Speeding?

[phil.borden]

Recently I had the chance to borrow a Road Angel, primarily to check my speedo. To my amazement things where not exactly right. It became apparent why I seemed to be overtaking the majority or vehicles on my regular trip on the A1(M). Thinking I was safe sitting at an indicated 80mph I was actually doing 93!

This, even having passed the SVA after the tester allowing a couple of iterations to adjust the pulse count.

Using the GPS calculated speed I have now got an accurate speedo and I am now also a bit happier about by gearing as it did seem to be a little short.

Has anyone else had similar experiences? It just goes to show it may be worth doing an independent check if you can.

[davefiddes]

I've had a few issues with the speedo calibration. Checking the speedo with a GPS is definitely a good idea. I actually found that the values for the pulse count per mile listed in the manual were spot on with my Goodyear rears. I've since reduced the ppm figure by a few percent to over-read a bit.

If you find that the Ultima supplied numbers are significantly different and you are running Goodyears then you may want to have another look at the speedo sender unit. The orientation and the gap between the cutter plate and pickup are both critical. The pickup should be absolutely central and aligned with the cutter plate and the gap should be no more than 1mm (mine runs 0.5mm with a tiny amount of variation as the driveshaft rotates).

[YIIHAA]

You may get the speedo reading correctly, but never the odo at the time. (assuming you are using the factory VDO instruments)

[phil.borden]

I sourced my Tacho and Speedo from ETB Instruments rather than Ultima, although I suspect they have OEM internals (ie are VDO).
With an electronic speedo I would hope, providing the face is marked correctly, that setting a pulse count per mile calibration will mean that the speed reading is correct and also that it is able to count miles (afterall, all it has to do is maintain a running count of pulses and divide by the number per mile). However, I think the Road Angel has a distance function so I will check my ODO reading against the GPS distance and see what happens.

[YIIHAA]

phil.borden said:

providing the face is marked correctly

Exactly.

See if you can find a speedo with a full scale deflection of 200mph here:

VDO Cockpit vision Speedos

Makes you think that your fuel economy is 30% worse than it actually is

[BobM]

YIIHAA said:

You may get the speedo reading correctly, but never the odo at the time. (assuming you are using the factory VDO instruments)

I'm pretty confident my odo is about right. I calibrated the speedo using the Road Angel and the odo seems pretty much spot on over 'known' and fairly long routes.

Wonder if this could be due to the sender unit not being set up quite right and therefore losing some pulses while still showing accurate speed due to using pulse to pulse interval and ignoring longer than average intervals?