Gearing VS Speedo reading?

[sirhk100]

I bought my Explorer with 3:73 gearing and 32" tires. According to GPS my speedo is right on the money so I'm guessing that the previous owner had it calibrated for the larger tires. So, I'm putting in 4:56 gears. If I don't have the speedo recalibrated how far off is it going to be? I've found speed calculators for tire size changes but not gearing changes. Anyone that can give me some info, it would be greatly appreciated!
Khris

 

[Gary Steeber]

Hi Khris, Try going to this link http://www.explorer4x4.com/speedo.html

I believe you are going to off about 12% on you speedo after you re-gear. You should be able to drop down about two teeth on your speedo gear.

 

[Alec]

Don't quote me on this, but:

I believe your speedo will say about 33-34 when you are going 30, and it will say 75-77 when you are going 70.

 

[Robert]

If you are sure that all he changed was the speedometer gear and not the gear ratio, then your speedometer will be 4.56/3.73 times faster (1.22) than you are going. On your '92 the gear is easy to replace, so it would be easy to get another gear provide Ford makes one with the correct numver of teeth for your final ratio. Are you sure that the previous owner didn't already put in 4.10s or 4.56s when they put the taller tires on?

The difference between 3.73 and 4.10 is 22%. At 30 MPH your speedometer will read 37 MPH. At 60 MPH your speedometer will read 73 MPH.

 

[BislamJoe]

He's got 3.73's, well, I may be late with that since he's getting the 4.56's soon, maybe this week?

Khris - Are you gonna get that crazy TTB soon? Let me know how that comes out. I've started to think about the Baja Concepts 4" lift TTB, but I'm really leaning toward a widened unit; though I did finally give in and decide to lift 4" and go to 35's.

 

[sirhk100]

I specifically asked the previous owner about any gear changes and he said nope but he wanted to. I also spun the tire 1 revolution and the drive shaft turned a little of 3 1/2 turns so I'm guessing with that info I can assume that the door code is still what's in it. Thanks for the info guys.

SlamJoe-

I'll post a reply on the long travel thread in the suspension forum.
Khris