Speedo Odometer accuracy

[Foggy69]

Originally Posted by Pottsy

Because you are removing (say) 6% of the speed pulses, your odometer will accumulate miles at a rate reduced by 6%, and your mpg readout on the computer will also be reduced by 6% (and will probably end up being accurate!!)

A very interesting write-up of a fascinating gadget.
But the quoted part of your write-up concerned me slightly. I thought that the odometer was accurate on the Civic, it was just the speedo was a bit wonky.
But this gadget will remove 5000 miles off the odometer of a car that has done 70000. Is it legal, or ethical knowing have you odometer that under reads

[Pottsy]

I don't actually know how accurate the odo is. Most cars over-read (have a look at the specs at the bottom of this page), and there appears to be no legally required standard. So it doesn't really worry me - and I don't think the difference will make a real variation in value of the car at sale time.

Also, have a look at this....

[Munro]

Originally Posted by Pottsy

I don't actually know how accurate the odo is. Most cars over-read (have a look at the specs at the bottom of this page), and there appears to be no legally required standard. So it doesn't really worry me - and I don't think the difference will make a real variation in value of the car at sale time.

Also, have a look at this....

It looks like up to 4% over optimistic speedos:

- Make us drive up to 4% Slower, (and therefore less likely to lead to warranty claims as less load on the car)
- Reduce the actual mileage our warrantys last for by up to 4%

Car Manufacturers would therefore appear to be clocking our cars in their favour !! I am sure they never realised this and were only doing it to help make people stick to speed limits !?*

[Pottsy]

I've moved the above posts from the thread showing you how to calibrate your speedo, where I commented that you will be adding miles to your odo at a reduced rate if you slow down the speedo pulses to the correct rate.

It seems that the odo is accurate to within 5%, but Honda skew it in their favour (so the car shows more miles that reality, thus reducing terminating the mileage limited warranty prematurely and causing excess mileage charges on leased cars).

This caused some Americans to issue a class action against Honda. Honda now make the 5% error +/- 2.5% on 2007 cars - but I have no idea whether this has filtered over to European cars.

We really don't have anything to worry about with the warranty here, being 3 year / 90,000 miles.

www.odosettlementinfo.com

Honda Odometer Class Action

Maybe we need to do a run and check the odo reading against Google Earth?

[Pottsy]

Please keep all speedo related stuff here:

speedo accuracy (merged)

[Pottsy]

Just done a little 90 mile test:

Using a combination of Google Earth and a decent GPS, my odo as standard over-reads by exactly 2.0%. With the speedo calibrated, it now under-reads by 4.5%

When my car reaches 41,000 miles the odo will in fact reflect true miles done.

At 85,000 miles done, the odo will read 83,000 - not the end of the world really.

[terry]

It doesn't explain how the MPG on the car seems to be reading higher than actual.......the car is measuring how much fuel has been used to travel a distance since restting.
I don't know why cars do not have an optical system (bounce signal off the road surface) like the test places use. it would do away with pretty well all the errors and uncertainties of a mechanical system.
Terry

[Pottsy]

Terry, if the odo reads 2% high, then that will make the mpg 2% high before you get the "amount of fuel" error. As I understand it, the amount of fuel is the amount the ecu tells the injectors to send in. If the injectors have a tolerance, then this will affect the amount of fuel actually used. The programmer will know the tolerance, and will (naturally) err on the optimistic side.

[terry]

Hi Pottsy,
The same value for distance covered is what I use in my spreadsheet, so the error should cancel out between my and the cars calculation, the difference is the amount of fuel used to cover said distance.
I suspect most of the error comes from the metering device being used to measure the amount of fuel used.....measuring liquid flow can be very difficult unless a lot of money is spent on the metering system.

Terry

[Pottsy]

Terry, there is no flow measurement. The ECU tells the injectors how much fuel to inject (by a pulse of varying duration) - it then uses that instruction to work out how much fuel has been used.

[terry]

Hi Pottsy,
Good point...I didn't know that!

Terry