There is a school zone in a close-by neighborhood that has a "Your Speed is XX" electronic sign that has a built-in speed radar. I set my speed control to 40 mph and with no other cars around, I drove by the sign and it says 38 mph. I wonder if my speedometer is off by 2 mph or could it be the radar sign?

As a test, I drove 60 mph (using speed control) and timed myself through a one-mile length. It took 63 seconds. Therefore, I was goining 57.14 mph, and not 60, as I would have thought.

Is this something the dealer can calibrate? Could it be the 18" rims? Maybe my RX is calibrated for 17" rims?


.

 

i wonder how accurate the sign is

 

That's why I did the "1 mile in 60 seconds" test to narrow down the culprit. It appears that the sign was working fine.


.

 

Most manufacturers build their spedometers to be a bit optimistic (2% seems to be about normal), so they can't be held responsible for speeders. As your tires wear, readings will get just a bit higher.

 

Are the 19" wheel aftermarket? 2% error should be acceptable.

 

I compared my speedometer with a portable GPS system and my speedometer was 2 MPH slow at 60 MPH. In other words, speedometer at 60 MPH and GPS at 58 MPH! I have standard 18" wheels.

2008 RX 350

 

This raises a corollary question: What source does the nav system use for the trip computer's speed indication? Is it GPS, a different sensor, or...? For vehicles without the nav system, it can't be GPS; what do they use?

My RX300 was about 3 MPH slow: with the speedometer painted on 70, the trip computer (that one didn't have a nav system) said 67. My RX350's about 2 MPH slow the same way.

 

This is an interesting topic. We all just take their word that speedometers are calibrated and true.

 

Too many things that influenece what is being dicussed.

Vehicle speedo: Is based on rpm of wheels. Tire wear, tire inflation, turning (not straight line) all affect speedo .. and the gauge (analog) has tolerance.Contrary to the general understanding, the circumfrence/dia of the tire remains the same when you go to a different rim size (aka wheel size) from the manufacturer. Aftermarket stuff can throw the thing off (even tires can).

side note: german vehicles are supposed to be +5-2% in dispaly error, while others can be +/-5%. IN trying to center the variation the german speedo will typically show you higer speed.


GPS: (non-military) The built in error is +-15% intentionally done. Mesures positon and infers speed. It shows only straight line.

Laser/sonar: Can be fairly accurate for straight line (and subject to false reflections). Claibration is an issue.

Law enforcement need to calibrate their equipemnt regularly or the citation can be thrown out.

Unless it is for academic interest (or therads like this), 2% error is acceptable. The resolution on the dial is 5mph (marking increments).

Salim

 

I see the same with mine, speedo reading is 2-3 mph more than acutal. However the odometer appears to register slightly less than actual (based on mile marker observation) which actually is every so slightly in my favor. I know it, I'll live with. I think I'd rather be ticket friendly.

 

I made a mistake in asking an officer re: his calibration sticker.....needless to say, I got the ticket. But he was full of hot air anyway, he was imagining my speed. Those were the days, though, now I do not feel a need to speed.

 

How you get a speeding ticket with a conversion van

 

It was not the van (the van is the wifey's ex-car) when I got the ticket. I was stopped on my CRV. CRV's are not that fast, at least not when I drove it. The CRV is now the daughter's daily.