Tire/Speedometer chart.... - Defender Source
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  #1  
Old September 26th, 2013, 02:42 PM
skrufy
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Tim Timmins
1987/Defender 110
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Tire/Speedometer chart....

Anybody have a link to a speedometer conversion chart when you change tire sizes? I found one last week on somebody's LR website, thought I book marked it, didn't, and now I can't find it.

It was Defender specific- one part had you plug in the stock tires, then plug in the new tire size, and then the graph would give you the original speedo readings, and then what reading the new tires will indicate. My D110 reads about 8-10mph faster than I'm actually going...

thanks-

Tim
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  #2  
Old September 26th, 2013, 02:45 PM
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Zack
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I always use the tacoma world one, very helpful.

http://www.tacomaworld.com/forum/tir...5r16-255-85r16
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Old September 26th, 2013, 02:49 PM
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Cabell Crowther
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I dont have a chart but I can tell you that with 255/85s (33") the speedos on my trucks are within 1 mph of the gps at any given speed. I think LR designed defenders for 33s but those got axed in the accounting dept.
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  #4  
Old September 26th, 2013, 03:32 PM
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Keith Armstrong
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Okay, I'm a nerd...but that "pi" thing usually works for me...then it's a little ratio comparison...if you really want to, compare your math with a measured mile and a watch...

That's probably what I get for driving across Nebraska alone

http://en.wikipedia.org/wiki/Circumference
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  #5  
Old September 26th, 2013, 03:34 PM
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Quote:
Originally Posted by cabell View Post
I dont have a chart but I can tell you that with 255/85s (33") the speedos on my trucks are within 1 mph of the gps at any given speed. I think LR designed defenders for 33s but those got axed in the accounting dept.
damn, here I thought my odometer is slightly overstated when in reality it might be slightly understated.
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  #6  
Old September 26th, 2013, 03:41 PM
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Russell
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My speedo is spot on the GPS when running 265/75. When running 255/85, 65 on the speedo is 70 on the GPS.
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  #7  
Old September 26th, 2013, 04:06 PM
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Phillip
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My NAS 95 is dead on with 255's, it was about 3mph off with 265's IIRC per the garmin and the trimble
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Old September 26th, 2013, 04:43 PM
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Lee
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Is this the original speedo, or the VDO electronic speedo?

Quote:
Originally Posted by down_shift View Post
My speedo is spot on the GPS when running 265/75.
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Old September 26th, 2013, 05:01 PM
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Russell
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Originally Posted by rover26c View Post
Is this the original speedo, or the VDO electronic speedo?
The original speedo and 3.54 gears w/ the 94'.
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  #10  
Old September 26th, 2013, 07:04 PM
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Jason
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Quote:
Originally Posted by UnfrozenCaveman View Post
Okay, I'm a nerd...but that "pi" thing usually works for me...then it's a little ratio comparison...if you really want to, compare your math with a measured mile and a watch... That's probably what I get for driving across Nebraska alone http://en.wikipedia.org/wiki/Circumference
I did the same thing on a solo trip from Dallas to Jackson Hole, WY... They even have speedometer checks in Kansas, but they're based on 60 MPH... Wasn't willing to slow down, so I had to do it in my head. Anything to pass the time and not have to listen to the Ag. Report.
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  #11  
Old September 26th, 2013, 07:27 PM
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John B.
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A good place to look is the BFgoodrich catalog. It list revs per mile for all their tires.

Using diameters is not accurate as you need to know the actual rolling radius.
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Old September 26th, 2013, 07:51 PM
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Jarrod
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Use the Grimm Jeeper calculator. It will give you any and all information that you are looking for based on gearing and tire size.
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  #13  
Old September 26th, 2013, 09:36 PM
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Mike Simpson
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Quote:
Originally Posted by skrufy View Post
My D110 reads about 8-10mph faster than I'm actually going...
Not likely. Assuming that you have a mechanical speedometer, more likely it's off by a percentage of your indicated speed.

You don't need a chart. Just determine the percentage of your error by comparing your speedometer reading to GPS reading. For example, if your speedometer says 66 mph and your GPS says 60, then you have a 10% error. Remove your existing speedometer gear, and count the number of teeth on the gear. Purchase a replacement gear with a corresponding percentage of additional teeth (in my example, 10% more teeth) since you want the speedometer to read slower.

The speedo gears are color coded, somewhere on the web there is a listing of what colors correspond to what number of teeth.

This is all pretty easy to do unless the speedometer gear adapter is corroded and frozen in the T-case housing, in which case it can be a real bitch to remove.
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