There are several factors that are likely to be involved in your
finding that the speedo and odo are reading high.
Road & Track's 1953 test report for the MkII TD noted that the MG
speedo read 60 while the R&T speedo read 55.9.
The original Gold Seal tire circumference was 83.9 inches. Michelin &
Kleber 165 x 15s that I measured were 77.93 inches. The 155
circumference may be smaller still. Better than estimating tire sizes is
to wrap them with a string, then measure it.
50 year-old instruments may be showing their age.
TD & TF axles were interchangeable, as were their gears. MG offered
three sets of gears for the TD, 5.125, 4.875 and 4.55. I don't know what
was offered for the TF, though we do know that 5.125 was standard TD
ratio and the MkII and TF cars had 4.875 standard ratios.
These made sense for the UK fifty years ago. For use on our roads
today they are less than ideal. Carl Cedarstrand wrote a manual for gear
swapping, available from Moss, in which he discusses ratios and changing
gears to alter them for today's needs. To summarise, he wrote that most
TD owners seemed to be happy with the 4.3 gears from MGA, though some
liked the taller 4.1 gears.
A couple of years ago, someone wrote an article for TSO that described
the use of a $25 bicycle speedometer, operated by a magnet taped to a
wheel that passed the sensor fastened to steering arm, that not only was
ideally cheap but quite accurate. For a quick fix for more accurate
rallye driving, that would be something to try. One Mini owner in our
club did it this summer and is most pleased with it. He recommends
Wal-Mart's bicycle section.
I worked up a table of gear ratios and some tire sizes, with MPH/1000
rpm, RPm@60 mph, MPH@3500 rpm, MPH@3750 rpm, and MPH @2500 ft/min piston
speed. If you would like a copy, send me your snail mail address.
Bob
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