tyre size impacts on ECU

[04HUG]

G'day

I have just done an Approximately 1730 km trip and the odometer says I have only done 1650 km.
This will work in my favour long term for resale value by showing less km.
Some of the problems are fuel usage/distance to empty etc.
It also impacts on the auto transmission especially as I was towing a 3000kg parachute.

Does anybody know of anybody that can recalibrate the V6 ECU to suit larger rolling diameter wheels? I'm now running 265/70/17 from 255/65/17.
I'll be in Brisbane area for a few days.

 

[Rumpig]

I don't think you can correct it in the ecu, you'd probably have to get one of these, although i'm not sure if it fixes the odometer as well. http://www.jaycar.com.au/Automotive...-Accessories/CORRECTOR-SPEEDO-MODULE/p/AA0376

 

[Old.Tony]

The Jaycar unit won't fix the odometer/speedometer/tripmeter figures. The modern D40 uses an aggregate figure from the ABS sensors to calculate distance travelled and speed. The gearbox revolution sensor is used for other things (mostly inside the gearbox but also to verify that the drive train is turning over), but it won't do any corrections to speed/distance for you.

You need to calculate the difference between your current tyre size and the standard tyre size for your car. Then you'll know how much to adjust the apparent km by.

Compare the circumference of the tyre - easy to do. 3.1416*((2 * tyre width mm * profile / 100) + (rim size inches * 25.4) ). Do the same for the other tyre size, then divide bigger by smaller to get a result like 1.0529 = 5% variation. Yours was 3.1416*((2 * 255 * 65/100)+(17*25.4)) = 2398mm and is now 2522mm, or 1.052 = 5.2% bigger.

If your new tyres are larger, the wheels will do LESS revolutions per kilometre so the odometer will read less. If you've got a 5.2% variation and travelled 1650km on the odometer, add that 5.2% - 1650 * 1.052 = 1735.8km actual. If you take into account that there are variations in cornering, actual rolling diameter due to wear and tear and not following precisely the same line along the road that the measurer took - that's pretty darn close.