Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Speedometer Calibration

You certainly can 👍
I just bodged it😆

Hello Planenut, I have a question about the number we have to enter in our speedo while in configuration mode.

The instruction say that, if we have Avon standard tyres, the number should be set to 004060.

And with, for example, the taller Blockleys it's 004045 (a lower number). And with the Michelin Commander II, it's 004400, even smaller.

The smaller the tyre, the bigger the number...

What do these numbers mean exactly? What are they related to?

When I set up my speedo on my mountain bike, the number I have to enter is the outer diameter of the tyre, fully inflated. So the bigger the tyre, the bigger the diameter so bigger the number you enter in the speedo.

So, I can't find the relationship with the numbers you indicate and the radius or the diameter of the tyre. Maybe it's because of the units o something? I'm just curious, but as I'll probably do very son this re-calibration on my brand new M3W, I would love to know the origin of the numbers I enter

Good bodge👍

Not 100% sure but I think it relates to the number of pulses (revolutions of the wheel). The standard setting is 3795 that relates to a very big diameter tyre that doesn't exist in M3W terms, hence the error. The new Blockleys are a little larger in diameter than the used Avons, so a smaller number. New Michelin Commander II are smaller diameter and they must rotate more times over the calibration distance, so a bigger number (not smaller as you say). There is also a calibration feature that you can use over a known distance of a mile (or maybe a km?). I have not done a metric speedo but I assume the same system applies.

This makes sense. The bigger the diameter, fewer the turns - so the number - to make the same distance.

About the Michelin Commander II, as you pointed out I made the mistake to write it otherwise. Totally correct. Sorry for the confusion.

If we know the outer diameter of any of these tyres we can calculate the distance this number is referred to. Has anyone the outer diameter of the Avons or the Bockleys? Just for curiosity.

What’s clear is that this is something to be done. I mean the calibration. Not Only to be sure the real speed we drive at, but also because the mileage as the speedo is set from Factory is false by at least the 6%. Nothing to scream about, but the more realistic the better.

Thanks Planenut for the instructions. I will do it as soon as possible. I hope to find the calibration plug easy, but I guess it won't be... as my M3W has heated seats.

I bet this plug is still there on our new 3-Wheelers. If not, why wiring the speedo? I mean: Obie found out the Black and Grey wire coming out the speedo's plug. So it has to end somewhere...

Exactly my thoughts Javier it must be somewhere, let us know if you find it.

I know that you could do the calculations but as the alteration of the numbers is quite easy to do, once the plug is located, I found a bit of trial and error against a sat nav was close enough. It is certainly much better than before. As mentioned, there is also a calibration mode you can do by driving over a known 1 mile distance. I notice that the link at the start of this thread still works.

Pulled off the bulkhead to look for the elusive black and gray wire coming out of the speedometer.
Found it coming out of the plug on the speedometer, but it disappears into a wire loom, never to emerge.
I took a wire and soldering a fine pin to it. I inserted this into the back of the speedometer plug where the black and gray wire emerges.

Used this set up to run the calibration, that way I did not have to cut into the wire.

I can't find the magic connector in my 3W, but looking behind the fuse box I do see a a gray and black wire in a bundle marked "Morgan Panel Harness". It seems a likely candidate, but I thought I would post it here and see if anyone disagrees with me before I start cutting. Thoughts?
Marked with a red arrow in the picture. If this does work it may be clue for others to follow.