[Z06] Speedometer errors??
Thread Starter
Racer
Joined: Jul 2009
Posts: 406
Likes: 1
From: Kingdom of Bahrain
Speedometer errors??
On both my previosu C5 and now on my 2007 Z, I am recording a 6% error when comparing the speedometer with my datalogger. The car is registering higher. The tyres are stock size. On the C5 I even went as far as checking the diff
Has anyone encountered this?
The logger is a "racelogic" "performance box". The 'g' outputs from the logger agree with the 'g' outputs in the car.
John
Has anyone encountered this?
The logger is a "racelogic" "performance box". The 'g' outputs from the logger agree with the 'g' outputs in the car.
John
Burning Brakes
Joined: Aug 2007
Posts: 762
Likes: 2
From: SLC UT
I have a Kenwood in-dash nav that has its own speedometer function and it's always right on with my heads-up display. When driving by the "check your speed" setups on the highway it has always been within 1 mph (if those things are accurate)
Racer
Joined: May 2006
Posts: 418
Likes: 3
From: Scotland
The Euro Spec cars - kph speedo - usually read at least 6% high to concur with EEC regulations.
Mine was about 8% optimistic.
I recalibrated mine using HP tuners.
The US home market cars - mph speedo - are usually spot on.
Mine was about 8% optimistic.
I recalibrated mine using HP tuners.
The US home market cars - mph speedo - are usually spot on.
Thread Starter
Racer
Joined: Jul 2009
Posts: 406
Likes: 1
From: Kingdom of Bahrain
John
Why do you always have all the answers?
Mine is Euro spec of course
How did you reprogram it? We tried on the C5 by inputting false tire sizes but that didnt work. I assume there is another way
John
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
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Racer
Joined: Jul 2009
Posts: 406
Likes: 1
From: Kingdom of Bahrain
Team Owner
Joined: Sep 1999
Posts: 41,732
Likes: 1,718
From: Springfield MO
My 09 Z06 speedometer reads within 1 mph compared to my Garmin GPS speedometer, and the Z's analog speedometer reads with 1 mph of the digital speedometer(HUD). MY Mercedes reads 2-3 mph higher the the Garmin. I believe the Garmin is very accurate.
Le Mans Master
Joined: Nov 1999
Posts: 7,695
Likes: 51
From: Imperial Beach CA
Racer
Joined: May 2006
Posts: 418
Likes: 3
From: Scotland
In truth, I have far more questions than I have answers
I noticed on one of the mile runs that I was showing an indicated terminal speed of 187 mph which was rubbish, as the car was standard.
The accurate speed was 173 mph on the day.
The Z06 is plenty fast enough as it is, without the need to exaggerate its speed, and I found the inaccuracy very irritating
I complained about it to GM, and the response I got was that the calibration was optimistic because of the need to comply with EEC regs.
These regs require that a car's speedo must never under indicate it's true speed.
I reprogrammed the speedo with HP tuners - just by trial and error - entering slightly different tyre heights, and checking the speedo readout against my Performance box - till I got it accurate to +1mph
Perhaps before with the C5 you were altering the wrong parameters - perhaps not saving them?
You don't need HP tuners to recalibrate the speedo - some hardware programmes will also allow you to do this.
I have a Hypertech which has this function built in, and I'm sure there will be others too.
Race Director
Joined: Mar 2005
Posts: 10,399
Likes: 26
From: Austin Texas
Do you also compensate for tire wear? 9/32 tread depth new to 0 tread depth worn,used makes a tire diameter difference of over 1/2 inch. Thats nearly a 2% error just on tire wear.
Where do you need 1-2 MPH accuracy?
Where do you need 1-2 MPH accuracy?
Thread Starter
Racer
Joined: Jul 2009
Posts: 406
Likes: 1
From: Kingdom of Bahrain
Answer - On the track
There are 2 straights, one which might be flat in 4th and one which might be flat in 3rd
Currently I shift in both when the big green arrow appears in the HUD. So when i download my data i see that I have not maxed in that gear according to a calculation based on tire diameter and 7,100rpm
That means lost time, a wasted up shift and worse still, a wasted down shift
Watching the rpm on the HUD is a waste of time
I have never heard the rev limiter come on, hence the suspicion that it was the car speedo and not the data logger
Seems I am correct
So all i have to do is recalculate the max speeds per gear by multiplying by 1.06
John
There are 2 straights, one which might be flat in 4th and one which might be flat in 3rd
Currently I shift in both when the big green arrow appears in the HUD. So when i download my data i see that I have not maxed in that gear according to a calculation based on tire diameter and 7,100rpm
That means lost time, a wasted up shift and worse still, a wasted down shift
Watching the rpm on the HUD is a waste of time
I have never heard the rev limiter come on, hence the suspicion that it was the car speedo and not the data logger
Seems I am correct
So all i have to do is recalculate the max speeds per gear by multiplying by 1.06
John
Racer
Joined: Jan 2010
Posts: 293
Likes: 2
From: Atlanta Georgia
I, a '06 Z06 owner, own a company that designs and manufacturers dynos. When I built my first one, I found that the speedometer of the test bike (Ninja 14X) was off by exactly 6%. I checked over my data acquisition to make sure that it was not my mistake. It was not. After closer examination, I determined that the difference was intentional. My reasoning: European countries passed a law forbidding the sale of bikes that would run faster than 300 km/hr (186.4 mph). I found that the bike in top gear hit the rev limiter at a speed of 186.3 mph. Coincidence?? I think not. Furthermore, the tachs are off by a similar percentage. On this particular bike, when the on board tach read 11K, it actually turning about 10,300. Again, coincidence?? More than likely a safety factor to lower the maximum revs achieved. Most people will never know anyway. Just my 2 cents.
Josh
Josh
Racer
Joined: May 2006
Posts: 418
Likes: 3
From: Scotland
You will need to read your file first, and access the 'Speedometer' section.
You just enter the new tyre height and click 'commit'.
The module does the other calculations for you.
You then save the new settings to the ECU
Standard set is-
Modified set is-
Last edited by songman3; Feb 4, 2010 at 05:06 AM.
