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Message started by norm92de on 12/12/15 at 17:11:11

Title: circujmference of rear tire.
Post by norm92de on 12/12/15 at 17:11:11

Basic question I know.
Has anybody measured the circumference of the stock rear tire?

Thanks.

Title: Re: circujmference of rear tire.
Post by justin_o_guy2 on 12/12/15 at 17:20:42

Basic question? And what manufacturer? What is the tire size and aspect ratio? Have you considered marking the tire and floor and rolling it, and measuring,?

Title: Re: circujmference of rear tire.
Post by Art Webb on 12/12/15 at 19:21:59

Ahem!

3D3C213E6A613736530 wrote:

stock rear tire?

Thanks.

Title: Re: circujmference of rear tire.
Post by justin_o_guy2 on 12/12/15 at 19:29:17

Well, I don't have one. And the answer is as easy as a mark, roll, measure.
I Did focus on the question of
Is this a Basic question? And, brainlocked..
I'm good at that.
Spelling test, seventh grade.
I never got below a ninety, so,,I didn't check my work.

Teacher calls out the word

Shed

And, as I wrote the sh, I was thinking, sardonically, the next word will be Real tough, like It, maybe,,
And, I Wrote It, right after I wrote sh, and turned it in...
Ooppsies,
I explained it, he was cool..but he Did call me, rather urgently, to his desk.

Title: Re: circujmference of rear tire.
Post by Art Webb on 12/12/15 at 19:34:04

Sounds like something I would do
and yup, that's the simple
there's a formula for figuring it
But
Some of the makers don't exactly mark the side wall with the REAL dimensions, so rolling IS the best way

Title: Re: circujmference of rear tire.
Post by Kris01 on 12/13/15 at 06:56:31

According to the calculator, a 140/80-15 is:

23.8189" tall
5.5118" wide
and has a circumference of 74.8293" (or 6' 2.83")

Manufacturers are not that exact though. You WILL find differences in brands and models from what the calculator says.

Title: Re: circujmference of rear tire.
Post by norm92de on 12/13/15 at 08:18:00

Didn't mean to start an argument.
By stock I mean an IRC 140/ 80- 15.
I thought somebody would have already measured it and recorded it somewhere.

Thanks for your answer Kris.

Title: Re: circujmference of rear tire.
Post by Kris01 on 12/13/15 at 08:21:24

I'm curious why you need to know. Are you setting a bicycle speedometer/computer to read correctly?

Title: Re: circujmference of rear tire.
Post by Serowbot on 12/13/15 at 08:29:48

How many miles on the tire?...

Title: Re: circujmference of rear tire.
Post by Rodger on 12/13/15 at 10:40:50

I'm sure Kris's math is correct, but for giggles, I'll do a roll-out check of both my tires. They're the OEM IRC tires with only 125 miles on them, so should be pretty accurate (heck, they still have most of their "rubber whisker," still).

Have to wait for snow to melt, but will post measurements as soon as I can.

Title: Re: circujmference of rear tire.
Post by Paladin. on 12/13/15 at 13:13:20

43425F40141F49482D0 wrote:

Didn't mean to start an argument.
By stock I mean an IRC 140/ 80- 15....

http://www.irc-tire.com/en/mc/products/cruiser/gs-18/
SIZE TYPE L.I. OVERALL DIAMETER
140/80-15 M/C TT 67H 612 (24.09" diameter, 75.7" circumference.)

Title: Re: circujmference of rear tire.
Post by Kris01 on 12/13/15 at 14:01:15

And there's an example of what "should be" and what "is"! IRC manufactures their tires (like everybody else) close to the specs that "should be". No one is ever exact. Chalk it up to manufacturing tolerances. That's why some brands of 140/90-15 fit without rubbing and some rub. ;)

Title: Re: circujmference of rear tire.
Post by norm92de on 12/13/15 at 15:01:20

I really miss a tachometer and would like to know the engine RPM at various speeds.
I have a GPS to measure speed so would then be able to check the speedometer and engine RPM by calculating the gearing.
I haven't taped the tire on the garage floor if I do It will be interesting to see how close theory and practice work out.
The tire has 1500 miles on it so far.

Thanks for the input.

Title: Re: circujmference of rear tire.
Post by Dave on 12/14/15 at 03:20:49

When I was setting up my Trail Tech Vapor.....I did the tape on the tire trick to establish a rolling distance. When I then programmed that into the speedometer and started checking mile markers along the highway, I had to make a correction. The rolling distance at speed and when your weight is on the tire - is not the same as when you are pushing the bike across the garage floor.

If you want to get a bit better accuracy - push the bike for 2,2,4,5 tire rotations....whatever you have room to do in your driveway.

For what you are doing....you might just look at Serowbot's gearing charts and find what you want to know.

5 speed chart:
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1341162964

4 speed chart:
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1341280735

Title: Re: circujmference of rear tire.
Post by norm92de on 12/14/15 at 08:03:46

Thanks Dave.
Those charts are all anybody needs. I needn't bother doing any of my own calculations.
The next best thing to a tach. ;D

Title: Re: circujmference of rear tire.
Post by Kris01 on 12/14/15 at 16:32:46

Tires also expand a bit at speed which essentially raises your gear ratio with the "taller" tire.