metric to english conversions

does anyone have a chart or something to convert english tire sizes to metric, or vise versa? sorry, if it is hasta , i searched

Well...

I don't know if this is a direct conversion or what you're really after, but here goes...

Example size - 255-75/15.

Read as: "255 mm tread width, 75% aspect ratio, for a 15" rim."

Meaning:
The face of the tread is 255 m/m wide. Divide by 25.4 to get 10.04-ish inches.
Take the "aspect ratio" (75%) and multiply by tread width to get sidewall height (255 x .75 = 191.25m/m, 191.25m/m / 25.4 = 7.5-ish inches)
Therefore, we have a 10" wide tyre, and we're about to find out what the diameter will be...
Take twice the sideall height (7.5" x 2 = 15") and add it to the rim diameter (15") for the total nominal rolling diameter (15" + 15" = 30". It's actually a touch less, but that's going to vary based upon inflation pressures, vehicle weight, and vehicle loading.)

Make any sense now?

5-90

5-90 said:

Well...

I don't know if this is a direct conversion or what you're really after, but here goes...

Example size - 255-75/15.

Read as: "255 mm tread width, 75% aspect ratio, for a 15" rim."

Meaning:
The face of the tread is 255 m/m wide. Divide by 25.4 to get 10.04-ish inches.
Take the "aspect ratio" (75%) and multiply by tread width to get sidewall height (255 x .75 = 191.25m/m, 191.25m/m / 25.4 = 7.5-ish inches)
Therefore, we have a 10" wide tyre, and we're about to find out what the diameter will be...
Take twice the sideall height (7.5" x 2 = 15") and add it to the rim diameter (15") for the total nominal rolling diameter (15" + 15" = 30". It's actually a touch less, but that's going to vary based upon inflation pressures, vehicle weight, and vehicle loading.)

Make any sense now?

5-90

Click to expand...

Basically correct, except the primary width isn't the face width of the tread, it's the maximum cross-section width at the bulge in the sidewall. Check a bunch of manufacturers' tire specs and you'll see that for tires of one size, the tread width varies tremendously.

XJAnthony said:

does anyone have a chart or something to convert english tire sizes to metric, or vise versa? sorry, if it is hasta , i searched

Click to expand...

If you have a Java-enabled browser, the Miata Club (of all people) have a very useful online applet for doing just that:

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

It only goes up to 335-width tyres, but does display the US Standard equivalent as well.

Eagle said:

Basically correct, except the primary width isn't the face width of the tread, it's the maximum cross-section width at the bulge in the sidewall. Check a bunch of manufacturers' tire specs and you'll see that for tires of one size, the tread width varies tremendously.

Click to expand...

Really? Not to doubt you - but do you have a couple links handy? I'd originally learned it as tread width (granted, that was a Kragen's - which also make the information suspect...)

Besides, the idea of taking the width as "the maximum bulgs in the sidewall" seems specious to me - that will vary greatly, again, with inflation, vehicle weight, vehicle loading, ...

5-90

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=53
.
http://www.oly4x4.com/4x4calculators.htm

awesome, thanks a lot guys

http://www.jeepclub.co.uk/faqs.cfm?id=2
http://www.jeepclub.co.uk/tyrecalc.cfm

English? English????!!!!!! :laugh3:

5-90 said:

Really? Not to doubt you - but do you have a couple links handy? I'd originally learned it as tread width (granted, that was a Kragen's - which also make the information suspect...)

Besides, the idea of taking the width as "the maximum bulgs in the sidewall" seems specious to me - that will vary greatly, again, with inflation, vehicle weight, vehicle loading, ...

5-90

Click to expand...

It doesn't vary with vehicle loading, because the manufacturers rate each tire on one specific rim size, at the recommended "standard" pressure (whatever that is). Field differences due to loading, tire pressure and rim width do change the actual cross-sectional width, but not the nominal size.

Most manufacturers' specs tell you what rim the rated size is based on.

http://www.offroaders.com/tech/AT-MT-Tires/tire-tech.htm#Tire_Width

http://www.pneusmetro.com/ENglossary.html
http://www.discounttire.com/dtcs/infoTireTerm.dos

http://www.hoosiertirecanada.com/racingtires/dimterms.htm

Going through the widest section (sidewall to sidewall) still doesn't make too much sense to me, but what do I know? It just seems like there are too many variables to worry about going through there. Go figure.

You learn something new every day, right? I wonder where they originally got my misinformation from...?

5-90