it may not fit properly and or you get the wrong tires and your speedo and odometer are off.

what is a typical set up example to follow to make sure the rims and tire size you get will not affect your speedo and odometer?

[xeene]

there is no typical, you pick your wheel size and then use http://www.miata.net/garage/tirecalc.html to find the right size of tire that you'll need so it comes as close to stock as possible.

[ShiftTab]

I really want to get some 18s but my car has 17 stock. Is it possible to make 17s look just as good?