Speedo error more than 7%

impulse · **Posted:** Sun Nov 05, 2006 7:37 pm

Perhaps this has been commented on, but I didn't see a thread.
My 200 km trip to the cottage changed to 184 with the Liberty . I have since checked it with GPS and both the speedo and odometre are out by >7%.
Great for warrenty but even has an effect when calculating MPG.
100 kph true speed shows as 108kph
100kph on the speedo is really 93kph
My tires are standard 225/75-16
Is there a accuracy rule?

litton · **Posted:** Sun Nov 05, 2006 7:52 pm

This seems to be typical of the Liberty. I measured mine on a 450 mile trip and found the Odo to be 6% low and the Speedo 3 mph high at all speeds from 10 mph to 86 mph, not a percentage.

Outback · **Posted:** Sun Nov 05, 2006 8:39 pm

Give it a lift and some bigger rubber.. Mine reads 5% lite running 245/70R17. It started spot on before the lift + rubber..Yours would come out perfect.!
DC told me speedo accuracy should be +- 5% also it can be set by OBCII input ??? .. There is some controversy over if this is really possible..

impulse · **Posted:** Sun Nov 05, 2006 9:49 pm

245/70-17 have diameter 30.6 "
225/75-16 have diameter of 29.3"
Switching to the 17" will make the error larger..

Outback · **Posted:** Mon Nov 06, 2006 6:16 am

impulse wrote:

245/70-17 have diameter 30.6 "
225/75-16 have diameter of 29.3"
Switching to the 17" will make the error larger..

Negative.. He said that he reads high ie Speedo says 100KPH real speed by GPS is 93 KPH larger diameter tyre rotating at the same speed will travel further.
I don't mean to be a smart Ar**!

impulse · **Posted:** Mon Nov 06, 2006 7:47 am

G'day Outback,
You are correct. Sorry. Cold here, brain frozen.

Wilmo · **Posted:** Mon Nov 06, 2006 8:01 am

Mine is now spot on, when compared to the GPS. 100kmh indicated is 100kmh on the GPS. Have fitted BFG 245/70/16's which are quite a bit taller when next to the 235/70/16 goodyear stockies, so it was out from the factory with the smaller tyres. I haven't had the ECU modified.

impulse · **Posted:** Mon Nov 06, 2006 7:27 pm

I checked the rules for accuracy. 10% error is allowed.
Outback : Changing the tire size to larger will make the speed more accurate. but will increase the odometer error. The wheel will rotate fewer times to get to the cottage so the odometer will read less than 184 km whereas the distance is 200 km.

KenJennings · **Posted:** Mon Nov 06, 2006 10:31 pm

impulse wrote:

I checked the rules for accuracy. 10% error is allowed.
Outback : Changing the tire size to larger will make the speed more accurate. but will increase the odometer error. The wheel will rotate fewer times to get to the cottage so the odometer will read less than 184 km whereas the distance is 200 km.

Hmmmm.... And this is how one gets an extended warranty on mileage. ;-)

impulse · **Posted:** Mon Nov 06, 2006 11:11 pm

Good for extended warrenty . If your CRD is similar, your mileage is 7% better on your excellent chart.

Speedo error more than 7%

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