speedo gear

[Broncoman]

My speedo is about 5 mph too slow at 55 mph(50 mph on speedo). Thats with 31's and 4.11's<br>Does anyone know how many teeth on the speedo gear(has 20 teeth now) i need to have to get it to read right?<br><br>TIA

 

[WyleCoyote]

Nobody should wear speedo's unless they are swimming in the olympics....Oh not that kind of speedo...<br><br>Don't know anything about the gearing! ;D

 

[EricLar80]

You don't need a new gear, you need 33" tires! No, I understand that it is a % thing, so if you are reading 50 at 55, then you are reading about 9% too slow (50/55 = .91). So, to get it back up, you need to run your speedo gear 9% faster, which would be 18 teeth (.91 x 20 = 18.2). Can anyone verify that this is correct? <br>-Eric

 

[Broncobowsher]

I was thinking that it should be 19 tooth out of memory, but there is also something else to consider. The drivING (not driveN) gear, the gear cut into the output shaft, comes in 2 flavors. I think a 7 tooth and an 8 tooth if I remember right. This will make a difference on what gear you need.<br><br>I haven't done enough research to figure out which one is installed for which reasons. I think it has something to do with what diff gears were factory installed.<br><br>Just another fly in the ointment (I watched Die Hard this weekend)

 

[KST1]

I used the information found on this page http://www.broncohio.com/tech/calculations.html<br><br>to adjust my speedo before my vacation trip. Worked great. The new speedo gear cost me $8.50 at my local Ford dealer. I don't know why I didn't do this 7 years ago when I went with bigger tires.<br><br>-D

 

[Broncoman]

So y'all are saying i need a lower tooth count to speed up the speedo? ?:? My cousin's truck was reading way to fast with a 20 , but we changed it to a 17 and it is right on now. That makes me think i need a higher tooth count to speed mine up ?:? <br><br>It had a 19 to start with, but changed it to 20 to see if it would change it.

 

[Broncobowsher]

You just answered your own question<br>Reading fast then add teeth.<br>You need to do the opposite. It is reading slow, so drop teeth.<br>I have also heard that it 1 tooth is good for changing the speedo about 5 MPH (at 60). When I went to 33s, I had to drop from an 18 tooth to a 16 tooth. The speedo was showing 50 MPH when the GPS said 60 before the change.