Speedometer Correction
(Tyre Match Box)
Last Updated: 17/03/05
Marks 4WD Adaptors is an Australian company, specialising in the design and manufacture of quality accessories that enhance the performance of four wheel drive vehicles.
Speedo Correction boxes (Ratio Boxes) are now available for cable driven and electronic speedometers.
Speedometer correction is required for many reasons, Larger Tyres would be the most common off road vehicle enhancement requiring the use of one of these units.
Differential ratios are also changed to enhance the performance of four wheel drive vehicles, this also changes the calibration of the vehicles speedometer.
Marks 4WD Adaptors now stock ratio boxes to suit two of the most common ratio changes, custom ratios are also available upon request.
If your vehicle was originally fitted with 30" tyres and is now fitted with 33" tyres your speedometer will read 10% slower that the actual road speed and if your vehicle is now fitted with 35" tyres instead of the original 30" tyres then you speedometer will be reading approximately 16.5% slower.
Should your vehicle be fitted with non standard differential ratios and tyres you can contact us to have a custom ratio box made to suit your vehicle.
| This photo shows a ratio box fitted to Land Cruiser with 35" tyres. |
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Electronic Ratio Box
NOTE: This unit is not compatiable with the following vehicle models - Toyota Hilux's fitted with ABS -Toyota Prado automatic models with ABS - Dodge Ram
Electronic ratio boxes are now available for vehicles fitted with electronic speedometers. They are currently available to fit speedometers driven by hall effect type and also Inductive VSS units.
The Hall Effect VSS units can be identified as having 3 wires.
The Inductive VSS units can be identified as having 2 wires.
Some Vehicles fitted with 3-wire Hall Effect VSS's are as follows:
Holden Commodore VN, VP manual and automatic models. VR and VS manual models.
Jeep Cherokee
Rover Land Rover, Range Rover.
Suzuki Jimny.
Toyota Land Cruiser, Hilux, 4Runner, Surf.
Some Vehicles fitted with 2-wire Inductive VSS's are as follows:
Holden Commodore VR, VS automatic models. VT and VY manual and automatic models.
Nissan GQ and GU Patrol manual and automatic models.
The electronic ratio box is unique in that it has two user selectable ratios available, one option for your highway tyres and the other for your off road tyres/fun tyres.
These two options are simply selected using the two position toggle switch mounted on the front of the unit.
Both ratio options are user programmable for example should your normal on road tyres be over or under size the speedometer can be easily recalibrated using the electronic ratio box. Like wise when you fit your off road tyres/fun tyres for the weekend getaway all you would need to do is simply push the switch.
Naturally both of these ratio options need to be pre programmed in your vehicle with the respective tyres fitted at the time of calibration we have found that a GPS is the most suitable device to use.
With this unit your speedometer can be calibrated to an accuracy of less than 2%. Note: Most speedometers are not perfectly accurate though there entire range, this unit will not rectify this problem.
This photo shows a dual program electronic ratio box fitted in a Land Cruiser 80 Series.
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Note: The box has been installed upside down to locate the switch away from the drivers left foot. |
FAQ's
CLICK HERE for Frequently Asked Questions most commonly received by our sales team.
Ratio Box Part Numbers
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Marks 4WD Adaptors 
Last modified:
May 17, 2010
