Speedometer Inaccuracy
 

I took a trip to Vegas last weekend. Had good times, lost a pile of money, etc. On hwy 15, they have implemented these neat little speed detectors on downhills, shows you how fast you are going and tells you to slow down. A great safety measure, infinitely better than camping police cars that make idiots slam their brakes.
So, I'm cruising along and I pass the first such signs, it is flashing that I am travelling at 72mph. Hmm... my speedo is showing 80.... but whatever. Between LV and LA there are at least 3 such signs, so I made sure to check the speedo at each sign. I was slightly perturbed to see that the speedo was off by 5 ~ 7 mph ( I drove back a few times to make sure it was right, and well, it's fun to see how big the numbers go.)
I know that it isn't uncommon for speedo's to be off, but I've never had a car that was off by this much. Hopefully its just my car. I'd take it to the dealer to have em check it out but I can't come up with a good excuse to give to the techie.

are you on the stock potenzas?

My car is spot on, I passed a sign that read 49 and my speedo was dead on with it...I'd get yours checked out, that's well outside the margin of error.

IM0, it annoys the crap out of me, as people slam on there brakes when they see these, because they THINK there is a photo or cop. So either way, still slams breaks, and after you realize it has no photo, people just zoom by anyways. To me its a nuisance, just my thought though.


I'd actually be more suspicious of the machine than your car. I've seen many of these around where I live, and in every car I drive it always seems a bit off....The odds seem more against the silly machine than your car...but this is just my thought...

Those signs can be horrendously off...I passed one in my old car that said I was going about 15 less then my speedo said

I was flashed by an traffic surveillance cam in September.
My speedo showed 108/109 km/h when the flash came.
When the bill came I was clocked at 102 km/h.
I know they use some km/h margin,so I don't think it was that bad.

The bill was 2200 NOK(350$) for 102km/h in 80-limit:(

I recall this being discussed before and the speedometers were reading 2mph faster than the 8 was travelling.
I took a portable GPS with a speed reading out with the 8 and found mine to be consistantly 1.8 mph slower than the speedometer output. Tested at various speeds

5-7mph off is excessive better check it out.

I checked my speedometer using GPS and it was remarkably accurate. Whether that is more accurate than the radar-signs is the question. If you want to read a thread that discusses this as well as odometer accuracy do a search for GPS. I think that second thread that comes up is the one you want.

German magazine Auto Motor und Sport tested the RX-8 about a year ago.
The inaccuracy was 3 km/h at every speed tested.
I.e. the speedo showed 3 km/h more than real speed.
They tested it up to 160km/h.

I'll try out the GPS this weekend.

Incidently, the fastest that I got one of these things to flash me was 124. Good times.

Mine was between 1 and 2 mph off with the stock potenzas and between 2 and 3 mph off with my Pirelli PZero Nero M+S tires. All very normal.

i was part of the last gps thread. my speedo is was off by 1.6 mph using a garmin wass enabled reciever. this is damn close for any car, and much better than the 8% that my vstrom is off.

beers