speedo nackered

Hairball · Dec 20, 2013

After wondering why my milage per tank seemed so low ie only 190 to the tank,, i checked it against a sat nav to see how far out it actually was,

The speedo reads ok ish with the usual 10% error but the odometer is far from ok. on a journey today the satnav logged me as covering 27 miles and the odometer only read 19 miles which double checking on google maps verryfies the tom tom log..
question is.. as the speedo is reading ok and not jumping about can i assume its the speedo head thats nackered and not anything to do with the drive. i have had a search but havnt found anything describing this problem,, any thoughts...

landowner · Dec 20, 2013

Hairball said:
After wondering why my milage per tank seemed so low ie only 190 to the tank,, i checked it against a sat nav to see how far out it actually was,

The speedo reads ok ish with the usual 10% error but the odometer is far from ok. on a journey today the satnav logged me as covering 27 miles and the odometer only read 19 miles which double checking on google maps verryfies the tom tom log..
question is.. as the speedo is reading ok and not jumping about can i assume its the speedo head thats nackered and not anything to do with the drive. i have had a search but havnt found anything describing this problem,, any thoughts...

Have you got bigger tyres on ?

Hairball · Dec 20, 2013

landowner said:
Have you got bigger tyres on ?

yes it has, and can expect some degree of error due to this but shorley the speedo would be way out as well. by my reconing the odometer is out by some 33%

landowner · Dec 20, 2013

Mine was out by about 10% (fast) until I put 235/80/16 tyres on and now its about 2mph slow at thirty

Hairball · Dec 20, 2013

My speedo still over reads by the usuall 10% accross the board so @ 30 reads 26 , at 40 it reads 36 and so on, so thats about right, but the odometer is way under, i presumed the accuracy of the speedo and odometer would be linked?

Turboman · Dec 20, 2013

Hairball said:
My speedo still over reads by the usuall 10% accross the board so @ 30 reads 26 , at 40 it reads 36 and so on, so thats about right,

Isnt that underreading then?

landowner · Dec 20, 2013

Hairball said:
My speedo still over reads by the usuall 10% accross the board so @ 30 reads 26 , at 40 it reads 36 and so on, so thats about right, but the odometer is way under, i presumed the accuracy of the speedo and odometer would be linked?

They are.

Mine reads 28 when I'm doing 30 and the mpg has dropped accordingly

Hairball · Dec 20, 2013

Turboman said:
Isnt that underreading then?

sorry i got numbers wrong way round, reads 30 actual 26, reads 40 actual 36.. got me holiday head on..

Hairball · Dec 20, 2013

these are the tyre sizes fitted ,,dont know if this helps, these were fitted when i bought
it earlier this year. so have no way of telling what difference the origionals would have made.
goodridge TA 265 70 16 with a diameter of 30.6 in.

Dont know how much these differ from what would have been origionaly fitted

fanatic · Dec 20, 2013

Change speedo drive coloured for different ratio

Hairball · Dec 20, 2013

fanatic said:
Change speedo drive coloured for different ratio

but if i change the gearing wont the speedo then be way out to make the odometer right...?

or does it not work in that way. not trying to be diffecult.. just trying to understand how it works.

Kwakerman · Dec 21, 2013

Sounds to me like your odo is buggered, there is only the cable driving the speedo/odo, if the speedo is working then the cable is fine. What you need to do is find an open clear stretch of dual carriageway, get it up to a steady 60 on the speedo and hold it there, when the odo clicks over to a new mile start a stopwatch, it should take 60 seconds for the next mile to click over. 60 MPH = 1 mile per minute so that will check the relationship between speedo and odo. Once you know that the odo is actually registering the distance correctly you can then look in to getting the actual speed correct if need be.

Pikey · Dec 21, 2013

Just get a prat nav and use that to compare speed & distance covered.

speedo nackered

Hairball

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landowner

Pensioner Pete

Hairball

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landowner

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Hairball

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Turboman

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landowner

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Hairball

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fanatic

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Hairball

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Kwakerman

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Pikey

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