Steve---You are right about the tires giving you the 5% difference, if
this car came with 165's from the factory. I don't know if these
speedos go out of calibration or not, nor do I know why the tach is
"off" by 500 rpm. (At what road speeds)? The tach should read 3,000
when traveling at 62 mph in fourth gear.
To confirm that your speedo is in error, there is a test that one can
do.
Down in the bottom corner of the speedo face is a four digit number.
(Mine happens to be "1120".) This means that all such speedo cables
should turn 1120 times when traveling one mile. It then means that the
cable should turn 11.2 full turns when traveling 1/100 of a mile, or 52
feet, 9.5 inches. By disconnecting the end of the cable and having it
down where you can observe the revolutions, and count the turns. First
mark off the distance on the pavement. The difference between what you
count, and the number painted on your speedo is the error.
By reporting the difference, speedo repair shops can recalibrate to get
it exact, using the tires, and presumably, the differential gears you
want to keep.
Dick
From:
lindquistse@charter.net(Steve Lindquist) Date: Yesterday I had my
daughter drive behind me on a stretch of interstate to check my
speedometer. At 70mph indicated on the TR she reported just over 62 on
her car. I also have a tach that reads high by approximately 500 rpm, no
overdrive and tires that are 185SR15 on my TR250. That would make the
circumference about 5% greater than original, which should make me
faster than indicated, not slower. Do these instruments go out of cal,
or is it more likely cable issues or ..?
Steve Lindquist
508.869.6709
lindquistse@charter.net
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