Tue Jun 24 12:57:27 1997 - Message No. 1091
From: "Robert Rowe"

Subject: Re: Tripmaster


Juergen Reimann and Stefan Loth have raised the subject of Speedo vs
Tripmaster accuracy.

As I understand it, the manufacturers have to make the speedo optimistic

as a mater of law and self protection.

I believe in the UK, the speedo must over read by 10% at 30mph, so to to

really travel at 30mph, you should have 33mph registering on the speedo.

Though there is no requirement to continue this practise byond 30mph, in

reality, the manufacturers tend to do so. One car magazine I read
recently had tried speedos at an indicated 70mph and found them all to
be optimistic, some, notably Mr Ford's being even more so than others.

On the STOC list, the question of speedo accuracy was addressed and
research carried out, and speedo accuracy was found to vary across the
speed range. The range of variation being between 5 and 10%.

Whilst this study was conducted in the US, an approach to the
manufactuers via a magazine on this subject with the results gathered,
got the response, "Our lawyers suggest that we do it that way".

Personally, I think there is a cost element in it and that rather than
say it can be done, but do you want to pay for it, the manufacturer,
knowing what the answer will be is hiding behind its lawyers.

The cost of building a speed measuring system that is accurate to levels

some people would like would be very expensive and considerably more
complex than the current setup which is prone to errors created by
changes in the size of tyres, amongest others.

Whether you really do need a more accurate speedo is also open to
question as if you need that sort of accuracy, you can easily get it by
going and getting GPS.

Yours

Rob



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