Author Topic: calculating mph from tire circumference?  (Read 10404 times)

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Offline entropy

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Re: calculating mph from tire circumference?
« Reply #15 on: August 20, 2014, 06:37:17 AM »
Sumner,
The "slip" adjustment is not critical at all, we just want to go to WOS with appropriate alternative gearing in case our current 2.19 proves to long to achieve 175-200 at the Q.  I am not trying to "mic a brick", just looking for directional info which has been generously provided by all you guys.   My big AH-HA was tq converor slip; you and Tom both pointed in that direction last night.
 :cheers:

As far as crossing the Q at the speed needed for each license we plan to use the GPS display on the dash. 
If that is too hard to see, i'll set up a warning light triggered by the GPS speed.  Racepak warning lights are impossible to miss, even for me.
Karl

Offline entropy

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Re: calculating mph from tire circumference?
« Reply #16 on: August 20, 2014, 06:42:07 AM »
I have, and still do, used Karls corrected spreadsheet for years and it is spot on!!
:cheers: :cheers: :cheers: :cheers: :cheers:

Offline Stainless1

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Re: calculating mph from tire circumference?
« Reply #17 on: August 20, 2014, 10:10:27 AM »
Karl, looks like your alternative 256 gear would still have you above 175 at 5800... if you have an alternative gear set I would bring them...
As a thought, 26 in tall tires would give you a 244 gear, and probably be easier to change unless you have a quick change.
When we change to a class that we need to long course qualify in, we always initially gear for the quarter number. 
Of course you may be over worrying, I suspect you will both be able to A license at the meet  :cheers:
Stainless
Red Hat 228.039, 2001, 65ci, Bockscar Lakester #1000 with a little N2O

Offline entropy

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Re: calculating mph from tire circumference?
« Reply #18 on: August 20, 2014, 01:27:14 PM »
Karl, looks like your alternative 256 gear would still have you above 175 at 5800... if you have an alternative gear set I would bring them...
As a thought, 26 in tall tires would give you a 244 gear, and probably be easier to change unless you have a quick change.
When we change to a class that we need to long course qualify in, we always initially gear for the quarter number. 
Of course you may be over worrying, I suspect you will both be able to A license at the meet  :cheers:

Stainless,
we do have a Winters quick change
(But we do hope we don't need to get into it  :-D)
Karl

Offline fredvance

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Re: calculating mph from tire circumference?
« Reply #19 on: August 20, 2014, 03:15:44 PM »
Is it harder than changing gears on a Busa?? :evil: :cheers:
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Offline entropy

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Re: calculating mph from tire circumference?
« Reply #20 on: September 24, 2014, 08:43:59 AM »
"I'd rather be lucky than smart" = karl's slogan

After plenty of discussion, TFA went to the recent WOS using a 6.0% "slippage" factor to predict mph & select gearing.
I determined that factor at 2012 WOS for my bike.

2.19 overall gearing, 6% "slip"  @ 91.25" tire  @ 5722rpm = 212.2mph predicted

results please...drum roll...                                 5722rpm  = 209.6mph measured(GPS) = 7.2% "slip"

pure luck that the prediction turned out to be so close, i wasn't thinking at all about our car's tq convertor...

Offline WOODY@DDLLC

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Re: calculating mph from tire circumference?
« Reply #21 on: September 24, 2014, 09:10:12 AM »
The difference is obviously entropy!  :-D :-D :-D
All models are wrong, but some are useful! G.E. Box (1967) www.designdreams.biz

Offline entropy

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Re: calculating mph from tire circumference?
« Reply #22 on: September 24, 2014, 09:50:15 AM »
The difference is obviously entropy!  :-D :-D :-D

LOLOLOLOLOLOLOLOLOLOL :cheers: