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Re: Speedo question HELP
Quote:
Originally Posted by TBONE1964
The factory tachs are wired to the ignition coil and read engine RPM only. The trans, gear ratio and/or tire size will have no effect on the actual tach reading.
However, if you for example run 65 mph and your tach shows 3000 RPM and you changed your tire from a 255/70 15 to a 235/70 R15 then your tach would read a different RPM at the same 65 mph.
It is possible that you tach is out of calibration. Have you checked it against a timing light?
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I hear what you are saying and its funny you picked those two tire sizes because I used to have 235/70 15's on the truck and now have 255/70's and the tach is out the same amount with both tire sizes. Could it be the tach is pooched or because the factory tach is hooked to a HEI which it was when I bought the truck.
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