You're absolutely right, tire size won't affect speedo reading. But it will
affect actual speed. In my book I want to know both so that I know that the
reading on the speedo is what it should be and the difference between that
and actual speed for when Johnnie Law wants to pull me over.
Jim Altman jaltman@altlaw.com Illigitimi non Carborundum
http://www.altlaw.com/metro/jaltman.html 69-TR6#CC28754L(O) W4UCK
-----Original Message-----
From: owner-triumphs@autox.team.net
[mailto:owner-triumphs@autox.team.net]On Behalf Of Brian Borgstede
Sent: Monday, October 04, 1999 11:01 AM
To: triumphs@autox.team.net
Subject: Re: Excuse my o/d gloat
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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NEW E-MAIL ADDRESS: borgstede@umsl.edu
Brian Borgstede I
Telecommunications Engineer, I '68 Triumph
University of Missouri, St. Louis I
Instructional Technology Center I TR-250
Phone: (314) 516-6433 I (or 2 or more)
Fax: (314) 516-5294 I
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