Question Speedo question

[Bob Elliot Lake]

I’ve discovered that the speedo in my 2000 Base coupe, m6, seems to be reading 8 or 10% higher than my actual speed as compared to a couple of different gps’s. 100 kph on the speedo is actually about 92 or 93 kph. Tire size is stock. Has anyone seen this before? I saw one reference on the corvette forum that seemed to say the speedo does have some electronic calibration adjustment by using an HP tuner, but there were no details. Ideas?

 

[Riley P]

Never heard of this before. I think mine was spot on before I put on the C7 wheels and tires, but if it's reading out that far, it could possibly require a tune?
Is your car an automatic? Which gears do you have in the diff? The auto's came with either 2.73's or 3.15's. if you had 2.73's and put in 3.15's, this could partly explain the difference. Or if you had 3.15 and someone put in the manual transmission gear set of 3.42's, this would almost explain the difference exactly. (Or maybe the cluster was calibrated for a manual transmission car and not for the automatic). If you have a manual in your car, I then have no idea.

 

[Rruuff Day]

I’ve discovered that the speedo in my 2000 Base coupe, m6, seems to be reading 8 or 10% higher than my actual speed as compared to a couple of different gps’s. 100 kph on the speedo is actually about 92 or 93 kph. Tire size is stock. Has anyone seen this before? I saw one reference on the corvette forum that seemed to say the speedo does have some electronic calibration adjustment by using an HP tuner, but there were no details. Ideas?

The satellite's generate several different types of signals. High GPS accuracy for the military guiding Tomahawk missiles through Taliban bedroom windows is a bit different than the signals civilians mostly use and since ground position/time is used to calculate speed, unless you have a dual-frequency receiver, we mostly get a much less accurate single L1 or L2C signal that can also be affected by a lot of geographical and atmospherical conditions. I'd be tempted if you know someone who has access to a speed radar gun to check it that way before I spent much money tuning. I'm sure if you bought an OPP a jelly donut at Tim's some morning and asked him if he would check your speedo with his radar gun, he would probably accomodate you.... JMO

 

[Icecap]

I’ve discovered that the speedo in my 2000 Base coupe, m6, seems to be reading 8 or 10% higher than my actual speed as compared to a couple of different gps’s. 100 kph on the speedo is actually about 92 or 93 kph. Tire size is stock. Has anyone seen this before? I saw one reference on the corvette forum that seemed to say the speedo does have some electronic calibration adjustment by using an HP tuner, but there were no details. Ideas?

This is common even between manufacturers as I found out when I bought my current daily driver, a VW Jetta TDI, new in 2007. I also purchased a new TomTom GPS at about the same time. I found that there was an 8 Km/hr discrepancy between my indicated speed on the speedometer and the speed indicated by the GPS (100 indicated on the speedo was 92 on the TomTom) . All of the research I did regarding this discrepancy seemed to indicate that most car manufactureres calibrate their speedos to read high on purpose although I felt the 8 Km's out at highway speed was a bit excessive.

Since I do most of my own repairs I purchased the Bentley repair manual on DVD for my car and the annual subscription to product information, updates and technical service bulletins. As a result of the TSB subscriptions I was able to trace the speedo issue to a confidential TSB advising all dealers of a factory calibration error of the impulses/mile of the instrument clusters of all Golf, Jetta and Passat on their lot for the 2007 model year. The TSB advised how to recode the distance impulses and using a VAG-COM which is the VW equivalent of a TECH-2 I set the impulse numbers according to the TSB and found that the discrepancy was reduced from 8 Km/hr to 3 Km/hr.

Even before I compared my GPS and speedometer reading I suspected something was wrong since I noticed a big change from driving my Mazda Pickup truck. In the Mazda pickup on the freeway I would most often find that at 10 Km/hr over the posted speed I was going with the traffic flow and not overtaking anyone. In my TDI daily driver at 10 Km/hr over everyone was going significantly faster than I was.

 

[Black 03 Z06]

OPP Officer to Bob, "Would you mind holding my Jelly donut while I finish writing up your ticket".

 

[Bixter44]

We just got back from a Kentucky/Missouri trip and the Garmin Nuvi and the C5 Speedo were the same. Never thought to check them against my phone app speedo just for fun.

I was disappointed that the Corvette Museum didn't have a production C8 on display. Also no '67 big block side pipe car but more than 1 roadster. The C8 on display was a test mule. Not real pretty.

It is really freakin hot down there this time of year. 95 in Bowling Green. The first day we got to Branson it was 97. My C5 handled it better than I did.

 

[YVON ST]

Hello! Better be sure of the problem.The speedo and tach cluster take a lot of time and patience to get at it. If you decide to do it post a thread and i will help you to do it.if you want. Board cost around 60.00 US dollars. Take care Yvon