Speedo Correction

[StuBeeDoo]

Is there any way of correcting the speedo when using undersize tyres?
Mine already over-reads by a minimum 10% at anything up to 60mph (checked with Cyclops), so if I decide to go to 205/50's I estimate that it will read 37mph at true 30 as it's already 35mph at 30 on 205/55's.

Examples.....
True 40mph = indicated 45mph
True 50mph = indicated 55mph
True 60mph = indicated 65mph
True 70mph = indicated 73mph
True 75mph = indicated 77mph
True 80mph = indicated 80mph

In the good old days I used to change speedo drive pinion for one that would give the nearest to right reading, but obviously that won't work with the sensor/chopper set-up in the diff.

OK, so I'm being a bit anal here, but I'd like to have it a bit more accurate as I don't have use of the Cyclops all the time.

TIA
Stuart.

[zaust]

This calc should help you out...

http://www.going-to-france.com/Calculator.xls

[StuBeeDoo]

This calc should help you out...

http://www.going-to-france.com/Calculator.xls

Thanks, but the link won't work for me.
I want to be able to actually recalibrate the speedo. There must be a way of doing it, as HGV/PSV tachographs can be recalibrated and they work on electronic impulse too.

[DaveD]

try this one (tire size calc) if the link doesn't work it is in the links section


http://www.e30zone.net/modules.php?name ... link&cid=8

[odbod]

To actually adjust the speedo readings you want one of these

http://jaycar.com.au/productView.asp?ID ... =&SUBCATID
or these

http://www.blackrobotics.com/index.htm

[Brianmoooore]

There's a pot on the speedo PCB.

[StuBeeDoo]

Interesting bits of kit there Odbod. Thanks.

Brian, that's even more interesting, I'll have to investigate that.


Anyone know if all E30 speedo's are as far "off" as mine is?

[Brianmoooore]

Anyone know if all E30 speedo's are as far "off" as mine is?

Yours does seem a little odd. Would be interesting to see the figures above 80 MPH, as it seems to be heading for under reading which is illegal in Germany, and would indicate that yours is faulty.
The couple that I've checked against GPS have both consistently over read by about 7% or so throughout the range.
OBC has been spot on though.

[AndrewL]

There IS a pot on the speedo PCB - sticking out sideways at the edge as far as i remember. I have an article and some photos on one of my computers which shows it. If you send me your email i'll send them but have never figured out how to post pics here. Alternatively you could search as i got them off the internet - maybe even this site; can't remember.

Andrew

[Demlotcrew]

I can get your speedo calibrated to be accurate to 180mph for £35.

Drop me a PM if you like

Its not as simple as adjusting the pot. (which most speedos dont have)

Andrew

[AndrewL]

The link to the calibration thread with photo of the pot is here:

http://www.e30zone.net/modules.php?name ... =calibrate

Posted: Tue Feb 15, 2005 1:39 am Post subject: Speedo/tacho error & calibration

I havent tried it.