How do I fix my speedo error
 

My 86 Carrera has 16" rims with 225/50/16 inch tires at the rear. I assume the car came with larger diameter tires on 15" rims because at 60 mph the speedo reads about 70 mph. Is there a simple gear change to correct the difference? I would like to keep the original speedo. I would guess this is a common problem since many update to 16" wheels. What are my options?

When I sent my speedometer to North Hollywood for repair (the common odo failure) I included a list of readings from the speedometer vs GPS actual in 10 mph increments from 30 to 80 (reading was about 10% optimistic). Asked them to recalibrate it while it was in for repair and it came back dead nuts on. I can't say if they used the data provided but it is comforting to no longer have to do the math when ever I spot a cop.

I sent my speedo to them specifically to fix the speedo error, and I provided no data at all. They said they didn't need any from me. It came back dead-on-balls accurate from 10 to about 90.

I fixed mine when I had the glass out to repair my odometer. The needle can be move on the pin. I just turned it back, went for a drive to fine tune. Im quite certain this isn't the most mechanically sound solution but it is wicked accurate now GPS verified...

And 225/50/16 is the OEM size tire, assuming 16x7 or 16x8 Fuchs in back.

+1 to what Jp-oh did. I had noticed that my speedo always read about 10mph higher than I was actually doing which I found really annoying. When my wee odometer gear decided to disintegrate, I repaired it myself and before refitting the glass & bezel, simply went for a drive with my GPS and 'adjusted' the needle on the shaft (at rest, and very carefully) until they both matched. Now it is spot-on across the range, so no more guess work required :)

what is the rough cost to have the odo gear replaced and the speedo recalibrated?

Last one I sent to NHS was $150.00.
Some shipping cost too.

Cooper

What is the best way to move the needle by hand? I have removed the glass for cleaning on my 914 and it is a big improvement.
( my 914 is running smaller wheels so the speedo is off)

The way I did it is to simply twist it. That is also the method by which you should remove it; back and forth twisting. Apparently pulling straight up is a sure fire way to bust the pin. The pin that holds the needle is indeed very fine. But a moderate steady pressure against the stops will move the needle. So if you are reading under (I.e going 60 when it reads 70) then twist it all the way clockwise untill you hit the stop then apply some pressure and the needle will move on the pin. Release and test. Vice versa if you are reading over.

The approx 10% error rate is fairly linear.

I was bragging at work about hitting 140 in my 81 on the Ohio turnpike. Next time had GPS to verify. 128 mph.

Get it fixed right. Moving the needle will get you close at 80 mph but the rest of the range is not correct.

Plus, moving the needle will not impact the odometer. It will still be adding miles at a 10% excess.

That's precisely why I decided to send mine to NHS for recalibration. They also cleaned and refurbished all the internals as well as the gauge face. It came back looking brand new. I think the $150 is well worth it.

So what did your Opel GT do on that road?! :D

Speedometer reading discrepancy.......
 

Bob,

Last year when I drove the '87 Carrera from Philadelphia to CA and noticed the difference from the speedometer versus GPS readings. From 60 mph to 100 mph there was very consistent difference of about 10%. For example: At 80 mph reading on the dash, the GPS shows 72 mph, 90/81 and 100/90 ( dash/GPS). So we both had observed this 10% variance.

Another incident was when I passed an Oklahoma state trooper at a high speed (less than 90 mph) and was clocked at 78 mph (traffic ticket) after I lifted my foot from the accelerator!!!! That was stupid (passing a state trooper cruiser) and not paying attention.

Tony

Speedometer error question
 

Sorry to resurrect this post, but read as many speedo posts about error as possible.

My 88 new to me Carrera registers about 7-8 MPH over what my waze and GPS tell me I am going.

I contacted Palo Alto Speedo and Helmut told me they do about 3 a month. He said he can correct the error in the speedo, but not the odometer. He also said typically they are off about 6.5MPH high.

And $185.

Some have had issues there and some not. Does Hollywood manage to get the odometer correct as well? Why the errors and the difference?

I put on a pair of 225 55 16 tires and the error dropped to 5-6 high depending on speed. Changed out tires to 245-45-16's and it now is reading about 7MPH high.

Any new insight on this issue in the last couple of years? Which is the best place to send the speedo?

Some of the speedometers have an adjustable potentiometer that can be used to adjust the speed. Some have drilled a hole just big enough to insert a small screwdriver in the can to adjust it. Generally, if you remove the plastic cover on the back of the speedo you can access the circuit board and with a small screwdriver you can make slight adjustments. Once you make the adjustment, reinstall and compare with your GPS. Repeat if necessary.

http://forums.pelicanparts.com/porsche-911-technical-forum/608707-calibrate-my-speedometer.html

Last time out I used, Foreign Speedometer in SD on University Avenue. Based on a Pelican endorsement. I was traveling and I don't rely on my gas gauge.

$110 and I waited for it...had lunch and was on my way home. They do mail order. I don't know where you live....turn around at NHS and Palo Alto can be a bit of a wait. They ALL do mail order.

Seattle Speedometer FTW

I just gave NHS my tire size and they nailed the calibration.

Good people and well worth it.

Had mine done at NHS around November there and back 2 weeks $150.