Subject: [Fot] Rear End Ratios

From: "john hasty" <[email-masked]>
Date: Mon, 1 Jul 2013 12:57:02 -0400

The overall ratio we have in the TR3A is 3.7 achieved with a 4.1 rear end
and overdrive.  At VIR, Road Atlanta, Savanna and Mid Ohio, all with long
straights, we are turning 6200 at the end of each of them.  Elkhart Lake has
longer straights and we are concerned that we might need a taller rear end
gear.  If we put 3.7 rear end gears in we would have an overall ratio of
3.66 which I believe would produce 800rpm less or the same as turning
7000rpm with the 4.1. I can't turn 7000 with a stock crank so;   Does anyone
with experience at Elkhart have a suggestion?   What do you run there?
Thanks guys/gals......

John H. Hasty
Attorney At Law
Guthrie, Davis, Henderson & Staton, P.L.L.C.
719 East Boulevard
Charlotte, North Carolina 28203-5113
Tele: (704) 372-5600
Fax: (704) 372-4601
E-mail: [email-masked]
www.gdhs.com
 
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From: "Randall" <[email-masked]>
Date: Thu, 4 Jul 2013 17:00:54 -0700

> This issue relates to the bearing in the epicyclic gear 
> (around which the three planet gears spin) - which therefore 
> runs at three times engine speed.

Nope.  Since the entire overdrive is driven from the output shaft of the
main gearbox, it's speed is relative to that.  Meaning it all turns some 3
times slower in 1st gear than in 4th (for a given engine rpm).

And the gear that the three planet gears turn around (which most of us call
the 'sun' gear) is either stopped relative to the shaft it runs on (direct
drive), or is stopped relative to the housing (with the shaft turning at
input rpm).  Nothing runs at 3 times shaft rpm.

-- Randall