Evening All,

As I sit here worrying about what could go wrong on my SVA test yet another thought occured to me.
I have set the dip switches on my Greengauges speedo using the calibration number in the Greengauges data sheet ie 3562. If it turns out that my speedo is underreading and the nice SVA man will let me correct the speedo do I need to increase or decrease the calibration number. Hope someone with Greengauge instruments can help as I can't get my head round this one.

Regards

David

Now, I am not sure what the calibration number is, but it sounds like a circumference of the wheel in mm to me.

If so, then if its underreading it means the wheel is making less rotations per unit time to cover a given distance than it should be, and so the computer thinks the wheel is bigger than it actually is.

Logic then suggests that reducing the figure (assuming it actually is the circumference) will increase the reading on the speedo as it will think the wheel is smaller, therefore has to make more revolutions per unit time to cover the same distance.

Hope that makes sense and that I have got it the right way around. Or I will look an even bigger fool...

David

[Edited on 13/2/06 by flak monkey]

im not sure about your gauges, but my revotec number is diff ratio x no. of magnets x no. of revs per mile that the tyre does.


My numbers are

3.92 x 4 x 868.5027 = 13618

hope that might be some help

Tom

I set my Greengauges speedo according to the instructions and the SVA man said it was spot on.

Where are your magnets?

p.s. the calibration number is revs per mile. Increasing the number will lower your speedo reading.

Andy,

I used the circumference calculator on the "Tyre Bible" web site which gave me a circumference for a 195x50x15 tyre as 70.84". I then divided this figure into the number of inches in a mile 63360 and multiplies by 4 since I have 4 magnets on my drive shaft. The figure was 3557 so I used the nearest figure in the Greengauges calibration table which was 3562. Does my calculation seem correct?

Regards

David

Can't be bothered to check the calcs but if your calc is correct and it's revs per mile then you may be slightly under-reading by using that value....but probably not by enough for Mr SVA to pick up on...

OK....doing the maths....

Circumference is ((((19.5 / 2.54) * 0.5 * 2) + 15) / 2) * PI * 2 = 71.24 inches (I'm sure the tyre bible takes squishiness into account which would explain the lower value it gives)


So answer is ((1 mile) / (71.24 inches)) * 4 = 3 557

PS Links show the use of google calculator...

[Edited on 14/2/06 by stevebubs]

Sorry it's pulses per mile. Would be revs per mile with only one magnet.