C5- Speedo accuracy
Thread Starter
Le Mans Master
Joined: Feb 2007
Posts: 9,296
Likes: 1,531
From: Oviedo Florida
2024 C5 of the Year Finalist - Modified
2024 C2 of the Year Finalist - Modified
2023 C2 of the Year Finalist - Modified
2021 C2 of the Year Finalist - Modified
2016 C5 of Year Finalist
C5- Speedo accuracy
Friends
I posted a thread wondering how fast a C5 coupe was designed to
run at top end ( this day ). I got alot of interesting responces and
I thank you for them. Everyone was commenting about there speeds,
and I wonder how far off GM calculated their speedo's. Average cars
can be off by 5 mph and the higher the speed the more inaccurate
they can become.
Questioin: How accurate do you think your speedo is and do you
think as you get above 100 is it more inaccurate?
Road Pilot
I posted a thread wondering how fast a C5 coupe was designed to
run at top end ( this day ). I got alot of interesting responces and
I thank you for them. Everyone was commenting about there speeds,
and I wonder how far off GM calculated their speedo's. Average cars
can be off by 5 mph and the higher the speed the more inaccurate
they can become.
Questioin: How accurate do you think your speedo is and do you
think as you get above 100 is it more inaccurate?
Road Pilot
Melting Slicks
Joined: May 2000
Posts: 2,974
Likes: 5
From: CenTex Texas
I had a bad speedo a few years ago and can tell you that GM posted a TSB (#83-83-16) stating the following "allowable" variances:
MPH : Variation
20 : +/- 4
45 : +/- 3
65 : +/- 2
As you can see the general trend as speed increases the allowable variance decreases. So i would assume the speedo would be dead-on at 100mph. However over 100mph i bet the speedo will start to lose it's accuracy.
MPH : Variation
20 : +/- 4
45 : +/- 3
65 : +/- 2
As you can see the general trend as speed increases the allowable variance decreases. So i would assume the speedo would be dead-on at 100mph. However over 100mph i bet the speedo will start to lose it's accuracy.
Last edited by 97C5ENVY; Apr 26, 2007 at 08:16 PM.
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,820
From: Charlotte, NC (formerly Endicott, NY)
Accuracy of newer speedometers in cars is not the same as the old pigs we used to drive. In the old cars the speedo was driven by a cable that turned a magnet which induced an electric field for the meter to measure. A lot of things could put them out of calibration. With the new cars the speedometer is still an analog meter but the signal is converted from a digital representation of the speed that the PCM gets from the VSS mounted in the transmission. The speed is calculated from knowing how many times the drive shaft turns per second. A lot more accurate than the spinning magnetic field. Now the analog meter has the same chance of error as the older speedometer analog meter but overall the system is more accurate. However, the HUD just displays the calculated speed and is the most accurate representation you can get depending on your tire size. In most cases it should be dead on.
Bill
Bill
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
