Speedometers off?
Thread Starter
Race Director
Joined: Aug 1999
Posts: 13,280
Likes: 2,509
From: Bluffton SC via Canton Oh
Speedometers off?
A minor issue. I’ve been driving by one of those electric speed deterrent signs, it’s brand new state of the art. Car constantly registers 2 mph more than the sign. I happen to know a Leo and had him laser my car and yes it’s the same 2 mph faster than he registered.
Just curious anyone else experienced this. Now I know how we get those zero to 60 speeds!
Just curious anyone else experienced this. Now I know how we get those zero to 60 speeds!
Le Mans Master
Joined: May 2016
Posts: 7,106
Likes: 1,546
From: Florida
Just a general comment - Every car I've owned reads slightly higher than the actual speed. This includes a long list of both Foreign, and domestic (GM) cars.
As I understand it, manufacturers do this. Several years ago, and I think it was VW, their speedometers read lower than the actual speed. Of course it resulted in numerous lawsuits from owners who argued they received speeding tickets even though they were sure, by their speedometers, they were not speeding. And, independent engineers hired by the lawyers proved it.
So, the theory is, Mfgrs do this to be on "the other side" of the issue.
As I understand it, manufacturers do this. Several years ago, and I think it was VW, their speedometers read lower than the actual speed. Of course it resulted in numerous lawsuits from owners who argued they received speeding tickets even though they were sure, by their speedometers, they were not speeding. And, independent engineers hired by the lawyers proved it.
So, the theory is, Mfgrs do this to be on "the other side" of the issue.
Safety Car
Joined: Jul 2019
Posts: 4,079
Likes: 2,414
From: Florida
Check it against GPS. Most cars read 1 to 2mph high but I haven't found that to be true with the C8. Mine is pretty much spot on with GPS.
The signs are probably literally never calibrated unlike radar guns that are regularly calibrated
The signs are probably literally never calibrated unlike radar guns that are regularly calibrated
Melting Slicks
Joined: Feb 2023
Posts: 2,368
Likes: 2,495
From: Northern Virginia
2023 C8 of the Year Finalist - Unmodified
Built-in by design.
A speedometer is calibrated to read correctly with new tires of a certain circumference and the manufacturer will always error on the right side (in your favor).
If it read the opposite, in some states, it could end up being the 1-2 mph that took you from speeding to reckless driving (or worse).
It would also end your warranty sooner as the displayed ODO and actual miles would be off. Ask Honda (and some others) about that….
A speedometer is calibrated to read correctly with new tires of a certain circumference and the manufacturer will always error on the right side (in your favor).
If it read the opposite, in some states, it could end up being the 1-2 mph that took you from speeding to reckless driving (or worse).
It would also end your warranty sooner as the displayed ODO and actual miles would be off. Ask Honda (and some others) about that….
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