Thread: speedo out by 8-10km/h

Originally Posted by blackbuttdisco

Using Australian Design rules means the speedo must not show more than 100k when you are doing 100k. It is ok for the vehicle to be going slower than what the speedo shows.

I thought the opposite of the bold bit was true and that is what your second sentence means.

My Defender is on standard tyres and the speedo has always given a high reading. When I fitted a GPS some years ago I found that at 100kph on the speedo it was doing about 92/93.
As mentioned already, it's the car manufacturers protecting themselves. They don't want bad publicity (and payouts) when someone is sticking to the speed limit by the speedo but gets a ticket.

A mate who used to work at Ford confirmed that they deliberately have the speedo read high.


Colin

I've noticed in several vehicles the relationship between GPS speed and indicated speed does not seem to be linear; i.e. it varies across the speed range by varying percentages. Typically about 6-8km/hr over-reading at 100k. 10% seems excessive. Would be interesting to calculate the difference in rolling radius between new and worn-out tyres, loaded and empty vehicle etc, wouldn't be more than a few percent I think.
You would need a smaller driven gear on the cable to increase the cable RPM.
I wasn't aware of the electronic adjusting gadget. Another item for the want list.

Speedo repairers can build a ratio box. This is an inline geaxbox that corrects these speedo issues. It is placed in the speedo cable usually up under the dash.
I had one made up years ago.

I love the comments up higher...

"My speedo is out by 10%... At 100km/h I'm actually doing 90...."

Umm.....

Every defender I've ever known has been out by about 10%. Fitting 255/85 sized tires will make it accurate.

Originally Posted by flagg

Every defender I've ever known has been out by about 10%. Fitting 255/85 sized tires will make it accurate.

Same with mine. Closer to 8-9% on a Def though.

flagg;

why would 255x85 change it to the correct speed, would'nt 235's do the same??
as mine is out as well, i have a transfer out of a td5, behind the 200tdi, lt77 combo and it's out by 10 kph, would like to make this correct. i am running 265,75 16 at's, but i do have a set of road tyres at 235-85-16, would they bring it back to whats normal for a landy anyway??

cheers wally