Rear tyre diameter

[burns 01]

Can anyone advise the correct rear tyre diameter or a allowable range that will keep my speedometer error within ADR 18/03 requirements.
I have a 5 speed AAZ-016 and RF 300kmh speedo

Thanks,Burns
RF#104

[Bill Hara]

Burns, is the speedo electronic or mechanical?
An electronic speedo will use a code off of a table that you can download off the Smiths site (CAI or gaugeguys). The code that you program the speedo with depends on your final drive ratio, your wheel circumference and the amount of magnets in the gearbox (6 I think?)

Here is what they say at CAI

Setting the pulses per mile.
The calibration mode is selected by switching on the ignition while simultaneously holding the programming button and waiting for 3 seconds. After 3 seconds release the reset button, in calibration mode the odometer display will flash.
By momentarily pressing and releasing the reset button each number (extreme left side first) can be incremented to your desired value.
When the desired value is selected release the button and wait 3 seconds.
The next number to the right will flash, increment this number in the same way and continue until all the numbers are programmed to your pulses per mile/km.
At the end of the sequence wait 3 seconds and the speedometer will return to normal operation. If you switch off at any time before the end of the sequence no changes will be programmed.

For most of the following calculations you will need to know the number of times that your tyre revolves per mile or kilometre. Stand the vehicle on a flat surface and make a mark on the tyre at the closest point to the ground, mark the floor at the same point. Move the vehicle forwards for one revolution of the tyre and measure the distance covered.
63360 divided by the distance covered in millimetres = tyre revs per km

Measure the rolling radius (RR) of wheel and tyre, from centre of hub to ground in inches/mm

How to calculate the pulses per mile / km (calibration number)
Prop shaft mounted magnetic sensor (magnets or Bolt heads moving past the sensor)
Calibration number = (tyre revs per mile or km) x (differential ratio) x (no of magnets or bolts

Sender driven from transmission cable drive
Calibration number = (cable turns per mile or km) x (number of pulses per sender revolution)
Calculate RR as above.

Push vehicle forwards on flat ground for 6 tyre revolutions and count number of cable turns.
1680 x (cable turns) divided by RR for inches
For mm divide by 25.4

Cheers

Bill

[burns 01]

Bill , I have a mechanical drive.
I`m in the process of tyre selection (17 inch),there apears to be a lot to choose from and a variety of diameters.

Regards,Burns.

[Trevor Booth]

Burns 01
Just fit the tyre of your choice, take the car to an auto instrument dealer and have a ratio change box fitted in the speedo drive line, easy simple no hassle