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Old 05-13-2004, 11:30 AM   #1
SCutchins
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2004 Forester XT
Cayenne Red Pearl

Default Speedometer accuracy

I checked the XT's speedometer on the way to work this morning with a handheld Garmin eTrax Legend GPS with WAAS enabled, unfortunately I didn't note the accuracy but it was a sunny day so it should have been very good. I set cruise on 60 and on flat ground the GPS was reading consistently between 58.9 and 59.1.

In case anyone is interested.
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Old 05-13-2004, 02:24 PM   #2
wolf4wd
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I get similar results. When I have the cruise set to 60 mph on my GPS (Garmin Street Pilot III, external antenna, usually 9 - 17 feet accuracy) my speedo reads 62ish. When it comes to the mile markers on the road, my GPS is dead on where the odometer seems to be off by a bit.
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Old 05-13-2004, 03:15 PM   #3
Ghostrider600
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Not that they're highly accurate, but the local police have put up one of those radar-sign "you're going too fast" things on my regular route, and with cruise set at 60mph I routinely get a reading from the sign that's 2mph off.
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Old 05-13-2004, 03:47 PM   #4
Hondaslayer
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The speedometre reads on average 3mph high.

Safety margin I guess.
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Old 05-13-2004, 07:44 PM   #5
swingkid
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Maybe it'd be accurate if you had brand new tires? Assume a bald tire is 60cm diameter, if the original tread were 1cm thick that would corelate to a 62cm diameter. With a bald tire you'd be going 60 but reading 62 on the speedo.
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Old 05-13-2004, 10:19 PM   #6
MK19_
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My speedo is 2 mph slow (even tho it's a WRX, most Subaru speedo's are the same internally)- had it radar checked
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Old 05-14-2004, 09:56 AM   #7
SCutchins
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Quote:
Originally posted by swingkid
Maybe it'd be accurate if you had brand new tires? Assume a bald tire is 60cm diameter, if the original tread were 1cm thick that would corelate to a 62cm diameter. With a bald tire you'd be going 60 but reading 62 on the speedo.
The XT only has 700 miles on it so the tires can't get much newer. It will be interesting to check it again when the tires have some wear on them, see how much more off the speedo is.
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Old 05-14-2004, 01:23 PM   #8
brett s
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Mine reads about 3-4% higher than I'm actually going. Not a suprise, most are the same these days - there was an interesting article in Car & Driver about that, pointing out some of the regulations that exist in the various countries on speedometer accuracy that allow readings that are high but not slower in many cases. The vast majority of vehicles they've tested in recent years read high...

My plan is to change to a 225/60/16 tire when the OEM ones are toast - fill out the wheelwell a bit more, and make the speedomter a bit more accurate at the same time.
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Old 05-14-2004, 07:24 PM   #9
Back Road Runner
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I went by one of those Police speed boxes they set out. Going 55mph, it read 53mph. I check mile marker signs before as well. I was highing the next mile on the odometer a hair earlier each time. It sucks that my miliage(and warranty) is affected by this.
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Old 05-14-2004, 07:49 PM   #10
Ghostrider600
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Quote:
Originally posted by Back Road Runner
It sucks that my miliage(and warranty) is affected by this.
This is really my big problem, I don't mind the inaccuracy in itself, I mind the corrolary effect of shortening my 60,000mile and 36,000mile warranty coverage.
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