Same here.
speedo vs gps
Thread Starter
Drifting
Joined: Mar 2007
Posts: 1,589
Likes: 1
From: Leelanau County
speedo vs gps
my speedo is approx. 10% faster than my gps. which is right? if it is the vette then i have 6800 more miles on my odo than on the car. (and thats not fair). how to recalibrate?
also keep in mind that this is an export car. 300kph speedo
also keep in mind that this is an export car. 300kph speedo
Last edited by germanc5; Oct 23, 2008 at 06:33 PM.
Thread Starter
Drifting
Joined: Mar 2007
Posts: 1,589
Likes: 1
From: Leelanau County
the car is stock exc. for the exhaust.
also gps agrees with my suburban but disagrees with my v-max. although bikes are notorious for inaccurate speedos.
my wife says she has compared to radar and claims its the speedo at fault.
speedo shop or stealership?
also gps agrees with my suburban but disagrees with my v-max. although bikes are notorious for inaccurate speedos.
my wife says she has compared to radar and claims its the speedo at fault.
speedo shop or stealership?
Last edited by germanc5; Oct 23, 2008 at 06:51 PM.
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Race Director
Joined: Mar 2007
Posts: 18,308
Likes: 21
From: Marlton. Increasing performance one speeding ticket at a time! NJ
OK,
Here's the deal. The only way to 100% acurately gage your speedo is to have a dyno tune. No miscalculation there. Another close way is to put it in cruise control and time yourself between known distances, such as mile markers on a highway. The greater the distance, the better.
GPS is pretty accurate. However, it is only accurate in certain circumstances. The road has to be flat, with little to no elevation changes.
All else equal, I'd wager that the GPS is more accurate.
I had a similar problem with my TransAm. Someone messed with the calibration during gear changes, but did it wrong. Later, after another gear swap, I found out that it was still off. Speed calculators, the infamous 75mph in 3rd gear trick, etc are all inaccurate. Little things like tire pressure and tread wear also contribute to your speedo being a couple percent off.
I used a combination of methods, and the GPS, being paced, measured distances all agree'd that my speedometer was off.
I ended up correcting it with a Diablosport, and then later refining it more with HPTuners.
The ONLY thing that should affect your speedometer in a vette is the tire size. Replace them lately?
Here's the deal. The only way to 100% acurately gage your speedo is to have a dyno tune. No miscalculation there. Another close way is to put it in cruise control and time yourself between known distances, such as mile markers on a highway. The greater the distance, the better.
GPS is pretty accurate. However, it is only accurate in certain circumstances. The road has to be flat, with little to no elevation changes.
All else equal, I'd wager that the GPS is more accurate.
I had a similar problem with my TransAm. Someone messed with the calibration during gear changes, but did it wrong. Later, after another gear swap, I found out that it was still off. Speed calculators, the infamous 75mph in 3rd gear trick, etc are all inaccurate. Little things like tire pressure and tread wear also contribute to your speedo being a couple percent off.
I used a combination of methods, and the GPS, being paced, measured distances all agree'd that my speedometer was off.
I ended up correcting it with a Diablosport, and then later refining it more with HPTuners.
The ONLY thing that should affect your speedometer in a vette is the tire size. Replace them lately?
Intermediate
Joined: Aug 2007
Posts: 25
Likes: 1
From: East Texas
You can check your speedometer accuracy with a stopwatch and a straight uncrowded Interstate Highway with mile markers. Set your cruise on 60 mile per hour. Clock your time between several sets of mile markers. If it averages out to 60 seconds between each set of mile markers then your speedometer is accurate at 60 mph. Speed = distance x time. 60 mph is one mile a minute.
Instructor
Joined: Feb 2006
Posts: 173
Likes: 0
From: Palm Desert Ca
Before Changing C5 Coupe tires to Z06 Sizes (295/35/18) my GPS and speedo were EXACTLY same.
After tire swap the speedo was 2 MPH faster.
Recal'd tire sizes with Predator and they are EXACTLY same again.
After tire swap the speedo was 2 MPH faster.
Recal'd tire sizes with Predator and they are EXACTLY same again.
Pro
Joined: Feb 2004
Posts: 638
Likes: 1
From: Bainbridge Island Wa
I wouldn't bet my license on that. The GPS system is sending a radio signal which is then averaged in a computer chip in your unit. It will always lag in some degree, your actual speed. You might want to do a software download to your GPS or find out if there are any updates for it that aren't installed.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
