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Old 02-21-2005, 04:41 PM   #1
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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.
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Old 02-21-2005, 04:45 PM   #2
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are you on the stock potenzas?
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Old 02-21-2005, 04:49 PM   #3
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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.
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Old 02-21-2005, 04:50 PM   #4
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Quote:
Originally Posted by RX8Bliss
A great safety measure, infinitely better than camping police cars that make idiots slam their brakes.

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.
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...
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Old 02-21-2005, 04:51 PM   #5
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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
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Old 02-21-2005, 04:51 PM   #6
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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
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Old 02-21-2005, 04:53 PM   #7
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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.
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Old 02-21-2005, 04:57 PM   #8
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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.
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Old 02-21-2005, 04:58 PM   #9
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Quote:
Originally Posted by RenoIV
I took a portable GPS with a speed reading out tht 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


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.
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Old 02-21-2005, 05:20 PM   #10
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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.
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Old 02-21-2005, 06:36 PM   #11
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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.
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Old 02-26-2005, 02:06 AM   #12
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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.

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Old 02-26-2005, 02:06 AM
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