Calculating tire height

I picked up a Chevette. Stock tire size is 175/70R13 with a diameter of 22 1/2". It came with hideous American Racing 14" wheels. They have 185/60R14s with a 22" diameter. I picked up a set of 15" 2005 Mini Wheels ($100!) with stock 175/65R15s. They have a diameter of 23 1/2" and look even bigger. I want to get some tires around 22" but don't want to go through a lot of expensive trial and error. How can I figure out the installed diameter? Should I just start measuring random tires in the tire store or parking lot?

I'm thinking maybe 195/50R15.

Plug in sizes in the Miata.net tire calculator, or find the size you are looking for at Tire Rack and look at the specifications chart and it will list the diameter.

There are several tire size calculators out there. Miata.net has one. Here is another.
Another tire size calculator

Thanks! I knew they existed but always forget where.

The geek in me wants to point out that you can figure it out yourself. For example your 15 inch tires are 175/65 15. 175 is the width in mm. 65 is the percent of that width in sidewall height. 175mm divided by 25.4 gives you ~6.89 inches. That times .65 gives you a sidewall height of ~4.48 which I'll round off to 4.5 inches. 4.5 plus 4.5 plus 15 inch wheel gives you 24 inches. Or you can hit the easy button and use the calculator.

You can do the math too.

175/70R13

Section width 175mm or 6.89"

Tire height 70% of width, so 175*.70=122.5 or 4.82"

There is tire on top and bottom of the 13" rim, so 4.82+13+4.82=22.64" total diameter.

Edit, type too slowly with one finger!

Search the web for an excel file. RacingFormulas.xls It was written by Earl Parker Jr a tuning and carburetor wiz. It has tons of good useful calculators. If you can't find it PM your e-mail.

How close do you want to be?
There's a fair amount of variation in actual size vs what it says on the sidewall.
Each tire is mode on its own set of molds, so it's whatever the manufacturer builds.
Any calculation is an educated guess, trumped by actual measurements.

True and tirerack list the actual size for the tires they carry.

as does every store that sells tires... just walk into a reputable locally owned tire shop and tell them what you are doing... you will have the best luck at the one with the custom car parked out front that has big wheels on it, since that guy knows a thing or two about non stock tire sizes..

he might bust your balls about putting wanting to put 15" tires on a berkeleying Chevette for some reason, but just roll with it..

185/60-14 should be a hair taller than 175/70-13. But it wss the factory plus one upgrade size in the 80's.

http://www.1010tires.com/Tools/Tire-Size-Calculator/175-70R13/185-60R14/195-50R15

195/50-15 was the standard 15" size to replace those but it got hard to find all of the sudden.

tire size (185) times aspect ratio ( 60%) times 2 divide by 25.4 (mm/in.) plus wheel diameter. Come out same as listed sizes on tire rack.

Here's a tire calculator I wrote: http://nondisplayable.ca/tire-calculator/

Need to add more stuff to it one day (like a +1 wheel size finder). Let me know if it sucks.

This thread reafferms my hatred of tire sizing. Tred width in milimeters, sidewall height as a percentage, and the rim size in inches. Da-fuq?

Tires dimensions are the one case that metric made worse.

Just remember none of these are accurate to the size of the tire. They are just a reasonable approximation.

Michelin tends to run a little tall, coopers were a little short (oh so many years ago).

Didn't old bias ply tire sizing not include any height indication though?

Radial slicks are often measured with a metric height instead of a percentage, like 280/650/18, with the 650 being overall tire height, which makes a lot more sense.

I like old school truck tires. You want 33" tall tires that are 12.5" wide on 16" wheels? You want 33x12.5 R16. What berkeleytard decided, that was too easy, lets make 'em do some math.

Cheater slicks and Super Swampers seem to be the only way to get old school size numbers anymore.