gear ratio
Lead Driver
Joined: Sep 2004
Posts: 7,208
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From: Wichita, KS
I use a GPS to get my actuall MPH. You need a flat straight section of road and run it both ways to make sure you get a correct reading. Then I use this formula.
New Teeth = (Current Teeth x Speedo Reading)/Actual Speed. You have to pull and count you gear teeth. They make gear with 16-21 teeth and I get mine at the local Ford dealer.
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Tuned
Joined: Jul 2007
Posts: 296
Likes: 0
i dont have a gps yet, but i do know im off by 5 miles an hour with 235s on it, followed 2 dofferent people who were running stock size tires, and im going to go with some 29s which are 1/2 to 3/4 in taller.
Posting Guru
Joined: Mar 2004
Posts: 1,307
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From: MARYLAND
How tall of a tire??
I have 35's on mine with 4:10 gears..
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
Look on the Certification Label for the AXLE Code, post what the code is, I can decode it.
To get the correct driven gear (end of speedo cable) you need the tire size, rear axle ratio, transmission type.
Here are the 6 driven gear choices, all are still available from Ford.
16 / 17 / 18 / 19 / 20 / 21.
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Tuned
Joined: Jul 2007
Posts: 296
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ok im a *******, just looked underneath, and someone replaced the rear end. its still marked 4:10 b2 etc etc from the parts guy. the tranny tag reads as,
k1062 1350-11
259342 e67ac
if someone knows what that means, or better yet, what spedo gear i need that would be great!
k1062 1350-11
259342 e67ac
if someone knows what that means, or better yet, what spedo gear i need that would be great!
Lead Driver
Joined: Sep 2004
Posts: 7,208
Likes: 8
From: Wichita, KS
Friend, you don't need to know what rear end or tranny or anything. Just how fast your are really going and what the speedo tells ya. Then pull your speedo gear on the rear out put and count the teeth and use the formula I posted. Then pick a new gear. If ya don't have a GPS see if you can borrow one or get someone to ride with you.
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Tuned
Joined: Jul 2007
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New Teeth = (Current Teeth x Speedo Reading)/Actual Speed.
so its #of old teeth times spedo reading, divided by?, actual speed?... and the answer is the new gear etc?
im not the best when it comes to the "new math formulas"
so its #of old teeth times spedo reading, divided by?, actual speed?... and the answer is the new gear etc?
im not the best when it comes to the "new math formulas"
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Lead Driver
Joined: Sep 2004
Posts: 7,208
Likes: 8
From: Wichita, KS
Yup! Thats it. I would do a highway speed run. So say when your speedo says 65mph you are only going 60.5 MPH. And you have a 18 tooth gear in it. New tooth count = 18 times 65 devided by 60.5 or 19.33 But that is just an example. The speedo gear is easy to get to. Where your rear driveshaft bolts to you t-case you will see the speedo cable. There is a bolt (7/16th?) That holds the gear assy in place. Remove the bolt and pull the assy out. There is a clip on the end that hold the gear in place. Just pull it to the side and the plactic gear comes off. If you have good eyes the tooth count number may be on the gear. But I would count to be sure. I put a thumb nail in my starting place and use a pencil or a pen to count the teeth. If I have to stop just keep your place and you don't loose count.
If you can't find anyone with a GPS you can use mile markers and a stop watch. But that is not as accurate.
If you can't find anyone with a GPS you can use mile markers and a stop watch. But that is not as accurate.
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Tuned
Joined: Jul 2007
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i have 235s on right now, which is bout 28.8 inches, so im gonna go up to a 29 incher with the 4:10 rear end.
Lead Driver
Joined: Sep 2004
Posts: 7,208
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From: Wichita, KS
The problem is that tires are not same. That is to say that not all 32's are the same and not all 205's are the same. And not only do they very from brand to brand but also from model to model. In many cases a BFG Mud Terrain is slightly different it diameter than an All Terrain. And a P radial is different from an LT radial. But if you use a calculator on another site it says that going from 205's and 3.73's to 32's you need 4.4 gears. Now thats using 27.1" for the 205's and 32" for the 32's. If your tires are listed on the tire manufactures site they some times will give the tire diameter. And we could put in some better numbers and get closer what you have and had.
But I have found that you just need to find out how fast you are really going when the speedo says 60 mph and go from there with the formula I posted. And that is just going to get you close. Then you will need to round up or down to the gear that is available. There is not a large number of gears available so you chances of getting it perfect is very slim. But this is the most accurate way I know of.
But I have found that you just need to find out how fast you are really going when the speedo says 60 mph and go from there with the formula I posted. And that is just going to get you close. Then you will need to round up or down to the gear that is available. There is not a large number of gears available so you chances of getting it perfect is very slim. But this is the most accurate way I know of.
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