Author Topic: Q on circumference of Front Runners?  (Read 5906 times)

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Offline jdincau

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Re: Q on circumference of Front Runners?
« Reply #15 on: May 09, 2014, 01:51:14 PM »
Just a data point.
Goodyear 808-029-090
25.0 x 4.5 x 15

D2209, made in Chile in 2002
LF, 6' 6 1/4", 78.25 roll out, 24.907 Dia.
RF, 6' 5 7/8", 77.875 roll out, 24.788 Dia.

D2284, made in USA in 2010
LR, 6' 6 3/8", 78.375 roll out, 24.947 Dia.
RR, 6' 6 1/2", 78.5 roll out, 24.987 Dia.

Just measured them +/- 1/16" at 60 PSI.
Unless it's crazy, ambitious and delusional, it's not worth our time!

Offline entropy

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Re: Q on circumference of Front Runners?
« Reply #16 on: May 10, 2014, 06:15:12 AM »
Thanks guys!

Some interesting variations, good data.

When i was running my Hayabusas, i kept very detailed info on tire circumference, ticket trap speed, logged trap speed, logged rpm and nearly always could correlate rpm to speed by less than 1/2mph.  

What was interesting is that on asphalt i needed to take 3.8-4.2% off the measured tire circumference to get the calculated speed = trapped speed.  In 2012 World Of Speed was very damp and we didn't get enough passes to develop a solid correlation
(although we did get enough passes to set MPS-F 1650 record... :-o)

Clutch was a lockup, so no clutch slippage.  
Prob tire slippage, but definitely not spinning or it would show up in rpm variations.

I'm guessing that car tires will need a similar "adjustment" in the calculations.
The tire circumference variations are very interesting, but in the end, I will find out what the "adjustment factor" is and calibrate my data accordingly.
karl


« Last Edit: May 10, 2014, 06:20:32 AM by entropy »

Offline sabat

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Re: Q on circumference of Front Runners?
« Reply #17 on: May 10, 2014, 07:57:41 AM »
Karl, how much did Greenie's rear tire grow at speed?

Do LSR tire manufacturers list a growth factor?

Dean

 :cheers:

Offline entropy

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Re: Q on circumference of Front Runners?
« Reply #18 on: May 10, 2014, 08:24:33 AM »
Karl, how much did Greenie's rear tire grow at speed?
Do LSR tire manufacturers list a growth factor?
Dean
 :cheers:

Dean, that's the weird thing, i have seen many times tire incr in diameter on the dyno.

But my correction factor is negative, the opposite direction of tire growth.  I have to give it LESS circumference (than i measure on the tire) to get the calculations to match trap speed at a specific rpm.
go figure

Offline sabat

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Re: Q on circumference of Front Runners?
« Reply #19 on: May 10, 2014, 09:10:01 AM »
Maybe holding front end on the dyno allows the bike to unload the tire, and on the track the weight transfer compresses the tire? Interacts with wheelbase, swingarm angle?

I'm setting up greenie with a hard tail and about 7/8ths clearance to the subframe, hopefully it will be enough.

Offline manta22

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Re: Q on circumference of Front Runners?
« Reply #20 on: May 10, 2014, 04:10:23 PM »
What is important is the "rolling radius" of the tire. This includes the compression of the tire due to load and is usually quoted at a given inflation air pressure. Race tire catalogs also frequently show the revolutions per mile. This is based on the tire's rolling radius.

A radial tire exhibits much less growth at speed than a bias-ply tire. Good luck on finding specs for this parameter.  :x

Regards, Neil  Tucson, AZ
Regards, Neil  Tucson, AZ