Speedo Error
Daddylonglegs - 15/8/12 at 09:56 AM
I am running a type 9 gearbox with a 90deg adapter to a mechanical speedo. Not sure what make the speedo is, I bought them off here as a set.
The problem is, when using the Sat Nav to check the accuracy, the speedo is reading very high. I know this is not a major issue reagrds the legality
of it, but it's still a PITA!
An example of the values are:
Speedo--------Sat Nav
---20---------------18
---30---------------24
---40---------------32
---50---------------42
---60---------------50
I know the answer is to buy an electronic one that I can calibrate, but the problem there is the word 'buy' 
Having spent my life savings
getting the car through the IVA and DVLA registration, money IS an object.
So any Locost ideas would be more than welcome guys 
JB
designer - 15/8/12 at 10:37 AM
Wasn't the speedo checked at the IVA?
If so, it should be be within legal allowances.
unijacko67 - 15/8/12 at 11:08 AM
use your speedo readings for 0-60 times, it will be more impressive. lol
Daddylonglegs - 15/8/12 at 11:10 AM
Yes, over limit is fine, it's under-reading that's a fail. The equipment had an intermittent problem but it was still over so OK.
I know the Sat Nav is always different to the tintop speedo (i.e. it shows less than the tintop speedo) so I guess the Locost speedo is not much
further out than the tintop?
Daddylonglegs - 15/8/12 at 11:11 AM
quote:
Originally posted by unijacko67
use your speedo readings for 0-60 times, it will be more impressive. lol
Good point! 
People would know I was lying though 'cos I've got a Pinto!
britishtrident - 15/8/12 at 11:16 AM
If you look at the dial of most mechanical speedos down at the very bottom of the dial in a very tiny font should see a 3 or 4 digit
number which is normally in the range of about 750 to 1700. This number is the TPM , (turns per mile) which should match the number of
turns per mile of the speedo cable.
So either you have find a speedo with a 20% higher turns per mile or alter the gearing of either the speedo drive or the car.
You can also get the speedo recalibrated but this isn't always 100% reliable in the long term.
britishtrident - 15/8/12 at 11:24 AM
quote:
Originally posted by Daddylonglegs
Yes, over limit is fine, it's under-reading that's a fail. The equipment had an intermittent problem but it was still over so OK.
I know the Sat Nav is always different to the tintop speedo (i.e. it shows less than the tintop speedo) so I guess the Locost speedo is not much
further out than the tintop?
Accuarcy of tintop speedos varies greatly most read slightly fast but reading 20% fast is a huge error.
Strangely on tintops with OBD diagnostics the OBD dignaostic speed read out is usually very accurate but the reading on the speedo is usually about
2% to 6% fast.
Macbeast - 15/8/12 at 11:37 AM
Bigger rear wheels ?
If not, Speedy Cables will re-calibrate it for you.
MikeRJ - 15/8/12 at 12:23 PM
quote:
Originally posted by Daddylonglegs
Yes, over limit is fine, it's under-reading that's a fail.
The legal range is +10% to -0%, which yours exceeds by a hefty margin (+25% at 30mph).
Have a word with Speedy Cables, they can re-calibrate instruments.
Daddylonglegs - 15/8/12 at 12:47 PM
Right, looks like a recalibration or new card then.
gremlin1234 - 15/8/12 at 04:53 PM
quote:
The legal range is +10% to -0%, which yours exceeds by a hefty margin (+25% at 30mph).
no, tolerance is 0 to [ +10% +6.25 mph.]
ref: (note 3 of section 17, of IVA M1 Inspection Manual)
you could change the markings within the speedo, or real lo cost, put some marks on the glass
edit: note G.P.S. speedos will inherently 'under read', unless truly straight and level
[Edited on 15/8/12 by gremlin1234]
[Edited on 15/8/12 by gremlin1234]
johnwilders - 15/8/12 at 07:23 PM
When I had mine on the dyno before the IVA my speedo read spot on, my thinking was if the dyno isn’t calibrated spot on I could end up with a fail so
I moved the speedo needle, worked a treat but now its reading 10% fast & I cant be arsed to change it back.