 Optimistic Speedometer, Thinks I going faster than ctual |
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| barefoot |
 May 7 2019, 03:34 PM
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#1
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Senior Member  Group: Members Posts: 1,370 Joined: 19-March 13 From: Charleston SC Member No.: 15,673 Region Association: South East States 
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I thought the speedo was reading high, today got my first quick readings with a GPS;
these may not be exact but should be close. Speedo GPS reading reading 30 20.7 40 29.6 50 39.7 I have no history on the tranny gearing, but these readings should only be affected by the R & P gears and i didn't think there were any options there. Rear tire diameter is 23.75. Not sure what the OEM size would have been. What's going on here ?? |
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Replies(1 - 3)
| Tom_T |
May 7 2019, 03:59 PM
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#2
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TMI.... Group: Members Posts: 8,321 Joined: 19-March 09 From: Orange, CA Member No.: 10,181 Region Association: Southern California
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Check your tires vs the stock 165/80R15's - it's usually mostly in tire size induced error, & not as much gearing - but then that's a huge speedo error.
https://www.tacomaworld.com/tirecalc (IMG:style_emoticons/default/beerchug.gif) Tom /////// |
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| porschetub |
May 7 2019, 04:12 PM
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#3
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Advanced Member Group: Members Posts: 4,816 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
Wow that are very large difference....even with wrong tyre diameter you would only be out by roughly 2 to 5% ,thinking your speedo might be shot or maybe you cable is on the way out !!!.
Good luck (IMG:style_emoticons/default/beer.gif) . |
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| 914forme |
May 7 2019, 07:04 PM
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#4
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Times a wastin', get wrenchin'! Group: Members Posts: 3,896 Joined: 24-July 04 From: Dayton, Ohio Member No.: 2,388 Region Association: None
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Well the numbers are not linear, they are close but not quite right.
The speedometers work by Turing a magnet inside the gauge with a mother magnet on the shaft that turns in sync, around and around it goes, but if it does something odd it is not directly connected. Odd in this case would be going in reverse. ? is your odd accurate with a measured mile ? It is gear driven, the speedo is driven by a magnetic copasetic function. If the odo is slipping or binding it can cause the speedo to reduce its readings. Not hard to fix, but a pain in the booty to do it right. You have to open it up, remove the drive gear on the Odo shaft it is the first plastic gear you will find, take it off the shaft, measure it. Order one that is bigger from ODOgears, and then sand it to make it fit. Get everything back one, hint tape all the odo gears, and press the gear back on, lube everything up, and reassemble. Again not hard, but not fun. |
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