[TR] TR3 Speedometer Calibration Graph

Mo and Dave MacKay m.d.mackay at sympatico.ca
Thu Apr 11 15:22:40 MDT 2013

Bob Danielson has an excellent write-up on his web site:

I created a little spreadsheet that calculates the speed at any rpm in a
particular gear when I was contemplating installing the HVDA conversion in
my TR3A.  I'd be happy to send it to anyone on the list who might find it

After installing the HVDA transmission, I found myself routinely speeding so
that I figured I'd better re-calibrate my speedometer. I sent my speedometer
to Margaret Lawrence at Mo-Ma in New Mexico. She charged US$150 to
recalibrate the speedo and had it back to me in about 2 weeks. I'm happy
with the work that Mo-Ma did.

In order to calibrate the speedo, Mo-Ma needed to know how many revolutions
the speedo cable makes in a mile. My speedo was set for 1184 revs per mile.
To determine what the revs are now, I measured out 59 9= (1/100 of a mile)
on the road in front of my house. I marked the wheel and pushed the car over
that distance to see how many revs the cable made. I repeated that 4 or 5
times. I came up with 10 complete turns and a partial turn of about 215
degrees, which works out to 10.5972 speedometer cable turns over the 52 9=
distance. Consequently, I asked Mo-Ma to calibrate my speedo for 1060 revs.


Dave MacKay

1960 Triumph TR3A
s/n 68639L
near Toronto, Canada

>Message: 7
>Date: Thu, 11 Apr 2013 08:05:13 -0700 (PDT)
>From: William Brewer <wsb1960tr3a at att.net>
>To: Triumphs <triumphs at autox.team.net>
>Subject: [TR] TR3 Speedometer Calibration Graph
>Message-ID: 	<1365692713.60557.YahooMailNeo at web180904.mail.ne1.yahoo.com>
>Content-Type: text/plain; charset="us-ascii"
>     Is there an online pdf for the calibration for a TR3A speedometer with
>overdrive? I would like to do a check of rpm's verses speed indication.
 >    Bill in Tehachapi

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