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Speedo Accuracy
I have an 80SC. I have 16 inch Fuchs with
205/55/16. Tires. Just got a new GPS handheld (can never have too many toys). The gps calculated trip speed 2-3.5 mph less than the Porsche speedo. All the other cars were pretty much right on. I the speedo reading that off. I cleaned the speedo current and ground about 3 mos ago when I r/r ed the starter |
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02-04-2001, 02:12 PM
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larryboy-
i'd bet most of us up here also have slightly 'optimistic' speedos. mine acts just as yours does. i've heard some estimate theirs as being up to 5mph over at highway speeds... fwiw. ------------------ Adam Nitti ajnitti@mindspring.com www.adamnitti.com '85 911 Carrera Coupe |
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02-04-2001, 02:25 PM
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Porsche speedos are nuctorius for being off, sometimes WAY off. I would be just glad that its only 3 mph off!
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02-04-2001, 02:35 PM
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Larry,
Do you really have 205/55-16 tires on the rear? Are you aware that those are SMALLER THAN THE FACTORY RECOMMENDED SIZE for the rear? If those are the tires you have on the rear and not just the front, then I am surprised that you dont have even more error! ------------------ Warren Hall 1973 911S Targa |
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02-04-2001, 02:38 PM
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Oops. Went out with flashlight (dark here in New Braunfels) to check the rear tires--225/50/16. Is that the right size Warren?
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02-04-2001, 03:55 PM
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Yes, Larry, that is the correct size, and even with the correct tire size, 911 speedometer errors of 5-10 mph on the 'optomistic' side were reported by many magazine testers in the '70s and '80s, so yours is better than average!
------------------ Warren Hall 1973 911S Targa |
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02-04-2001, 04:21 PM
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I have 205-55-16's on the back of my 70-911 and I estimate my speedometer to be nearly 10 per cent optimistic.
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02-05-2001, 06:58 AM
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My speedo is way on the optomistic side. Is that optomism also reflected in the odometer readuing. Sure seems like it to me.
Mrdi |
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02-05-2001, 06:11 PM
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How accurate are the GPS speedos in the first place. IIRC, the military purposely built in a much lower accuracy in civilian systems (+/- 3metres) compared to military ones (+/- 3 cm).
Anyway, my speedo (300 km/h) is between 15 to 20 km/h ( 9-12 mph) optimistic. I've noticed that most of it is because the scale goes from 0 on the first mark to 20 immediately above it. what I did was to pop the glass and carefully pull the needle down to where 0 should be if it was linear and its much better now. |
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02-05-2001, 08:01 PM
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Just for Info:
By German law, speedo's can be optimistic, but must not be pessimistic. Lawyers will say its to prevent speeding, but my impression is it's coming from the car industry. Conclusion: Every Euro-country car's speedo will be a bit optimistic. Jens |
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02-05-2001, 10:58 PM
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In my experience (I hate to admit this here) Toyotas are always off by 5mph.
Quote:
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02-06-2001, 07:35 AM
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Our former President BillyBob ordered the removal of the civilain GPS inaccuracy last year some time. Today civillian units are just as accurate as military ones.
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02-06-2001, 08:49 AM
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Het we don't need no speedo's, just use use the Tach. I calibrated my car over a known distance/time in 3rd,4th and 5th. I have menorized what 500rpm in each gear means. example.... In 5th gear each 500 rpm is almost 12 mph, on the freeway, 3K = about 70MPH,.....close enough for government work!
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02-06-2001, 09:18 PM
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