I am wondering what would be a better choice for gears in my truck. It is a 06 F150 4.2 and a 5speed manual. It currently has 3.55's in it and oversized tires and wheels. Since the tires and wheels it feels like it lost its low end. I am currently only thinking obout 3.73's or 3.90's. It can't break the tires lose unless I am doing 5-10mph, which leads me to suspect a to high of a gear ratio. I do drive alot in the country, city and on the highway, but if I do go on the highway then it is only when I am heading up into the Sierras (siera mountain range). So there are some prety steep hills. I am more of a performance driver and like it to be a quik and respnsive truck. It has bad throttle response when I am driving and floor it.

 

What size tires?

 

275/55/R20, about 32 inches. After playing around with the calculators I am leaning toward the 3.90 but still not 100% sure

 

Is this a 4x4? If so, the costs involved in a gear swap will be quite high. With that said, I would move to 4.10s with that tire size for a good bottom end response. The OD takes care of the highway cruising.

 

There is very little percentage difference between 3.55, 3.73, 3.90. I agree with wheelMA1. 4.10 will increase your highway RPM about 300 if I calculate correctly. ESP with the 4.2 and a 5 speed, I bet it will make the truck lots of fun.

Personally, I want to go with a 4.30 and a 33 inch tire. That should be close to my stock tire and a 4.10. With a good mix of highway and city driving, I'll bet that the MPG's are close to the same if not a smidge better than what you get now.

 

How would going from 3.55 to 4.10 do to my gas millage? I would have higher rpm's, but I would have to give it less gas for acceleration especially in the city. It should hurt the highway a little but improve the city theoretically of course, I would think??

After putting 4.10 into the calculator it really looks good. It will raise the RPM's a little over 500rpm in fourth and a little less than 300 in OD. It makes much less of a difference than I thought, and if I put 3.73 or 3.90 I wouldn't notice a whole lot. I will shift out of first at about 18mph instead of 22mph, which isn't a huge difference but what I was looking for. It should be even better than stock.

OH, almost forgot it is just a little regular cab 2wd so I only have to do the one differencial.

 

Well what did moving to the bigger tires do to your mileage? If it went down, the new gears should help bring it back up to where it was previous. I have always used this as a rule of thumb:

32-33" - 4.10
33-35" - 4.56

 

I am extremely proud tha your 4.2 can spin a tire. I have 295/45/20 on there and if you floor it, it will not even attempt to spin a tire. The only time I can spin a tire is when I have the engine revving pretty hard. My truck has no bottom end what soever. If you plan on upgradign in the futer I would get 4.56. If you are happy with your 33 and have no intentions on upgrading get the 4.10. This would bring you back to where you were stock but I see no need to replace your gears in two months when you will get bored and eventually go with a taller tire. Just my suggestion to plan for the future of your vehicle. Proud that a 4.2 can spin a tire, my silly automatic has to much lag.

 

how much do gears go for? And also, how much do installers usually charge for an installation?

 

To do a complete gear swap on these new 4x4s, Id say 2500+ is a good bet. It is not a cheap upgrade by any means... and cannot readily be done by a shadetree mechanic. Unless you set up the gears perfectly, you can ruin that new expensive set VERY quickly.

 

I wouldnt be scared at all to run 4.56s in these newer trucks. In my lowered 04 i had planned for 4.56 gears with tires about 32 inches or so. I know it sounds high, but many friends of mine have 4.56 gears in their trucks and are reporting great power transfer and their mileage is hardly affected at all.

I went from 3.55 to 3.73, and didnt feel a thing. I wouldnt be at all concerned with going with 4.56 gears

As far as the cost, expect to pay around $200-250 per axle on the ring an pinion, another $100-150 per axle for the install kits (bearings, seals, crush sleeves, etc.) and anywhere from $200-400 per axle for installation. On your truck, you should have the 8.8 31 spine rear, which means that gears and install kits will be a little cheaper and easier to find than those with the 9.75 rear.

 

I am planning for the 4.10's and they are about 185.00-200.00 for a set plus the install kit and the install itself. I'm lucky to only have 2wd for this gear change. I hope it will spin the tires since before the only time I could spin the tires was when the street was wet or if I started on dirt and then on to pavement, if I get them going in dirt then it does fine on the pavement and doesn't slow down the tires.


I have heard from many other people that the V6 with an auto is gutless.