RE: Spedo/Emissions test on 2-wheel dynamometer

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

I wouldn't worry about this practice causing damage to the drivetrain ... as
long as the rear wheels stay off the ground!  :-)

The speedo really just measures the speed of the left front wheel (the
sensor is in the transaxle and samples the shaft that hooks up to that drive
flange.  As long as the center diff was locked the readings should be OK
though.  It is a bit of a non-sequitur that one would read high and the
other low, because both measurements were based on the speed given the
effect of the tires.  Both numbers are pretty doggone close to correct
though, and I wonder how accurate you expect the speedo to be?  Given that
the "flying 5 mile" test requires extremely close control of the vehicle
speed, I'd say that I'd trust the dyno number most.  

HTH!
Steve Buchholz
San Jose, CA (USA)

> -----Original Message-----
> 
> A local speedometer  shop jacked the rear-end of my 4kq and 
> had to lock the
> center differential to test my speedometer with the front 
> wheels on rollers.
> 
> Is this method of testing damaging to the drivetrain?
> 
> Using the roadside speedometer check signs (timing over a 
> distance of 5
> miles with speedo reading 60 mph), my speedometer reads 
> approx. 3mph more
> than actual speed.  By shop-dyno test my speedometer reads 
> 1mph less than
> actual speed. (both at 60mph)
> 
> Why the difference?  Which is more accurate?
> Does the speedometer on the 4kq correlate with the front 
> wheel speeds, rear
> wheels, or does the Quattro system allow different front and 
> rear wheel
> speeds (even with center differential locked) which would 
> make the front or
> rear wheel speed inaccurate?
> 
> Thanks in advance.
> Chuck
> Seattle, WA
>