[Mg-t] TC speedo in a TD

[Bob Donahue]

   I found a web page that said the TC speedo is S461-1675 and the TD is
S561-1600. http://ttypes.org/ttt2/mg-tc-dash-instruments The page says the
second number is the "cable turns per mile". To me, the extra 75 turns of
the TC speedo means the miles and speed will read low by 4.7% in a TD. This
is not a horrible error in my opinion. Heck, my B reads 5% high with the
correct speedometer.

I will take my GPS for a little ride and find out what the real error is. 
With the cost of these instruments, I can put up with a small error.

Bob Donahue (Still Stuck in the '50s)
Email - bobmgtd at comcast.net
Cars:       52 MGTD - #17639
               71 MGB - #GHN5UB254361
Member:  NEMGTR #11470
               NAMGBR # 7-3336
               Hoosier MGB Club
               Olde Octagons of Indiana

----- Original Message ----- 
From: <mgbob at juno.com>
To: <bobmgtd at comcast.net>
Cc: <mg-t at autox.team.net>
Sent: Sunday, August 05, 2012 4:34 PM
Subject: Re: [Mg-t] TC speedo in a TD



Hi Bob,
  I make the assumption that 1675 is turns of the cable per mile.
  You can probably do the maths to solve for speed with variables of 
wheel&tire diameter, or circumference, and gear ratios, etc, but I think 
that it would be more practical to run a measured mile or to use a GPS.
  I have the formula somewhere for wheel&tire circumference, gear ratios, 
etc. let me know if you would like to try it.
  Oh, another factor--on the TDs  and TFs where we have used the formula, we 
found the speedos were all a bit faster than calculated. Perhaps a bit of 
Safety Faster....
Bob
---------- Original Message ----------
From: "Bob Donahue" <bobmgtd at comcast.net>
To: "mg-t" <mg-t at autox.team.net>
Subject: [Mg-t] TC speedo in a TD
Date: Sun, 5 Aug 2012 15:04:06 -0400

I just discovered that the Jaeger speedometer in my TD came from a TC. The
number is "S461 1675". Can anyone tell me what the error in speed and miles
is?

Bob Donahue (Still Stuck in the '50s)
Email - bobmgtd at comcast.net
Cars:       52 MGTD - #17639
               71 MGB - #GHN5UB254361
Member:  NEMGTR #11470
               NAMGBR # 7-3336
               Hoosier MGB Club
               Olde Octagons of Indiana