I have a '06 F-150 FX4 with 3.73 gears. I am planning on installing BFG AT 305/65R18 on my stock rims when my Rugged Trails finish wearin out. I already have 2.5" leveling kit on it. I know the speed will be off about 3 mph but what about the odometer? How much will the shift points be off? Is a programmer necessary for this setup? I know lots of people are running this setup and it looks really good if yall could help me out.

 

Yes, your speedometer and odometer will both be off. How much depends on the height of your oem tires.

 

I have the stock OEM 275/65R18 Rugged Trails on it which measure new at 31.9" and the 305's are 33.7"

 

To give you an idea, my oem tires were 30 inches tall and I replaced them with 33's. My speedo was off 5 mph at 60 mph.

 

wat about your odometer?

 

Never really check it.

 

Is it necessary to put in a programmer with 1.8" difference? Any idea how bad off the shift points are?

 

no, but it may shift a little odd. the only way to really correct this is by regearing. it shouldn't be that serious w/ such a modest increase in tire size. the odometer will be off in your favor, ie reading LESS miles than it actually should display.

 

wen i save up some more money i am def gunna regear

i have 33's on now and i feel like the truck sometimes struggles to "find" the right gear esp. around 40mph or wen going up hill.

 

I have found i need 3.94 to regain performance, for yall who has this setup does it sound right? How much is it to regear? i'd prolly do it myself so does anyone know just the price of gears? And does it correct the speedometer/odometer?

 

I went from the stock 275x65x18 tires to a 315x70x17 tire which is 34.5 inches in diameter. My speedometer was off about 5 mph. The shifting was terrible untill I got an Edge programmer to help out with the shift point's and re-adjust the speedometer for tire size increase. At least it's bearable to drive now but I think my truck still need's some 4.56 gear's to go with the programmer. I think you would be OK with the 305's and a programmer. Just my 2 cent's!

 

Thanks im not really worried about the speedometer/odometer as much as i am the shift points. im really tryin to stay away from the programmer idea tho

 

I don't think you will have any problems if you don't recalibrate the speedo/odo.

 

I have read others threads and some say a dealer can recalibrate the computer to a different size as long it is a optional tire size for the truck and others say it can be any size..so which is it?

 

It is a percentage. Both speedo and odo will be inaccuate by the same percentage. If you increase tire size, then you will actually be running faster than your speedo reads and less milage will be recorded on your odo. With Wandell he was experiencing close to a 10% difference, so the odo would be off by the same.