I recently replaced the factory Continental tires and went with a smaller wheel tire combo. However, now my speedo is reading wrong (I suspect). I found a calculator that will help me find out how far off my speedo is but it requires the OEM tire size. Does anyone know what size tires came on my truck from Ford?

 

That varies slightly by year, and equipment. You can find the factory tire size on the door tag just inside the driver's side door.

 

If go to tirerack.com and put your truck info in and it will tell you.

 

Sometimes that isn't accurate. The door tag always is right.

 

If Cont's were the OE tire it would have been a 275/70R18E

 

Thanks for the info (BTW with my current tires, I run 56.66 MPH @ 60MPH on the gauge)

Now another question... where would I find the front and rear axle ratios, the transmission ratio (I have the automatic trans) and the transfer case ratio? Another calculator on the same site asks this to find true actual MPH

 

I'm not sure on the front but the back axle should have a small plate bolted on to the cover of the rear cover.
Axle Type
31 — 3.73 non-limited slip, F-250/Excursion
C1 — 3.73 limited slip, F-250/Excursion
32 — 4.10 non-limited slip, F-250
C2 — 4.10 limited slip, F-250/Excursion
33 — 4.30 non-limited slip, F-250
C3 — 4.30 limited slip, F-250/Excursion
36 — 4.56 non-limited slip, F-250
C6 — 4.56 limited slip, F-250
41 — 3.73 non-limited slip, F-350 (single rear wheels)
D1 — 3.73 limited slip, F-350 (single rear wheels)
42 — 4.10 non-limited slip, F-350 (single rear wheels)
D2 — 4.10 limited slip, F-350 (single rear wheels)
43 — 4.30 non-limited slip, F-350 (single rear wheels)
D3 — 4.30 limited slip, F-350 (single rear wheels)
46 — 4.56 non-limited slip, F-350 (single rear wheels)
D6 — 4.56 limited slip, F-350 (single rear wheels)

These came from here post 2 and a couple of other things you might be wondering about your truck. https://www.ford-trucks.com/forums/1...tml#post863208

 

Thanks scraprat...a lot of good info here!

 

Even easier, look on the door sticker.

AXLE CODES:

37- 3.73

3L- 3.73 LS

41- 4.10

4N- 4.10 LS

43- 4.30

4L- 4.30 LS

48- 4.88

8L- 4.88 LS

53- 5.38

5L- 5.38 LS