Tire height mathematics

My old Kumho 165/80 had a calculated sidewall thickness of 132
My Douglas 205/65 was 133
I'm looking at a 185/65 which will be noticably shorter, 122 So, the thickness of the sidewall, from rim to outside diameter will be 122 (millimeters I think).

But what does this equate to in overall tire height? How much shorter will the 185 be than my other two tires?

a 185/70 is 129, but there is not very many tires this size....

you are right , BUT the manufactures don't do math.
when I was looking for a tire I took a tape measure with me and like Twin once said measure before you buy, and so i did,
and even if you go to the tire specs like tire rack you can see that a tire with the same numbers like 205/65r15 will have an inch of difference or more from tire to tire.

Sect. ,,,,,Tread,,,,,Overall
Width ,,,,Width,,,,,Diam.
8.2",,,,,,,,6.6",,,,,,25.5"
8.2" ,,,,,,,NA ,,,,,,,25.5"
8.1" ,,,,,,,5.7",,,,,,25.5"
8.2" ,,,,,,,7.4",,,,,,25.5"
8.2" ,,,,,,,8.1",,,,,,25.5"
8.2",,,,,,,,7.3",,,,,,25.5"

Now 205 millimeters is 8.07 inches
as you can see here from the numbers that I took from the manufactures specs. that you don't get 205mm .
and all these are 205/65r15 tires and most won't tell you just who wide there tire is.
I was looking for a size and i was thinking numbers , now i take a tape measure to get the size i want.
so here is the 185/65r15
Sect.,,,,,,,Tread,,,,,,Overall
Width,,,,,,Width,,,,,,Diam.
7.4",,,,,,,,,5.9",,,,,,,24.4"
7.4",,,,,,,,,5.4",,,,,,,24.3"
7.4",,,,,,,,,,6",,,,,,,, 24.5"
it looks like about an inch shorter , or sitting on your bike about a half ince shorter.

As for the 185/70r15 ........................
well i couldn't find any tires outside the racing tire line.
$$$ chaaa-chinngg $$$
I hope this helped, sorry for hijacking your thread.
good luck
Horse

horseman8m wrote:you are right , BUT the manufactures don't do math.
when I was looking for a tire I took a tape measure with me and like Twin once said measure before you buy, and so i did,
and even if you go to the tire specs like tire rack you can see that a tire with the same numbers like 205/65r15 will have an inch of difference or more from tire to tire.

Sect. ,,,,,Tread,,,,,Overall
Width ,,,,Width,,,,,Diam.
8.2",,,,,,,,6.6",,,,,,25.5"
8.2" ,,,,,,,NA ,,,,,,,25.5"
8.1" ,,,,,,,5.7",,,,,,25.5"
8.2" ,,,,,,,7.4",,,,,,25.5"
8.2" ,,,,,,,8.1",,,,,,25.5"
8.2",,,,,,,,7.3",,,,,,25.5"
Horse

Been trying to get my head around what you said here......

What I think you said is that if I buy a 15" tire, it's going to be 25.5" in overall diameter...no matter the tread or section width. That all the math I'm doing is to no avail.

That 205 may or may not be 205 - I need to measure the tread to know what width it REALLY is.

That 0.65 x 205 may not equal 133.25. So, I can't rely on the % number as anything more than an approximation. I need to measure the tire and trust the ruler and not the numbers stamped on the tire.

Did I get this right? Good info for us number crunchers. We expect things to add up.... It's good to know not to expect them to when it comes to tire sizing. And this all makes sense to me now. Cuz I was wondering how the rear speedo could ever work on any bike if the tires were all different diameters.

you Hit it on the head with that one .
Don't count on the size being the real size.
It can very from tire manufacture to tire manufacture, even from the same tire manufacture and different make.
good luck
Horse