Electronic Speedo Calibration

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StewbieC
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Electronic Speedo Calibration

Post by StewbieC »

Needless to say the instructions from Caerbont are less than useless.
Other than driving on a road for a mile in an unregistered car not planning on going for a pre booked test.
Could anyone advise the ball park number entered for a T5 box with a standard 3.9 MGB diff and 15" wires Blockleys tyres.
I can tweak it at IVA if it's out.
Cheers
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Stu
Hawk 289, 66 Mustang Fastback with a 289 maximum smiles per mile..
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clive
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Re: Electronic Speedo Calibration

Post by clive »

These are my calculations.

1 mile = 1760 yards = 63,360 inches

Tyre circumference = 83"

Speedo drive = 3/4 rev per 1 rev of wheel

63,360" divided by 83" multiplied by 0.75 = (number of speedo revs per mile) = 572.53 revs/mile.

Calibration number = Cable turns / unit distance x no. of pulses / sender turns

572.53 x 16 = 9160

So calibration number from the chart is 1110101010

This gave me the following speedo results as per the SVA test.

speedo reading / Actual Speed
35 mph / 33 mph
40 mph / 39 mph
50 mph / 47 mph
60 mph / 56 mph
70 mph / 70 mph
Cheers, Clive.

(If I'm not here I'm in my workshop or on the golf course!)
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StewbieC
T289R Committee
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Posts: 1356
Joined: Mon Oct 13, 2008 12:50 pm
Location: out in the sticks, Shropshire

Re: Electronic Speedo Calibration

Post by StewbieC »

Thanks Clive
As a comparison, if you have an electronic speedo (with a small LCD screen at the bottom) you can check the calibration number by holding the trip reset button and turning the ignition from off to on. After a couple of seconds 5 digits should show and you can let go of the reset button (the first digit is probably flashing at this point. If you turn the ignition off before pressing the trip reset button again then the number will not be altered.
________________________________________________
Stu
Hawk 289, 66 Mustang Fastback with a 289 maximum smiles per mile..
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