Speedo Adjustment

[nexussteve]

My speedo is out by approx. 5-10MPH (Still needs to be confirmed)

Is it actually possible to adjust the speedo?

(I did a search on speedos, got through 10 pages of problems with rev counters and dodgy needles before giving up and posting this! )

 

[jc1234]

did you find it by the accruate speed of a gps, car manufacters actuualy put the speedo at a lower speed than the car is going for saftery reason, as the car gets older, so there know you not speeding but at least going that bit slower

 

[nexussteve]

Well I had just changed dials from standards to Super S.

Should've mentioned that in the previous post!

Obviously, the Super S dials themselves have a different spacing between each MPH tag, but I didn`t think it would make so much difference!

 

[joesouthgate]

Trust me all K10s and cars of that age will be like that! My K10 was 7-10mph out untill i put 15s on it and then it was accurate! I just used satnav for the speedo.

 

[nexussteve]

So there's no way to adjust it?

 

[joesouthgate]

I dont think so no! just get used to it, old cars wear out. Just get a satnav like i did

 

[SammoHung]

there is some adjustment possible of the tension of the return spring in the speedo....When Iplayed with one on the bench, there diddnt seem to be a great deal of rotation on the adjust screew but it must be there for a reason...

I didnt get around to checking how much speedo needle adjustment is gained by the maximum screw rotation.

The errors are not a fixed ammount of mph....but it is a certain percentage error...(on mine at an indicated 33 I am doing 30...and at an indicated 77 I am doing 70)...-> so 10 % error on my wheel & tyre combo.


the needle in the speeddo also is moved up the dail by magnetism ( a spinning magnet on the end of the speedo cable) so slackaning the return spring tension via the screw (or other means?) SHOULD allow the needle to rise higher for a given magnet rotation speed....

but again I dont know how much needle adjustment this will give?

 

[Ed]

You need to change the spring rate, that is the only way this can be done if you know what your doing. I am going to do my one on the ST when I get it back on the road.

The spinning magnet creates 'Eddy' currents in the non spinning piece which acts against the force of the magnet, moving the needle.

There are two things you need to get right for it to work correctly, the start spring pre-tension i.e. the load on the spring at 0mph and the return spring rate. If you have to much spring rate it will tend to under read, too little and it will tend to over read, the start spring pre-tension will be where it begins to read and is an adjustable fixed constant.

I.e. the speedo could read 5mph+5% over, you change the pre-tension to cancel out the 5mph bit and then the spring rate to cancel out the % bit.

I should also add, you should do this with brand new tyres of whatever it is your going to use, and also temperature will also affect how it reads since this will change the springs dynamics.

Ed

 

[ollyc98]

When I did my white dial conversion the zero was in a different place so I just pulled the needle off and re-adjusted it lol. It now reads close enough to the speed. After you've been driving a while you get used to what different speeds feel like.
If it feels unnaturally slow you are probably going 30

 

[nexussteve]

Olly

yeah, I had to do this with the rev counter. It was reading 500 Revs with just the ignition switch on! hehe.



Sammo/Ed:

Cheers guys! Will look into this and report back! Might be good for a DIY thread or something, as dial-changing is a pretty popular thing in the forums!