teseract@moparhowto.com writes:: >>
I've read in the archives that trucks with the 3.90 rear end with the
stock tires (which are a good 3" shorter in diameter than my 31" tires) pull
about 2000rpm at 60mph. This seems odd to me as the underhood sticker
doesn't
indicate anything about the different gear ratio - but if I had the standard
3.22 gears I don't think I'd be pulling the RPM I'm pulling at 60mph with
the
size of tires I have. <<
The different tires will not make a difference in the reading of the
speedo @ any given RPM .. You have changed the effective
gear ratio, but the rpm of the tailshaft is still the same as it was
before in respect to the engine RPMs.(direct connection in high
gear with the torque converter locked up). The tires are longer in
circumference, so you are actually moving farther(faster) @ a
given with taller tires, but you have to change the driven gear in
the tranny for the speedo to correct the rpms indicated @ any
given speed.. The driveshaft is turning fewer turns to get the
same distance, therefore the reason for having to make an equal
correction to the drive gear for the speedo(located on the end of
the speedo cable where it enters the tranny)..
Anytime the tires are changed to a tire with a significant
difference in circumference the speedo will not read correctly
unless it has been "recalibrated" or corrected.
There are aftermarket devices on the market that you can purchase
that are adjustable for this type situation, but I have no experience
with them..
Since the '95 went to electric speedo(I think) none of this may
be relevant.. It worked on the mechanical speedos.
We could certainly slow the aging process
down if it had to work its way through Congress.
- Will Rogers
Azie
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