Speedo/ Odometer Calibration Issue - Defender Source
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  #1  
Old August 6th, 2014, 09:16 AM
monktonrover
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Tyler C.
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Speedo/ Odometer Calibration Issue

Hello all- I've currently got 235/85 R16s running on what stock would be 235/70 R16s (along with a 3" OME lift.) As far as my GPS (obviously not 100% accurate) tells me, the speedo and odometer are about ~12% faster than my actual speed (when it's reading 60MPH I'm actually going ~53.) Now- this is contrary to literally every thread and common sense listing I've seen in my research, where it would usually be showing the opposite (that 60MPH reading would be actually ~65MPH.) Am I missing something here? I've double/ triple/ quadruple checked with different GPS devices and programs.

I've checked forums and haven't found anyone with this issue- they usually have the "normal" tire size calibration issue.

THANKS!
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  #2  
Old August 6th, 2014, 10:25 AM
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Jafir Elkurd
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Is this on a D2?
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Old August 6th, 2014, 10:25 AM
ezzzzzzz
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Mark Garrenton
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The gps is dead-on accurate. Did you run the gps with the smaller OD tire? Maybe you were farther off then? Without variations the 235/85 would be 31.73" OD and the 235/70 would be 29" OD. Depending on air pressure, tread and manufacturer variables the OD could change. That aside, did you make any other changes that would change ratios such as a transfercase?

Jafir brings up a good point. If you've got a newer LR with VSS it could be the sender that is jacked up causing the off speedo reading.
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Old August 6th, 2014, 10:36 AM
monktonrover
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Tyler C.
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thanks all. It's a '96 D1 300tdi/ r380. I've only ever tested the speedo and odo with the larger tires, lift and current rig setup. It could be even with stock setup, the gauges are off...The odo comparison I've done against a very accurate mapping software for distance confirms that roughly 12% difference.
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Old August 6th, 2014, 10:39 AM
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John B.
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Quote:
Originally Posted by ezzzzzzz View Post
Jafir brings up a good point. If you've got a newer LR with VSS it could be the sender that is jacked up causing the off speedo reading.
Sig says D2. They do not use a VSS. They use the wheel speed sensors. As you say, the speedo should read low, not high. Unless this is not a D2.....

Write up on installing an adjustable speedo correction box to a D2: http://www.slunnie.com/phpBB/viewtopic.php?t=5
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Old August 6th, 2014, 10:42 AM
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Quote:
Originally Posted by monktonrover View Post
thanks all. It's a '96 D1 300tdi/ r380. I've only ever tested the speedo and odo with the larger tires, lift and current rig setup. It could be even with stock setup, the gauges are off...The odo comparison I've done against a very accurate mapping software for distance confirms that roughly 12% difference.
Okay... You should have said that first....

It just means you have the wrong speedo gear. It can be changed to a different ratio. Any idea on what diff ratio you have?
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Old August 6th, 2014, 10:42 AM
monktonrover
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Tyler C.
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sorry all- D1. My sig was off.

thanks for all the info. I'll just have to figure out how to get everything calibrated.

------ Follow up post added August 6th, 2014 10:49 AM ------

Quote:
Originally Posted by red90 View Post
okay... You should have said that first....

It just means you have the wrong speedo gear. It can be changed to a different ratio. Any idea on what diff ratio you have?

4.11...
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Old August 6th, 2014, 10:52 AM
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This should help: http://www.land-rover-blog.co.uk/how...-a-land-rover/

Since you have no idea what is there, your best bet is to pull the speedo gear and figure out what you have. You want more teeth at a 12% ratio to slow the speedo down. So if you have a 20 tooth, you want a 1.12*20=22.4 ---- 22 tooth gear. to be the closest. Since it is reading fast, you most likely have 4.11s in the diffs.
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  #9  
Old August 6th, 2014, 10:54 AM
monktonrover
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Tyler C.
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yes, 4.11s for sure. thanks so much, that's a wealth of info!
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  #10  
Old August 6th, 2014, 11:21 AM
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Anthony Nelson
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God. Another project. Awesome
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