I have a 4 x 2 2005 F-150 with 3.56 gears but I hate the get-e-up. Towing is suspicious also. I have been thinking of changing the rear gear ration. Perhaps 3.73 or ...??? Anyone do this???

Help,

Thanks,
Manny

 

If you are going to change, don't bother with 3.73's, go for 4.10's.

 

It's been done a time or two... I was going to upgrade my 4.6 from 3.55s to 4.10s, but instead I decided to more than double my torque instead and go to 3.73s...

 

The best towing mod for 2wd trucks. I agree abotu skipping the 3.73. 4.11 or 4.30, depending on your tire size.

 

I have 32 inch tall tires riding on 20's. I have heard that if I go to 410's I would really get poor gas mileage especially on the freeway.

Anyone know what the engine rpm would be at 80 mph with 3.73's?

How about 4.10's?

 

That's a mis-conception. Some people here with 35" tires have gone from 3.55 to 4.56 and improved fuel economy by 20%, along with better acceleration. Besides being taller than stock tire size, you probably added 25 pounds per wheel which is harder to turn and uses more fuel. 3.73 is only 5% shorter gearing, which only gets you back to stock tire size effective gearing. With the extra weight, you'll want 4.10 gear. I've yet to hear anyone who's actually complained about going too short a gear in an F-150.

I used this calculator for your question.

Overdrive is 0.70:1. Transfer Case is 1:1. Leave RPM blank to calculate.

3.73 @ 80mph = 2193.2 rpm
4.10 @ 80mph = 2410.8 rpm

 

With 32 inch tires I'd probably put 4.30's in it.

 

Thank you guys so much for your help. That calculator is awesome. Now I can make some educated decisions!

 

I have a 01 F150 scab with a 4.6L auto and the 3.55 gear (stock sized tires which will be changed to 285's in near future). So for me to improve my tow capacity, would I go to a 4.10? Doesn't going to a lower geared rear end result in a higher rpms at highway speed and thus higher fuel consumption? I've installed a Hypertech tune to try and improve it, it seems to have worked some. My rv trailer is about 4,000 lbs dry.

 

Yes.

Not necessarily!

NOTHING can increase the capacity above the rating. Regearing can improve the *performance*.

Use the calculator to see what the bigger tires does to your *comparative* ratio. When you change the tires, you need to spend some money anyway to recalibrate the speedometer, see how it performs before spending the bucks for a new set of gears.

 

I went up to 285 tires (33") with the 3.55 gears that came stock with the 4.2L. It was OK but 5th/OD was only good for flat running. Once I started towing regularly - I found it hard to keep a steady speed on the interstate - having to shift between 3rd and 4th a lot.

I went to 4.30 gears. 5th/OD is fine on the highway now and I can tow 5200lbs easily at 65mph in 4th. Gear/RPM spread is much better. Results should be even more noticeable with a V8.

Gas mileage unloaded with 4:30 gears is pretty much the same. 2 mpg better when towing.

Seat of pants guess is that 4.56s would probably work out OK too for heavier towing loads.



Scott

 

My problem is when I am pulling my trailer on the highway, with a slight headwind I am mostly running in 2nd and 3rd to maintain 100 km/hr (60mph). It will mostly stay in 2nd so it is screaming at about 3500-4000 rpms, I cannot hold 100 km/h in 3rd. So, in this case, will a gear change help me out, and if so, what would I look at? 4.10? 4.56?

 

What type of headwind and what type of trailer are you talking about?

 

If you have that kind of problem with stock tires, you will want 4.56 gears for 285.70R17's.

Fuel consumption is based more on throttle position than engine speed. If you raise the engine speed so that there is more torque availible (and shorter gearing), you'll be pushing on the pedal less and using less fuel under certain conditions.

 

I don't know, say maybe a 10 to 20 km/hr (6 to 12 mph) headwind and the trailer is a 1998 Travelaire Drifter, 23 ft. If I try to keep my speed closer to 110 or 120 km/hr (68 to 75 mph) I can hold that speed a bit better in 3rd cause I'm closer to my max power range (I'm running closer to 3500 rpm). However, I don't like driving that fast with a trailer on behind.