speedo accuracy

[Rabbit16v@attbi.com (Rabbit16v)]

Your only fault in all of this is that you haven't had it radar checked.
I'll bet if you did have it checked with radar that it would be off just
like everyone else's.  I guess the problem that we need to figure out is
where our calculations are going wrong.  At this point I think we need to
question the charts we have access to on the internet?  Anyone have a chart
on paper in a manual or something that they can compare to the charts on
Scirocco.org?

Dave

>
> My $.02 CDN on the speedo issue (along the same lines as Ron's)  Both the
> Scirocco and the winter-beater Jetta have 7A transmissions in them.  The
> Scirocco has the stock 220KM/h speedo, and the tach is a W-field
> alternator driven unit from an 89 Jetta TD (ranging from 0-5000rpm)  The
> Jetta has a 16V speedo (260km/h) and tach (0-8000rpm)  The speedo drive
> gear matches the R&P of the transaxle (3.94 in the 7A)
>
> These two cars read as dead on as I can reckon by eye for RPM vs.
> indicated speed on the speedometer - ie. 100KM on the clock is 2575 rpm on
> both tachs (admittedly harder to pinpoint on the 8K tach due to scale...)
> which impresses me, especially as the Scirocco's tach runs from the pulses
> on the alternator, not the ignition, which means it's more prone to error
> (belt slip, different pulley diameters etc)
>
> I know that the Scirocco's actually speed will be off very slightly
> (compared to the indicated speed) because it has 185/60R14, which results
> in a slight increase in travelled speed (the rpm difference at 100km/h is
> less than 50 though)
>
> Personally I'm impressed by the consistency of VW's speedos, even if they
> are optomistic (which I have not had occasion to determine.)  The fact
> that these two cars with different tachs and speedos come up with the same
> readings as can be calculated from gear ratio and tire diameter is cool.
>
> Drew
>
>
>
>
>
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