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Speedo


68cougar

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Just wondering what you guys do to recalibrate your speedometers after installing bigger tires. I just put 33's on my daughters bronco so now obviously the speedo is off.
 

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UrbanRedneckKid

UrbanRedneckKid

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You have to change the gear at the end of the cable.

There's good info on it in the tech library.
 
wildbill23c

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I know with the 235's on my 84 the speedo is 3mph off, so I drive slower LOL.
 

68cougar

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Thanks wildbill, I always forget to go look on the ranger side of the site. Now I have to do math, or let my daughter do it she is in college at 16 years old so she should be able to do simple math.
 
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PetesPonies

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It is very simple math. How tall are your original tires that it came with? How tall are your new tires?? Divide the new into the old size and get a percentage. So if the old tire was 28" tall, your new tire is 31" tall . . . 28/31= 90.3%. So you made a 9.7% change. Therefore you need to make the same change in gear teeth of the driven gear in the smaller direction. So if you had a 17 tooth driven gear, you now need a 15.5 tooth gear. Obviously no half teeth :) So you would need a 16T, closest you could get. You would end up with about a 3 % error in my example. So at 60 mph on the speedometer you would really be going 61.8 mph.
 

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i did mine by taking the plastic cover off and pushing the needle down just a bit. and had my cuz do the speed limit til i got right.

i dont plan on getting smaller tires so it was ok for me to do that. but atleast i wont get speed tickets.
 

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That's not accurate. OK, so you bent the needle. That means at "one" point your speed may be accurate. The difference in speed is a percentage. That amount increases as the speed increases, the percentage of course is the same. But the difference in speed changes. I will give you that maybe it's close enough for you. But the difference in speed at 30 mph will be doubled when compared to the difference in speed at 60 mph. Its not a constant MPH difference, its a constant percentage difference.
 
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