vircotto
join:2002-06-04
Illinois
| How do you determine if your speedometer is accurate?
This may sound silly, but how do you determine if your speedometer is accurate?
I've been doing a lot of highway driving lately and have noticed cars riding my bumper (even when I'm in the right lane and over the speed limit a bit). At first I just thought it was aggressive drivers, but then I considered that maybe I was going slower than my speedometer indicated. On several occasions when traffic was virtually non-existent, I set my speed control at 60 mph and timed myself over 10 miles (determined by the mile markers on the side of the road). I did the math and kept coming up in the 54-55 mph range. (With OEM tires/wheels, btw). Could my speedometer really be off that much? Is there an easy (and inexpensive) way to know for sure? |
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No_Strings
Premium,Mod
join:2001-11-22
The OC | GPS. |
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guhuna
R.I.P Mike
Premium
join:2001-03-31
Brentwood, CA | Or have someone follow you in a different vehicle. Then again that car/truck could be off also. |
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Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
clubs:
| reply to vircotto
Take the vehicle to a speedometer shop and get it tested. If you are running the correct tire for your vehicle and the transmission is original, the speedometer can be up to 3 to 4 miles off in either direction.
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What’s the point of owning a supercar if you can’t scare yourself stupid from time to time? |
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vircotto
join:2002-06-04
Illinois
| There is such a thing as a speedometer shop? (*slaps forehead*  )
Okay, I just Googled for one in the Chicago, IL area and came up blank. Is there a better term (or more general term) that I might use in a search?
Or if anyone knows of one in the (far) NW side of Chicago or suburbs, please chime in.
Thanks all! |
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PrntRhd
join:2004-11-03
Fairfield, CA
 ·Comcast
·Comcast Formerly ..
1 edit | said by vircotto  :There is such a thing as a speedometer shop? (*slaps forehead* ) Okay, I just Googled for one in the Chicago, IL area and came up blank. Is there a better term (or more general term) that I might use in a search? Or if anyone knows of one in the (far) NW side of Chicago or suburbs, please chime in. Thanks all! Google "speedometer repair Chicago:
»maps.google.com/maps/place?oe=ut···24517285 |
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Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
clubs:
| reply to vircotto
said by vircotto :There is such a thing as a speedometer shop? (*slaps forehead* ) Okay, I just Googled for one in the Chicago, IL area and came up blank. Is there a better term (or more general term) that I might use in a search? Don't know where they are in relation to you but:
Speedometer & Clock Co
2337 S. Michigan Ave
Chicago, IL 60616-2104
(312) 842-6377
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What’s the point of owning a supercar if you can’t scare yourself stupid from time to time? |
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Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
clubs:
| reply to PrntRhd
Yes, that shows as;
AJR Radio & Speedometer Inc
15549 S 71st Ct,
Orland Park, IL
(708) 429-4114
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What’s the point of owning a supercar if you can’t scare yourself stupid from time to time? |
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greenacres
join:2003-03-13
Manchester, MD
| reply to vircotto
The old fashion way we used to do it. Get and keep your speed up at 60mph and get a passenger to use a stopwatch to clock you between two mile markers. If your speedometer is working correctly 1 mile should take exactly 1 minute  |
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greenacres
join:2003-03-13
Manchester, MD | reply to vircotto
Sorry, you already had that solution listed. Guess that's what I get for posting before having my third cup of coffee!! |
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Waterbug
join:2008-03-30
| reply to vircotto
Your speedometer and odometer run off of the same gears. If you zero your trip odometer at a mile marker and drive in the same lane, it should roll over a mile at every mile marker. At ten miles, you'll get a pretty good idea if it is off. At 60 miles, it will tell you what your speedometer is reading at 60 mph. If it says you've gone 55 miles, then your speedometer is reading 55 mph at 60 mph. If it reads 63 miles, then your speedometer is reading 63 mph when you are driving 60 mph. You can drive at any speed during the test, it shouldn't make any difference. |
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Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
clubs: | Huh? are you saying to go out and drive for an hour as a test for accuracy? |
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Waterbug
join:2008-03-30
1 edit | said by Doctor Olds :Huh? are you saying to go out and drive for an hour as a test for accuracy? First line of the second paragraph of the OP: "I've been doing a lot of highway driving lately" If you're already on the road, it checks accuracy and helps kill the time. Beats counting telephone poles to pass time. |
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CylonRed
Premium,MVM
join:2000-07-06
Bloom County
| reply to vircotto
Our town uses a lot of radar guns with the 'you are going x speed' - I have found them to be pretty accurate between methods. IT can be off that much but it should only be a few % off either way. All of my cars show between 2-5% fast.
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Brian
"It drops into your stomach like a Abrams's tank.... driven by Rosanne Barr..." A. Bourdain |
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vircotto
join:2002-06-04
Illinois
| reply to vircotto
Thanks, folks!
I guess if I can drive to the east coast and back, I can make it down to Orland Park (or S. Michigan Ave.) sometime.
BTW, I did see the listing for the Speedometer & Clock Co last night, but somehow among the bicycle/motorcycle speedometer listings and Speedo listings that were returned, my mind said, "Nah! Can't be what I'm looking for."
P.S. I've intentionally taken multiple runs at those automated radar set-ups that show you your speed. A lot of them seemed to confirm that I'm going almost 10% slower than my speedometer is telling me, but many also show a much smaller discrepancy.
Thanks once again, folks! |
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PrntRhd
join:2004-11-03
Fairfield, CA
·Comcast
·Comcast Formerly ..
| I find many of my area's "instant display" radar units are never calibrated and can be off in either direction.
Most modern digital speedometers are adjusted for the correct display via jumpers on a circuit board, not by changing gears at the transmission.
I cannot research further for your car because you did not post the yr/make/model. |
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joako
Premium
join:2000-09-07
/dev/null
 ·AT&T U-Verse
| reply to vircotto
All the German cars I have owned always indicate on the speedometer a faster speed than the car is actually traveling at. This is by design.
However, the computer has the correct speed so if either you connect a laptop to view realtime data or e.g set cruise control @ 60mph on the speedometer and rest the average speed, it will show something like 57 mph.
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PRescott7-2097 |
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neonhomer
Honoray Mythbuster
Premium
join:2004-01-27
Edgewater, FL
clubs:
·Earthlink Cable Mo..
| reply to PrntRhd
said by PrntRhd :Most modern digital speedometers are adjusted for the correct display via jumpers on a circuit board, not by changing gears at the transmission. Most modern cars are calibrated from inside the computer by using a calibration factor or a pinion factor.
This is not to say that the speedometer needle itself is not accurate. I had my instrument cluster replaced by GM under warranty (bad stepper motors). The one I got back was a reman, and the needle was physically off by 3mph. After complaining for two weeks, GM finally gave me a new one, and it was off by 2 mph. Finally, I just sent it off to be recalibrated and have a transmission temp gauge added.
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"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton |
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ttiiggy
Premium
join:2001-03-27
| reply to vircotto
Toyota Previa: Had to remove the front face trying to fix 'tip meter won't reset'...
The indicator needle has to come off to get the face off. Putting back together, discovered there is no 'flat spot' or other way to tell where the needle is supposed to go on the shaft.
Finally got the GPS out and had wife scrunch me close to the door and she sat close and steer and watch the GPS and when the GPS said "35 mph", I pinged the needle on the shaft. |
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THUD300
Part Of A Complete Breakfast
Premium
join:2002-06-07
Decatur, IL | reply to vircotto
Easiest way is to use a GPS navigation unit, almost all of them display speed over the ground quite accurately.
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Illinois: where the governors make the license plates! |
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