Joe,
It's very rare that I disagree with you (in fact, I don't think I ever have),
and I'm not sure if I'm disagreeing in this case, or just misunderstanding you.
If you change your tyres, then, at a given engine speed and in a given gear,
your road speed will change (faster for bigger tyres, slower for smaller tyres).
However, the speed shown on your speedo will *not* change (i.e. it will be
wrong). Therefore, I disagree with the sentence below, "changing the tyre
diameter will vary the speedometer reading" - it will *not* vary the speedometer
reading if the engine speed and gear selection are the same; it will, however,
vary the actual road speed.
If this is what you meant, then hopefully I've cleared things up a little bit,
because this is not how I read your e-mail.
If you really did mean that at the same engine speed, the speedo will read a
different value depending on tyre size (and diff ratio) then could you please
explain how this is the case, because it is not my understanding?
Cheers,
Dean
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Date: Tue, 23 May 2000 07:01:59 -0700
From: Joe Curry <spitlist@gte.net>
Subject: Re: speedos and rotating diameter
Let me weigh in on this one.
There is definately a difference in the tach to speed ratio if everything else s
not equal. Changing tire diameter will vary the
speedometer reading , as any tire shop will tell you. Also varying the ratio of
the differential will change the speedometer reading.
While you can calculate the speed by doing the proper math, all the elements
must be taken into consideration. the drive line does not
end at the back of the transmission where the speedometer cable is connected.
Joe
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