Speedo (Mr. Earl) check

Finally got around to adjust my speedometer to indicate a relatively accurate speed. Indicated speed on my '01 Z3-M coupe was 8 to 10 MPH optimistic.
I basically fed a signal into the rear differential
pick-up wiring and moved the needle on the speedometer to match the OBC reading at 70 MPH.
The following pics are from the car sitting in the garage.





Took the car out today for a medium black raspberry ice cream waffle cone to check the results. The following is based on ascending to the indicated point.

Indicated---GPS----OBC
50----------50-----50
60----------59.9---59.9
65----------64.6---64.8
70----------69.3---69.5
75----------74.4---74.6
80----------79.3---79.5

Descending to the point. Still, pretty good.

70----------68.5---68.7

Much better. Although not a big deal, it's just one less thing to think about, wondering how fast you are going.
More detail on this to come.

Clever hack, looks like it did the trick. Perhaps you could post the details on the DIY board?

Congrats! :thumb:

--SONET

P.S. Hmm, now that I think about it maybe I should devise a way to make my speedo as optimistic as yours was... that along with driving a gear down just might keep me away from a few speeding tickets.

Ron,

any chance we might get some info regarding the OBC install for M coupe owners?

a list of components and maybe wiring guidlines?


*drool*

Ron's info regarding the OBC install was covered in the "other board" as his install progressed. Just hafta do some searching ... although it may be (I haven't looked) his web site now. FYI

Is there a way you could suggest to those of us who do not have the digital read out.
Specifically where are the wires and what is their coding color or ident?
Could you post pics of the wireing hack area.
Thanks, Ron O

Without an OBC, if you know the wiring setup for the OBC (again, research .org or probably better yet, check Ron's site) you could tap into the signal that would go to the OBC and check for the (I assume voltage or frequency) from the pickup. Set the meter up beside you and then find some way to accurately measure your speed as you drive past something at a certain speed (I don't know how accurate those 'this is your speed' trailors are). As you drive the car past the speed indicator, note the reading on the meter. Back at the garage, duplicate the signal into the speedo and do the adjustment.

Ron - how did you 'move' the needle (I have not played with a speedo)?

Originally posted by scottn2retro
Ron - how did you 'move' the needle (I have not played with a speedo)?

Made a tool out of a piece of scrap metal as shown in the following pic. You remove the needle with the tool and push it back on in the correct place.

Ah, now I see why there's a pieces of tape on the speedo face