Got my acewell digi speedo today , can any one please tell me what setting i need to put in it to set the circumference so the speedo works acurate.

I am running on 185 70 13 tyres and thinking of mounting the sensor on the prop

Many thanks

Davrus

The props going round around 3-4 times faster than the wheels. (You need to find out what your diff ratio is exactly).

Measure the circumference of your wheel + tyre either with a tape measure or chalk marks on the tyre wall transferred to the ground.

Then you need to divide your circumference by the diff ratio so it counts correctly. (Assuming my logic circuits are working today. )

David

how do i find out the ratio

The most accurate way is to look inside the diff at the crown wheel. It'll have the ratio painted on it. Or count the teeth on the crown wheel and pinion.

Guess it then when you go for sva, take a calculator.
If the sva man says it is 5% too fast, just take the wheel measurement that you inputed and reduce it by 5 %.
Do you get the idea?
He will allow you to alter the settings and retest.

185 70 13 tyre should be 1851mm circumference, and should turn 540 revs per km or 869 revs per mile. so if you want to mount your pick up on the propshaft you need to divide 1851 mm by your diff ratio. ie 1851 divided by 3.62(sierra) equals 511.325mm. i think

[Edited on 4/11/06 by martthefridgeman]

quote:

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Originally posted by martthefridgeman
185 70 13 tyre should be 1851mm circumference, and should turn 540 revs per km or 869 revs per mile. so if you want to mount your pick up on the propshaft you need to divide 1851 mm by your diff ratio. ie 1851 divided by 3.62(sierra) equals 511.325mm. i think

[Edited on 4/11/06 by martthefridgeman]

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Your speedo will probably have pretty detailed instructions with it. Although the circumference can be calculated using the tyre data you'll get a more accurate measurement by physically measuring it - roll your car onto the drive and use chalk to mark the tyre and ground, push the car until the tyre mark touches the ground again, mark the floor there, and measure the distance between the two marks.

I'd recommend doing your best to get it accurate before taking it to the SVA, if your speedo is the same as mine then you set the circumference by flicking a series of 8 switches on the back of it. Once your speedo is mounted in the dashboard and has a heap of wires surrounding it it's not easy to get out and adjust!

Pete

it is a mk 2 escort diff , is that any good?

I used an acewell
pushed the car outside
mark the floor and tyre
my magnet is on the propshaft
I pushed the car up the road and counted
the prop rotation for 10 times
then marked the floor
measured that distance divided by 10 and
put that figure into the acewell
spot on for the sva
no need to know diff ratio/tyre size

done it . many thanks for your advise.

at a guess, escorts come with 3.54 and 3.89 i think. Maybe wrong, im sure someone can correct me if so. Do your calculations/observations match either of these?