I have a f150 4.6 2wd with 315/75/r16. I have 3.55. What gears should I get and what would my rpm's be?? When my speedo says 70, i am actually doing 80.

 

All,

Since there is a thread already open on this issue. I would like to ask this question since BPardo19 has the same tires as my vehicle.

What effect does having bigger tires effect gearing? I am getting a 6 in lift done to my vehicle and will put 315/75-16 on it. What is the recommend gearing for this set up or can I run on what I have. Not going to do any pulling. My average driving speed is about 55 miles per hour. I don't have a have foot in other words.

Thanks.

 

BPardo19: What kind of driving will this truck see MOST OF THE TIME? I have run 4.10s with 35"s before, and that was a good setup for a lot of highway traveling. I see you have the small V8. I dont know what kind of power it makes, but I assume not a ton. To get a great low end grunt, as well as slightly higher highway rpms, you can go with 4.56s. I think 4lo.com might have some rpm/gearing tables that you can figure that stuff out on.

MartinJose: The debate on gears and tires comes down to one factor...mechanical advantage. When you run a larger tire with stock gears, the mechanical advantage is lessened. You feel this by having to get into the gas more often, for sustained times. Not only do you have a larger diameter working against you, but you also have a larger rolling mass (that extra tread can weigh quite a bit), and greater wind resistence from the lifted rig. The easiest way to understand mech. advantage is to think of a see-saw. When the mechanical advantage is lessened (short gears and big tires), you need to extert more energy to accomplish the same goal (in the see-saw instance, the side that you are applying force to would be smaller, so you would need to extert more on it). With taller gears (read: longer board on your side of the see-saw), the force is lessened to do the same work. I would have the same recommendations about gearing for you as I did Bpardo19. You might also want to check out that 4lo.com site.

 

WheelMA1,

Thanks for the response. So what I understand is that it will be better to change the gear ratio to 4.56. What will happen if I run on the current factory gear ratio. Based on your information, I will not get good gas mileage.

Also, what does a gear change consist of, how much does a gear change cost and where can I find the parts. As you can see, I am not to familar with this.

Thanks.

Martinjose.

 

I have 285/75R16s on my F-150 4x4 5.4L with 3.55s. It moves along quite fine, but my 285s were only about .5'' taller than the stock 265/70R17s that were on the truck before.

I would think that 4.10s would work out pretty good on 35" tire, and 3.73's would get you better mpg (possibly), but towing would be a pain.

 

I drive about 50/50 highway/city. I want more power, but I want my engine to last.... I dont want to be going 55mph @ 3000 rpm. Right now with 3.55 with my 35's, @ 60mph I am at about 2050 Rpm(on my speedo), which is probably wrong because my speedo is off due to my tire size.

 

If I drive on the highway and city equally, what gear should I get. I want to be able to peel out, I cant with 3.55. I also want reasonable gas miliage. What gears should I get? 4.10 or 4.56