Checking The Spedo

[59diamond]

There are several checkpoints by my house where as I drive by the system says the speed limit is say 35 MPG and this sign lights up and says your speed is such and such. Are these a very accurate way to check your speedometer. I have driven by over and under the 35 MPG sign and what it indicates my speed is matches pretty close.
I try to say go by with my speedometer reading 40 MPh so that it is exactly pointing at the 40 and check the sign it says 40.
So I guess it is a cheap way to test your speedometer unless you try higher and higher speeds and get pulled over for speeding.

 

[Boink]

I think they are pretty close. As per a thread in the "Pub" I've used the Android phone app called "DigiHUD" (free) and found it to be amazingly accurate (using GPS - might not be so good on steep hills). My speedo reads almost exactly 10% lower. I don't plan on using it with regularity but it was a quick way to learn what the true speeds where on the 10's.

 

[Deleted member 8987]

Not always, and certainly not a legal excuse.
I drive through them all the time.
ALL of my vehicles are off.

The Jag reads 10% high. Averaging the many reader boards in various municipalities, that's what I came up with.
One or two in a town due north of me....35...38.5 (between 38 and 39 on the clock), come around a corner, reads 31. As I approach, 33. As I am just about past it, 34. The next one is so far off it's ludicrous.
Then what is it reading?
I've watched. None of them discern between cars departing or approaching. So, you've got a 25 sign, right where it drops from 35. It reads 38, then 40, then 37 as you approach at 27 on the clock...it's reading the cars accelerating the other way.
But, do enough different ones, keep an idea of the averages, and you should be fine.

My problem is, does the 10% error stay consistent all the way up?
Is 70 really 70 on the clock, or does it change?
Never seen one on a local Interstate to check.

 

[Deleted member 8987]

That said, one cop friend told me when these first started showing up that they took the old, worn out, no longer legally calibrate-able radar units and put them in the reader boards. No way to prove that, but the inconsistencies makes me tend to believe they are at least not regularly calibrated.
I have seen the inside of older ones, and it was a radar gun mounted inside. No idea on the newer ones.

 

[SaxMan]

I've found the signs are reasonably accurate. I have noticed my speedometer that seems to get more inaccurate as the speed increases. It seems well calibrated at speeds up to 50 mph based on the "Your Speed" signs. For instance, when the speedo is showing 70 mph, I'm only hanging with traffic and getting passed fairly regularly. That might not be an objective test, but it sure would seem I'd be passing cars at 70 mph.

I had a friend that used to like to run the "Your Speed" signs to see how fast it would show. Some of them will pick me up on my bicycle. I haven't found one in a location that would put me over the speed limit. I'd like to find a speed camera in a location where I could trip it with my bicycle, but it would have to be on a pretty good downhill.

 

[59diamond]

Testing my spedo on the freeway in San Diego is useless.I was on the freeway on Saturday in fifth gear with my 60 BE in the slow lane and my spedo read 70 MPH and I was being passed by all the cars to the left of me. The speed limit on the freeway is 65 MPH, but nobody follows it. Cars whiz by at 80 and sometimes 90 MPH and the Highway Patrol does nothing about it.
It seems the days of getting pulled over on the freeway for speeding are long gone. What I hate most on the freeway in any of my cars are the jerks that come up right behind me at high speed and then ride my rear expecting me either to speed up or change lanes to let them by. They will even give me the brights or honk to get by. I am doing the speed limit, but it doesn't matter. I refuse to be intimidated by these Jerks and hold my ground. A guy finally passed me the other day after riding my bumper for awhile and then gave me the finger after he finally passed me going probably 80 MPH. I have been almost tempted to slam on my brakes and see to see if the jerk will rear end me, but I know that is not in my best interest.

 

[Jim_Gruber]

Chance are he would be uninsured and then you would not have the lovely '60 Frog anymore.

 

[59diamond]

I was thinking about my subaru.

 

[smaceng]

60 Frog had a calibrated speedo when the gauge was rebuilt....so it should be accurate....
Scott in CA

 

[59diamond]

I remember reading about it in your blog. I still refer to the blog when I am curious about something.
I was more interested in whether the signs that track the speed of your car as you pass by were accurate then wether the speedo was accurate.
There is a weird stop light not far from my house. It has a sensor of some kind and doesn't change to green unless there is a car waiting at the stop light.
I swear it doesn't see me if I pull up to the light to close and won't change to green until a bigger car pulls up behind me. I have had to back up a little to make it see me when no other cars are behind me. It is an entrance to the main drag in Bonita and i guess they want cars to keep rolling on the main drag until it is necessary to change the light to green. It can be frustrating at times as if the light is discriminating against me and my small car.

 

[George_H]

When sombody rides my bumper I never brake.....A quick downshift always solves the problem.

 

[Deleted member 8987]

or a rapid application and release of the e-brake so no lights....

Week or so ago, coming up the hill past the school, posted (well) 25MPH. EVERYBODY does 40. I'm doing 25 in the Jag, come around the corner, cop sitting other side of the road. Flash lights, honk, point behind me to the SUV four feet off my bumper. Geez.....they nailed the brakes, dropped back about 250 feet and stayed that far away.

Of course the copper was busy with his smart phone or some such...