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Registered
Join Date: Dec 2002
Location: Dahlonega , Georgia
Posts: 14,620
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speedometer/odometer accuracy question
Hello I was driving my 83SC yesterday to Daytona for the 24 hour race and I noticed that by useing the highway milemarkers it seems that my odometer is very accurate,but I have always felt that the speedo reads about 10 mph high,is it possible for the odometer to be accurate but the speedo is not?Also how do you go about figuring out if the speedo is accurate or not?I was thinking of following my wife in her 99 Civic and compare speeds via cellphones,any suggestions are appreciated.My tire sizes are 205/55-16 in front and 245/45-16 in the rear on 7/8 inch Fuchs.Thanks
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02-01-2004, 10:39 AM
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Back in the saddle again
Join Date: Oct 2001
Location: Central TX west of Houston
Posts: 56,070
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you're speedo is probably off by 4-8 mph at 80. Almost all (all cars) speedos are off, usually reading a tad high. The best way to tell for sure would be to use a GPS or a radar/laser gun. You could probably use mile markers. Maybe test against 4 or 5 and use a stopwatch.
245 45 16 are a tad shorter than the stock 225 50 16, but only about 2%.
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Steve '08 Boxster RS60 Spyder #0099/1960 - never named a car before, but this is Charlotte. '88 targa  SOLD 2004 - gone but not forgotten
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02-01-2004, 10:59 AM
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Registered
Join Date: Dec 2002
Location: Dahlonega , Georgia
Posts: 14,620
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So if I was to use mile markers I'm thinking that if you were going 60 mph and if you used a stop watch you would cover 1 mile in 60 seconds,correct?The amount of seconds under/over 60 seconds would be the amount of error?
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2002 Boxster S . Arctic silver + black top/int. Jake Raby 3.6 SS engine " the beast ". GT3 front bumper, GT3 side skirts and GT3 TEK rear diffuser. 1999 996 C4 coupe black/grey with FSI 3.8 engine . Rear diffuser , front spoiler lip with ducktail spoiler . |
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02-01-2004, 11:22 AM
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Registered
Join Date: Mar 1999
Location: Cornwall-on-Hudson, New York, USA
Posts: 4,499
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Don't trust Interstate mile markers. They're often pretty approximately located. Check it against 20 miles or so, not just one. The more mile markers you lose, the lower the percentage of error will be.
Stephan
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Stephan Wilkinson '83 911SC Gold-Plated Porsche '04 replacement Boxster |
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02-01-2004, 11:27 AM
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Registered
Join Date: Mar 1999
Location: Cornwall-on-Hudson, New York, USA
Posts: 4,499
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Meant to say the more mile markers you _use_, not lose...
Stephan
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Stephan Wilkinson '83 911SC Gold-Plated Porsche '04 replacement Boxster |
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02-01-2004, 11:27 AM
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Registered
Join Date: May 2001
Location: Peoples Republic of Long Beach, NY
Posts: 21,140
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VDO Speedometer calibration how to
'86 Carrera Speedometer Calibration?? Speedometer Error. Need some help
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Ronin LB '77 911s 2.7 PMO E 8.5 SSI Monty MSD JPI w x6 |
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02-01-2004, 11:31 AM
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