[Healeys] Incorrect Speedo Reading

[Bob Spidell]

Bruce,

You can get a pretty good approximation from a gearing calculator.  
Here's one:

http://www.angelfire.com/fl/procrastination/rear.html

Here's info on the speedo's innards:

http://home.comcast.net/~rhodes/speedo.html

You can 'calibrate' the speedo by repositioning the needle.   It'll be 
accurate only within a fairly narrow range; I usually shoot for accuracy 
around 60mph.

I got a new cable from Moss a while ago that helped the bouncing needle 
problem.

Bob



Bruce Griffin wrote:
> Gentlemen,
>
> This a very basic question, but I am hoping for some insight to see if there
> is a common Healey reason for this.
>
> I know my speedo has been bouncing, so I want to replace the cable to see if
> that helps.  My main question is how to estimate my speed based on my
> obviously incorrect speedo reading. I checked my speed with another car and
> knew it was off. Today, I passed a PD temp. speed camera that displays your
> speed. It indicated I was going 40mph, while my speedo showed my speed at
> 55mph. If I remember my engineering training from college, this is related to
> the gear in the transmission and I should be able to adjust my speed by using
> the fraction 40/55.  This assumes a portion for correction as opposed to a
> simple add 15mph because the gearing of the speedo drive gear is adjusted by a
> percentage, not a fixed number.  Any advice appreciated.
>
> This is also a good math problem for my 11yo son.
>
> Regards,
> Bruce D. Griffin
>
>   


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Bob Spidell           San Jose, CA            bspidell at comcast.net

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