Speedo Calibration

I just spent a few hours on the freeway between 0 - 150Km/hr, don't tell! I used a portable GPS to calibrate my indicated speed against the GPS. The GPS claims a 0.1% accuracy typically my speedo is underreading by 10%, not a huge issue at low speed but annoying when we see 100Km and it's really just 91km. Since we live in a nanny state Victoria Australia I like to get it right. My car has 18 inch Turbo wheels with rears @ 285/30 tyres. Can the speedo's be calibrated? It would seem reasonably logical that they can given it's electronic. Any thoughs has anyone had there's calibrated. Cheers AD

Hi AD I have a GARMIN Street Pilot (SPIII) and had a friend of mine who is TMU (Traffic Management Unit, similar to Highway Patrol in the USA) use a Laser to detect my speed. As I wanted to find out my 964 C2's speedo accuracy at 100km/h I suggested going to the highway - he said "Stuff it let's just gone down to the overpass over here and do it. I'll wait up there - go down about 2 kms get her up to 100km/h and I'll measure you" The overpass is 70km/h, dual lane and very well made. What a feeling getting up to 100km/h (as per the Garmin), hitting cruise control, flying past other motorists AND the cop (who does nothiung of course except measure my speed) Results: GARMIN SPEED INDICATED 100km/h LASER BY COP INDICATED 100.2 km/h Porsce Speedo indoicated 111 km/h I can now trust the Garmin and as it's portable, use it to get an idea of how far my other vehicles' speedos are out.

AD, not sure if it is possible to install this on the 996, but i have the abbott ERA ( http://www.atrol.com/cx_era.htm ) and it has enabled me to dial in my speedo to be dead on as verified by GPS. my 951 has 17's instead of the stock 16's, so it is nice to know that my speedo is correct. it was a very simple install - only 4 wires. slick little unit.

Mark Your copper friend must be a good lad, I didn't do it !! The 10% error in speed must similarly translate to the odometer, that means the trip computer is wrong too so is the indicated fuel consumption etc. Plus service intervals are 10% too soon so running costs are higher as the tyres don't last as long as you think. Now that would be an interesting case in a warranty issue wouldn't it, our US friends could well exploit this one? Cheers AD

I have tested the odometer on my 996 numerous times and it is about as dead on as you can get.

Have you the same tyres? 285/30. AD

Have you the same tyres? 285/30. 265/35 18

In my 1999 996 C2...passenger recording garmin units reading at my speed callouts SpeedO reading Garmin Unit 1 Garmin unit 2 20 16 16 25 21 21 30 27 27 35 31 32 40 36 37 45 41 42 50 47 47 55 51 51 60 57 57 65 61 no read 70 65 no read 75 72 71 80 76 76 85 82 82

In my 1999 996 C2...passenger recording garmin units reading at my speed callouts. Read accross as P= porsche SpeedO in MPH; G1=Garmin 1 and G2=Garmin 2 P G1 G2 20 16 16 25 21 21 30 27 27 35 31 32 40 36 37 45 41 42 50 47 47 55 51 51 60 57 57 65 61 no read 70 65 no read 75 72 71 80 76 76 85 82 82

My village and the neighboring village have been using unmanned radar units that display your speed as you drive by. My speedometer consistently reads about 10% too high (e.g., speedo displays 30, radar shows, 27mph, or speedo displays 33, radar shows 30). I haven't been able to test this at higher speeds, but most likely, when it reads 77mph, I'm really doing only 70, which should help keep me from getting tickets, but is still bothersome. It would be great if I could just take it to the dealer and have it fixed under warranty before my warranty runs out.

The speedo has a built in offset not an error that is proportional to speed. The readings that JimPDX took show the offset which is a constant 3-4 mph at all speeds. As I understand this is on purpose??

The speedometer reads high. I have been Boxstering for almost 6 years and even back then people noticed this. We blame the Germans and claim they have some kind of law and that is why it is designed to read high. In reality, other cars read high as well. If you drive around with a PST2 hooked up the PST2 will display the true speed on the PST2 screen. Eventhough the speedometer reads high it is said that the odometer is accurate. I do not know of any dealer fix for this as there is no such function on a PST2. If you can convince your dealer it is way off then the cluster is replaced.

Is there a way to correct the calibration of the 996 speedo? odometer?

I don't think this is universal as my electronic speedometer is 1 - 2 mph high at 85. The analog dial is dead accurate. I measured it by using the 5 mile long speedometer calibration signs on I-5 in Oregon and later in California (set the cruise control at an indicated 85 and time the amount of time to travel the 5 miles, then do the math). I have also used the mileage markers at the side of the road and obtained the same results. I guess this means that all of us just have to measure our own cars. Tim