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Author Topic: Needed: Larger brain  (Read 849 times)

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Offline azuredesign

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Needed: Larger brain
« on: April 13, 2014, 08:39:59 am »
I have changed over to a 110/90 ×18 front tire on a 2.15 rim. Can anyone tell me what the difference in circumference is between this and a stock tire on a stock rim? I am trying to figure whether odometer and speedometer difference will be significant.
Thanks for any help!
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Offline LesterPiglet

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Re: Needed: Larger brain
« Reply #1 on: April 13, 2014, 09:00:57 am »
Going from 19 to 18 your speedo will read 56.8MPH at 60 MPH. 5% lower.

http://www.onlineconversion.com/bigger_tires.htm
« Last Edit: April 13, 2014, 09:02:47 am by LesterPiglet »
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Offline azuredesign

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Re: Needed: Larger brain
« Reply #2 on: April 13, 2014, 10:34:48 am »
Thanks for your thoughts and the link, but that is a gross approximation.
That was my inital thinking as well, but tire width, proportion of tire width to sidewall height, and rim width all figure in. I am simply not smart enough to come up with an accurate figure. I am thinking about simply inflating a stock tire on a stock wheel to the same setting, and measuring compared to the new 18" wheel, but I am not sure I can do so accurately.
« Last Edit: April 13, 2014, 10:36:27 am by azuredesign »
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Offline azuredesign

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Re: Needed: Larger brain
« Reply #3 on: April 13, 2014, 10:39:08 am »
Also, i would have thought with my slightly shrunken and softened 60 year old brain, that because a smaller wheel turns more times over a given distance than a larger one, that using a smaller wheel would show a greater, rather than lesser speed, and register more miles on the odometer?
« Last Edit: April 13, 2014, 10:41:00 am by azuredesign »
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Offline TwoTired

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Re: Needed: Larger brain
« Reply #4 on: April 13, 2014, 12:10:44 pm »
Quote from: azuredesign on April 13, 2014, 08:39:59 am
I have changed over to a 110/90 ×18 front tire on a 2.15 rim. Can anyone tell me what the difference in circumference is between this and a stock tire on a stock rim? I am trying to figure whether odometer and speedometer difference will be significant.
Thanks for any help!

What were your stock dimensions?

3.25x19?
Inch size tires were 95-100% aspect ratios.
So, (3.25" x 2) + 19"  yields a total diameter of 25.50" . The circumference of such a combo is C = Pid, or 25.5 X 3.14 = 80.07 inches traveled for one revolution of the tire.

90 % of 110 = 99mm  Convert to inches  = 3.9"  So, (3.9" x 2) + 18" yields a  total diameter of 25.8" .   25.8 x 3.14 = 81 inches traveled for one revolution of the tire.

Your speedometer would register lower speed, because the wheel turns less per distance traveled, and your odometer will record less miles traveled as it expects the wheel to turn more revs per mile.
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Offline azuredesign

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Re: Needed: Larger brain
« Reply #5 on: April 13, 2014, 02:08:22 pm »
First, thank you to both Twotired and Lester Piglet.

Second, is it possible to tell whether the crown of a new 3.25" a 1.85 rim is any more or less pronounced than a 4.33 " (110mm) in a 2.15 rim, thereby changing the circumference?

Third, funny how the smaller diameter wheel actually has a larger circumference as a result of the width of the tire, and tire aspect ratio!

Four, please help me clarify my fuzzy math, as I get a difference between the two circumference as a 1.15% difference between the two  circumference, and .124% difference in the difference in the number of turns each wheel makes over a mile(782.2 vs 791.3)

Are these differences significant given the accuracy of the stock speedometer and odometer?

Thanks again!
« Last Edit: April 13, 2014, 02:10:25 pm by azuredesign »
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Offline Don R

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Re: Needed: Larger brain
« Reply #6 on: April 13, 2014, 02:52:05 pm »
no.
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Offline Ricky_Racer

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Re: Needed: Larger brain
« Reply #7 on: April 13, 2014, 03:11:20 pm »
This tire calculator might come in handy... http://www.tacomaworld.com/forum/ Just click on "Tire Calculator" to find the circumference of the tire you're considering. RR
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Offline Retro Rocket

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Re: Needed: Larger brain
« Reply #8 on: April 13, 2014, 03:51:42 pm »
Seeings though the Honda speedo's are notoriously inaccurate, I would drive beside a modern bike or car and get a reading off their speedo, gps is even better....
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Offline BobbyR

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Re: Needed: Larger brain
« Reply #9 on: April 13, 2014, 04:01:52 pm »
Quote from: Retro Rocket on April 13, 2014, 03:51:42 pm
Seeings though the Honda speedo's are notoriously inaccurate, I would drive beside a modern bike or car and get a reading off their speedo, gps is even better....
Actually this is the bottom bottom line. This is no a precision instrument.  ;D ;D ;D ;D
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Offline azuredesign

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Re: Needed: Larger brain
« Reply #10 on: April 13, 2014, 04:28:50 pm »
Quote from: Don R on April 13, 2014, 02:52:05 pm
no.
[/quote

Thanks guys!

Like having one knob on a guitar, this was the one word answer I was looking for! Happy riding season to all!]
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