Just found this invaluable little tool for calculating overall diameter with different wheel/tyre sizes.....
http://www.unixnerd.demon.co.uk/bmw_wheels.html

This is slighty the same but also calculates the perimeter % different (swedish language):
http://www.nordicaudi.com/index.htm?faq/falg-dack/000416_berakning/main_index.htm

And this wheel offset calculator: http://toy4two.home.mindspring.com/offset.html

/Patrik

__________________
Patrik Sjoblom....1993 MB 320 CE......Bought Jan 2001. Only 16.8 mpg
Stockholm.........Silvermetallic....DEFA immobilizer/alarm + Original larm
SWEDEN............17x7.5 ET35 wheels with 215/45-17 Kumho 712 ECSTA .

This one probably uses the same computer algorithm, but also shows a drawing of the tires from the side and from the edge to show you the differences between 2 sizes.

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

__________________
John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E

Here's another one.

Tire Section Width in MM / 25.4 X Aspect ratio (.70 for 70 series) X 2 = Rim Size (15 for a 15 inch wheel)


Example 205 R55 - 16

205 \ 25.4 = 8.07 X .55 = 4.44 X 2 = 8.88 + 15 = 23.88

23.88" Diameter

This one works even with no computer in sight.


Hope this helps,

When looking for specs for ratios and mph a rolling diameter is
sometimes useful and accurate for the specific vehicle.
Easily fiqured by inflating tire to your liking, marking sidewall to ground, move ahead one rev. for second mark.


This distance is the rolling circumference. Divide by pi [3.1416]
if you need diameter.

I like the wheel offset calculator, and use the same one, but a better place (IMO) is this calculator:

http://www.paspeedo.com/calculator.htm

tells you just about what you might want to know. Good luck.

__________________
Chirag (Charlie) Patel
--------------------------------------------
- 03 Mercedes S600 Sport TTV12
- 97 Acura NSX-T
- 99 BMW E36 M3 w/500+ HP
- 04 Lexus RX330
- 04 Dodge Dakota Quad 4x4 V8

4 Sale:
- 99 BMW M3 E36 Coup with Dinan SC, Upgraded to an RMS Stage 3 with Aftercooler, 12psi, and 500+hp @ flywheel.