Speedo query

[thepickles]

Hi all

I have a MPH speedo fitted in the bongo, not a face but complete unit as far as I am aware

Question

I am running on 18" alloys with 225 / 45 tyres, I have compared my speedo reding with my Sat nav and the speedo shows 10 mph faster than the sat nav

will this make my odometer out as well and by how much ( maths is not my best subject )

And

what if anything can I do to rectify the problem

awaiting your reply's

Cheers
Steve

[dave_aber]

What speed (on GPS) are you at when the speedo is 10MPH faster?

If you are doing 100 on GPS and the speedo is showing 110 then the odometer will overread by 10%.

Suspect that you are not testing this at 100, more like 50 or 60, so the speedo is overreading by 20% (If reading 60 with GPS showing 50). The odo will overread by the same percentage.

Does the face of your speedo havd "GA5R" printed on it? If so, it's from a mazda 626 and will read in miles/MPH. You can have a MPH face fitted which will leave the odo reading in KMs. impossible to say unless you did the conversion yourself really - but you can easily check if the odo is going up in KMs or miles by driving a known set distance.

FWIW, I have 215/55/17 tyres, and a 626 GA5R speedo - and it reads within 1% of a reference GPS on both speed and distance.

Your tyres are 1.3% smaller than mine, so your speedo should overread by about that amount (If it's a GA5R). I have no idea if/how these can be recalibrated though.

[mister munkey]

It does happen. Mine reads about 5mph fast whatever set of wheels I have on at the time, (I'm on my 3rd variant at the mo)

Its a fiddly job but its possible to ease the needle off with the wrong end of a teaspoon & refit a cog or so back - as it were. This SHOULD give a better result.

I've managed to get used to reading what it is rather than what its telling me, or using the satnav speed on a run.

[thepickles]

Dave ,
Thanks for the reply
It is a GA5R, you learn something new every day

It reads

speedo = 40 mph sat nav = 30 mph
Speedo = 50 mph sat nav = 40 mph
Speedo = 60 mph sat nav = 50 mph
Speedo =70 mph sat nav = 60 mph

and so on always 10 mph out

Mr Munkey

you have just answered my second question can I just move the needle

Next question how do I take it out and what else can I play with when I do



cheers
Steve

[Scott]

Remove the front of the panel (the glass and the plastic surround) then gently remove the pin (stop) so the needles drops. Turn on the ignition to energise the speedo coil and it should line up with the calibration mark on dial.

If not carefully prise it off and re-align it, watch out when removing the black cover as there a two small counterweights that can easily be lost.

Me, being not too bright drove up and down a road, moving it a little bit at a time... Then i discovered the marks

I bought a GA5R fitted it fine then realised it has an orange needle and the rest of the clocks are red, so pulled the red needle and fitted it, its at times like this that you wish you had never touched it in the first place

Scott

[mister munkey]

Lower the steering column & unscrew the four Phillips holding the dash in. Carefully pull out the binnacle, removing the block connecters at the back as you pull it out.

There are 4 (?) screws on the back of the speedo that neec to come off then you end up with the precious GA5R in your mitts.

Gently ease Mr Teaspoon under the spindle end of the needle, keeping a close eye on any tiny parts that may fling themselves out as you do so. These need to go back from whence they came, can be a pain.

[missfixit70]

Remove the front of the panel (the glass and the plastic surround) then gently remove the pin (stop) so the needles drops. Turn on the ignition to energise the speedo coil and it should line up with the calibration mark on dial.

If not carefully prise it off and re-align it, watch out when removing the black cover as there a two small counterweights that can easily be lost.

Me, being not too bright drove up and down a road, moving it a little bit at a time... Then i discovered the marks

I bought a GA5R fitted it fine then realised it has an orange needle and the rest of the clocks are red, so pulled the red needle and fitted it, its at times like this that you wish you had never touched it in the first place

Scott

I didn't do that at all

[dave_aber]

orange needle and the rest of the clocks are red,

Phew. Just had to run outside in the rain to check. GAR5 needle is orange, and so are the other ones on mine. Result. I would have been soooooo miffed if they didn't match (and I hadn't noticed!!)

[Scott]

orange needle and the rest of the clocks are red,

Phew. Just had to run outside in the rain to check. GAR5 needle is orange, and so are the other ones on mine. Result. I would have been soooooo miffed if they didn't match (and I hadn't noticed!!)

I think its just the new shape Bongos that have red needles

[dave_aber]

flash gits!!

[patnben]

It may be an idea to do a distance test with your sat nav. Whatever
you do with the needle it won't change the odometer readings. This
will always be matched to the factory fitted wheels and tyres of the
Mazda 626.

[dave_aber]

As it is a fixed 10mph error at all speeds, it sounds like a straight shift in reading which is required, rather than a re-calibration. Offset error rather than gain error. That being the case, the odo should be reading pretty accurately.

Assuming that the actual calibration (i.e. needle deflection for a given incoming pulse rate) on all GA5R's is the same, then as mine reads within about 1% on 215/55/17 (slightly overreads if anything) then your speedo should overread slightly more on your tyres. To be honest, the position you refit the needle which will adjust your offset will have more affect than the small difference in tyre diameters.

Sounds like if you do a straight 10MPH shift you will be pretty much bang on though - and slightly overreading is better than underreading. Keeps you on the right side of PC Plod.

[thepickles]

Thanks for all the reply's

I will select an appropriate teaspoon the weapon of choice

will update when I have done , perhaps at the weekend

cheers
Steve

[madmile]

What they all said .
You definitely dont want to lose the weights in the needle, and should not happen if you lever the needle off with spoons close to the pin. I use 2 spoons (1 rested on each screw head on the speedo face) put a bit of masking tape on the back of each spoon to avoid scratching the screw heads (people only think its been clocked ). Lever upwards - job done.
The stop pin can be a bit difficult to remove from the front, but not really neccessary as you can press the needle onto the pin just enough to grip it...then twist itpast the pin....then push home. Its always worth a drive upto 30mph ish with satnav on before you put everything back fully. Its quite easy to put the unit back in place without the clear cover or surround as these can be put back on with the unit still in place....just very difficult to remove the clear cover without removing the unit (cracked one trying a few years ago ).