Tire size and gearing ?
 

On my 04 F-150 4X4 I'm running 265/75/16 tires, I would like to change to over from 3:55 gears to 4:10 gears. Would I be ok with that tire size our would I have to go up to a 285/75/16 or a 315/70/16. Also how does the truck drive with 4:10's and a 5 speed transmission ?

Thanks

You would be fine with your current tires, or you can put bigger ones on - your choice. You should use a programmer to correct the speedo/odo for both the tires and the gears. I understand that the 4.2 5 speed runs VERY well with 4.10's.

You do know you have to do both axles if you have a 4x4 - that's going to be costly.

I'm thinking I may do some of the work myself , how hard could it be, lol. I just did a solid axle swap on a 1995 Bronco.

You will love 4.10s. Review some videos on how to change gears before you give it a try.

Does your truck have the OBDI or II computer? If OBDI, you will have to change the speedometer gears to correct the speedometer I believe. My 95 Mark VIII Lincoln was OBDI but my son's 95 V6 Mustang was OBDII.

04 will be OBD2. Programmer required.

I had 3.55's on mine. I swapped it with 4.10's and have no regrets especially when towing and just regular driving. It makes 1st like a low gear. I usually start out in 2nd when I'm just doing regular driving and it makes skipping gears a breeze.

Normal flat driving for acceleration, I do 2nd, 4th, then 5th. Or sometimes 2nd, then right into 5th depending on my laziness and how far out I rev out of 2nd. 4.10's makes a huge difference.

I remember with the 3.55's, I had to row through all of the gears pretty much.

4.10's with towing makes it way better for hills, especially starting up one. And it makes it easy for someone to learn how to drive standard, being it makes it tad harder to stall the damn thing.

Mind you, I have stock sized tires. And I have the factory Limited Slip. I had it reprogrammed at Ford.

I hate the 3:55 in my truck, they just suck. I'm going to have a local shop install the gears since I don't feel like screwing with them.

Is it better at highway speeds ? With the 3:55 it seems like you always have to give it gas. I'm just happy I don't have a newer truck with 3:30 gears.

Yes it has great passing power. But you sacrifice top end speed.... I think with 4.10's , you'll be lucky to push 90 mph. But I've never tried it nor do I want to, nor do I suggest it.

But you'll have excellent starting power to pull trailers and stumps. All about gear reduction.

Fuel mileage actually went up if I recall, not a lot though. I was expecting it to go down.

Even with 4.10's you will hit the speed limiter (96 mph) in 4th, never mind 5th. You won't be sacrificing any top end, it will just be revving a bit higher.

So with 3.55 your RPM's should be around 1900 @ 70 right? If that is correct then 4.10's would put you @ around 2150 rpm's. Provided your 5th gear is at or near .70.

That's not to bad. I'm not to worried about loosing top end speed. The truck isn't that great over 80MPH anyways lol. That's why I went out and got a GT. I'm looking forward to getting this done. Any suggestions on what gears to buy ? I'm looking at Bronco Graveyard , since they seem to stock them.
Thanks

5th gear in the 5 speed manual is 0.8:1.

Your 265-75-16 tires are approximately 32". At 70 mph in 5th, your rpm's with 3.55's are around 2100. With 4.10's they would be around 2400.

In 4th, you would hit the speed limiter (96) at about 4100 rpm. That would be about 3300 in 5th.

Checked RPMs today on my '04 Heritage, single cab, short bed, 4.2L manual with 4.10s and 285/75R16s. RPMs were slightly above 2500 @ 70 mph. Had 500 lbs load in bed.

With those big tires, you were probably doing more than 70 unless you have corrected the speedo/odo with a programmer.

I have the tire rotations per mile adjusted on the computer along with the gear ratio (stock was 3.55) via a SCT programmer (I have a VMP tune) and I also used a Garmin GPS with WAAS technology. The speedo showed about 2 mph more than the GPS. The lower 2500 rpms was with the GPS speed right at 70 mph.

Edit: Sorry, I just saw a mis-type in my previous post. Tire size is 265/75R16. I have 285s on a different truck.