Hello everyone! I am a new member here, and this is my first post. I drive a '78 F-250 reg cab 4x4, 460 with T-19 4 speed, Dana 60's front and rear with 4.10s and 4" suspension lift. When cruising down the road at 60, shes turnin out 3200ish RPMs. I am wanting to change that with tires and ZF 5 speed (thats for another day). My first question is about the tire size. I want to purchase the MT CLassic II wheels with BFG Km2 37X12.50X17 tires. I think they should fit okay but I thought I would ask before I go spend $2600... TIA

 

35s would be good with 4.10s and overdrive.

 

I will put 35s on if need be but the taller the better, that why I am asking if she will tuck the 37s alright.

 

Depends on the wheel offset and overall width of the tire. Plus tire height/width varies from manufacturer to manufacturer...


I'd be more concerned whether the tires making contact with the frame, body, or leafs at full lock...

 

I share the same worries. Thats what I meant to "tuck" the tires alright, asking if they would rub or not. If they rub a little here or there when I am off road, no big deal, but if they rub constantly then I wont go that route. Just trying to knock down the RPMs as much as possible witout taking the 4.10s out.

 

Ah... OK. My reference on "tuck" was how far they stuck out.


The 4.10s need not be removed if going with an overdrive. In fact, they'd be about perfect with 35s or 37s for a mild rig... See, ya gotta think of the each piece of the RPM vs speed equation.. tire height, trans gear ratio, and final drive ratio. I know you're planning on an OD trans later but that's something you have to think of now.

 

I have done the math and figured with the combo of the 37" tires and the ZF 0.77 5th gear, the revs would be closer to 2200 at 60 MPH which would be miles better than what is is now. I know the BFG KM2s are 36.8" in diameter and 12.5" wide on a 10" wide wheel. I just don't know if they need to be offset, or if the tires will rub in the first place.

 

That is too much tire for a 4" lift with suspension compression and turning wheels at the same time.

I ran that exact wheel/tire setup with 6" lift and it was about perfect Imo.

I will post pics tomorrow.

 

 

Okay, I will go with 35's then. Thanks somethingclever, I appreciate your feedback. Nice looking trucks you have! I would love to own a crew cab someday....