I still don't get it!
What do the tires have to do with the ratio of engine RPM and
the speedo? The drive for the speedo is taken off of the back
end of the transmission. You could remove the back wheels,
back axels, the diff., and the drive shaft. Jack the car up and run
the engine and put the car in gear and the speedo would tell you
the ratio between engine RPM and drive shaft RPM.
I just don't get the bit with the size of tires.
>From: levilevi@home.com
>Hi Jim and others who replied RE: OD RPM/MPH
>
>On further review (it is Sunday after all) and after using the Dan
>Masters formula's (now on his website).
>
>I calculated that with my tires 205/70/15 I should have been reading
>77.36 MPH at 3000 RPM in overdrive (4th). And that Jim should have been
>going at about 71.6 MPH at 2800 in overdrive (4th) assuming he is
>running stock 185/75/15 tires.
>
>So Jim's gages are pretty close and my gages are pretty close (in my
>case just the 2 MPH difference due to the tires). It was my math that
>wasn't so good especially when I'm doing long division in my head doing
>77.36 MPH down the road. And probably my timing between mile markers
>wasn't so accurate either (a 0.5 second error means about a 1 MPH
>error).
>
>So Thank You to everyone who offered their numbers.
>
>Bud Rolofson
Brian
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Brian Borgstede I
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