Speedo / Odo calibration

[roboldham]

Hi folks

 

My recent import's speedo seems to be slightly inaccurate (I know this is usual) - but on my last import vehicle, after the kmh to mph conversion it was spot on (both measured with a GPS)

 

It's reading about 100 when doing 92.5mph at the moment.

 

Anyone know how to calibrate more closely? (okay, okay, call me a stickler)

 

R

[Gaz Walker]

Originally posted by roboldham

Hi folks

 

My recent import's speedo seems to be slightly inaccurate (I know this is usual) - but on my last import vehicle, after the kmh to mph conversion it was spot on (both measured with a GPS)

 

It's reading about 100 when doing 92.5mph at the moment.

 

Anyone know how to calibrate more closely? (okay, okay, call me a stickler)

 

R

 

Hi...

 

No help at all regarding calibration, however speedos are only supposed to overread by upto 10% out, simply due to manufacturers tolerances. They aren't supposed to under read at all though!

 

Gaz.

[THOR Racing]

Hi Rob,

 

I would suggest that maybe the needle of the speedo dial has been moved OR the speedo converter is at fault. (just inaccurate)

 

I make and sell speedo converters with a +/-10% calibration scaling. I can make this +/-5% 0->20% or what ever you like. 16 steps to calibrate the speedo.

 

Most of the time the +/- 10% in 1.25% steps is fine for most people.

 

This is mostly for people who have changed the rolling radius (i.e larger wheels or tyres than stock) or changed the rear differential gear ratio. I've sold some to Australia where they have changed gearboxes. I've sold some to Fensport when they fitted a Celica GT4 engine into a 1.3 Corrolla with GT4 gearbox.

 

See http://www.trlperformance.com/dsc.html

 

The DSC can also be combined with a top speed delimiter, all in one package. Plus it outputs the original speed signal for use by the progressive power steering and auto gearbox (which you need, don't use the modified 5/8ths signal)

 

All outputs are scaled by the same calibration adjustment.

 

The DSC can also be re-programmed (by me) to convert tachometer readings as well. There is a conversion in Hawaii where the Lexus S300 has been fitted with the Supra engine and the RPM dial is out. Also a chap with a Nissan 200SX with a Skyline engine will be using one to convert his speedo and tachometer.

 

Plus.... yes I'll shut up soon.... I've sold one to a chap with an MR2 who wanted to have intelligent adjustable progressive power steering. Now hes got adjustable assistance.

 

Anyway, if you want to know more drop me an email.

 

[email protected]

Pete

[roboldham]

Thanks for a good input Pete.

 

Where are you based - and do you fit stuff?

 

Just I'm in a wheelchair so can't reach most areas of the enginebay.

 

Cheers

 

R

[Frank]

Hi Rob

 

I had the same problem ,speedo was reading 15mph over right

through the range when checked with GPS.All I needed to do was re-locate the needle back by 15mph.This sounds easy but you cant do it while the car is stopped as the needle was up against the stop.Fixing was tricky had to do it while on the move and it has stayed in the correct position since.

 

Hope this is of some help

 

Frank

 

Jap 1997 MkIV 4 6sp

[THOR Racing]

As both I and Frank say this could just be a needle problem.

 

If the speedo error is an OFFSET! then this is the MOST likely cause of the fault.

 

i.e. if doing 30MPH you're actually only doing 22.5mph then this is showing a 7.5mph offset at ANY speed.

 

BUT if there is an error of 7.5mph at 100mph this is 7.5% error and if the speedo is showing 30mph and you're actually doing 27.75mph (this is 7.5% less than 30mph) then this is a fixed PERCENTAGE scaling error.

 

(which again might still be within the acceptable limits of the manufacturers specs 10%)

 

What you must check is .....

If the speedo is accurate for low speeds and then overreads at higher speeds this can only be correctly by mapping the entire MPH speed range to determine the errors at each point. (Can be done!) BUT this is most likely normal and all cars do this.

 

If the speedo is accurate at low speeds but then underreads at high speed then this is a little more serious as you are more likely to be caught speeding.

 

BUT if the percentage offset appears to be the same across the whole speed range (say at speeds 30,40,50,60,70) then the DSC can correct for this. This is correcting for the accumulation of electro-mechanical errors of the dial.

 

In fact the DSC can correct for a fixed offset but it'a an expensive way of repositioning the needle.

 

So first determine if it's a fixed OFFSET (7.5mph across the whole range) or if it's a fixed PERCENTAGE scaling error 7.5% across the whole range.

 

 

to answer the previous query,

yes I can fit them and I'm in Kenilworth, Warwickshire (Jn15 off the M40)

 

But I know Leon has fitted then and he's in Milton Keynes and Chris Wilson is capable and he's in Prees, Shropshire.

 

Regards

Pete