[Shotimes] Speedo Error... was: My MPG Test is Working!!

[krazgeo@comcast.net]

 -------------- Original message ----------------------
From: Ron Childs <rbchilds@pacbell.net>
> Using bigger tires is the equivalent of using a numerically lower final drive 
> ratio or a higher gear. You get better gas mileage by driving 60 in 5th instead 
> of 3rd. The increased throttle opening required with the bigger tires does not 
> use as much air/fuel as the higher rpms of using a lower gear (or final drive 
> ratio) would.
>    
>   Am I clear as mud?

That is the exact logic I was using.  The car had too many revs at cruise, and a whole lot more torque than it needed, since it was geared wrong at the factory, for some reason.  I gave myself a higher overdrive by putting on the larger size.  I theoretically lose a bit of acceleration, both off the line and at the initiation of each gear during normal upshifting.  But the car still has plenty of power for those times....the excess capability was just being wasted.

All of this is knowledge learned in preparation for working on 'gearing up' the truck next year.  I'll have to go to a supplemental transmission to do the job with it...I want to slow the engine by 33% at cruise, from 3000 rpm to 2000.  I want to try to increase its mileage from 10 to 15.  New ones can do it...why not mine?

It's a 460 CID V-8...plenty of torque at 2000 to carry itself just fine.

George