Improving speedo accuracy

[K@rlos]

After coming back from Ninove I have discovered how truly inaccurate the speedo actually is :shock: 90mph with a 1600dp, really? :lol:

What can I do to make it give a more realistic reading?

Karl

 

[StuF]

Is your rolling radius standard?

i.e standard wheels and tyres?

If so and still over reading it could be down to a worn speedo cable or loose speedo unit - someone probably does recon ones.

Paul (myvanway69) is running standard gear and his speedo is spot on! Exactly the same as my satnav!

 

[Harlequin]

This guy is the VDO fixer, call him about re-calibration....
http://www.jdo10.pwp.blueyonder.co.uk/page2.html" onclick="window.open(this.href);return false;

 

[K@rlos]

I've got 165/70 14 front tyres, no idea that is stock. Although it should make any difference, altering tyres only affects transmission driven speedo :| I think my speedo is just knackered :lol:

 

[sparkywig]

The speedo is connected to the near-side front wheel hub, so any change in rolling radius will affect the speedo reading.

 

[Tofufi]

I've got 165/70 14 front tyres, no idea that is stock. Although it should make any difference, altering tyres only affects transmission driven speedo :| I think my speedo is just knackered :lol:

Speedometer is driven from the front wheel. Smaller rolling radius front tyres like yours will throw the speedometer reading out, as your wheels will be rotating faster at the same *real* speed.

Edit: Damn, too slow :lol:

 

[sparkywig]

Keep up Jim.

 

[sparkywig]

Karlos, use the tyre size calculator about 2/3 of the way down the page to see how far out your speedo is reading.
Stock tyre size is 185C14 which is about an 82% aspect ratio.

http://www.carbibles.com/tyre_bible_pg4.html" onclick="window.open(this.href);return false;

 

[StuF]

Keep up Jim.

:lol: :lol:

 

[aspro]

You can adjust the speedo Karlos. I personally wouldn't bother but here's a step by step. http://www.thesamba.com/vw/forum/viewtopic.php?t=474291&highlight=speedo" onclick="window.open(this.href);return false;

Similar method here too. http://www.itinerant-air-cooled.com/viewtopic.php?f=58&t=8945" onclick="window.open(this.href);return false;

 

[EgoTrippin]

This guy is the VDO fixer, call him about re-calibration....
http://www.jdo10.pwp.blueyonder.co.uk/page2.html" onclick="window.open(this.href);return false;

Just tried this guy but he says he won't re-calibrate VDO speedo's . I will call him on Monday to find out why Terry.

Mine says 90mph when I am only doing 60mph.

Its something I have wanted to get sorted out for ages. Does anyone else know of somebody who can do this work?

 

[Harlequin]

when I am doing 60mph.

That must have been one helluva steep hill Steve :lol: :lol: :lol:

 

[mychatype3]

http://www.tacho-thomas.de/instrumentevwkfer.htm

 

[Geeze]

Ours is out too. So having learnt from the GPS just how much it's out by I just mentally 'translate' what it's telling me (nice 65mph cruise is 73 on the clock, fr'instance)

And don't rely on calculating what it should be from the change in tyre size, they weren't brilliantly accurate to begin with. The speedo in my missus' bug is absolutely bob on when we checked it, so must have been under reading quite badly when it was stock cos the front tyres are a lot smaller now...

 

[EgoTrippin]

when I am doing 60mph.

That must have been one helluva steep hill Steve :lol: :lol: :lol:

I was going up it too Terry

I just spoke with John Ostick. He will repair my speedo as its not working correctly to over read by that amount, but won't re calibrate it unfortunately.

 

[Mags]

I had the speedo on my Austin Healey done by these guy's:
http://www.speedycables.com/calibration.html" onclick="window.open(this.href);return false;
but you would need to check they do VDO first.

 

[EgoTrippin]

I have also been in touch with Tacho Thomas over in Germany (thanks for the link Mycha).

This is his response to the situation, which is more positive

'there are two possibilities to do that.

Number one is to use a small "gearbox" in front of the speedo. The changing is close to 100 %, but it's very expensive. The price is about 200,00 to 250,00 Euro.

Number two is to change gearwheels inside the speedo. The price is 30,00 Euro, BUT (!!!) there is not a gearwheel for every tire-size. So you have to go as close as you can go to the right size.. That means, there could be differences in the miles-counter - The speed-needle is not the problem.'

I'll keep you posted as to how this all pans out.

 

[PIE]

Im using those size tyres and I am roughly 10 mph out at 50, It did start to read up to 90 but that was dust and crap around the mech in the speedo head which I blew out.

 

[EgoTrippin]

I have now got my speedo back from Tacho Thomas. Its taken around 3 weeks from posting to receiving it back, all repaired and recalibrated for a very reasonable price.
I need to go out and do a sat-nav speed trial to see how accurate the speedo is now, but looks pretty close so far.

 

[Mucka]

Keep us updated, was it expensive