Gear ratio
Thread Starter
Senior Member
Joined: Jun 2009
Posts: 106
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From: Deer Park, Texas
Gear ratio
Hey guys, I don't post much but i read a lot. I have a 2009 f150 xlt 2wd supercab and what i've noticed is not a lot of people talk about replacing their gears. I have a 3.31 gear ratio in the rear and am thinking about getting a leveling kit and then some bigger rims/tires. Should i also look into getting new gears such as a 3.73 or a 4.10? Or does it not really make all that much of a difference? thanks in advance
Senior Member
Joined: Jan 2009
Posts: 601
Likes: 34
From: Upstate New York
It really depends on a few things. What size tire are you thinking?
Right now you have the highest gear available for that truck (least torque at the wheels). Great for highway fuel economy.
If you have the 4.6 (3 valve) with the 6-speed, your truck should easily handle a 285 (33 inch tire) as it is. You could probably go to a 35" tires and be OK unless you're towing alot. The reason is that 1st gear in the 6-speed is very low to start with.
For you, regearing from a 3.31 to a 3.55 is not worth it. The difference is too small. Going to a 3.73 would be more reasonable. I wouldn't do 4.10's with a 6-speed unless you're going crazy with the tires (37's).
Basically, you're rear end gears are what multiplies your power to the wheels. so a 3.73 increases your torque about 5% over 3.55's, and 4.10's give you about a 10% increase over 3.73's, etc. (these figures are in top gear) in the lower gears, they have a bigger effect.
My advice. do you're lift, add your tires, drive the truck, and see how it handles it. Then make your decision. You may find that's its fine as is.
If you do a little math, you can figure out what the ideal gear is for the tire size. For example, if you have 32's on there now, going to a 33 is about a 4% difference, so for the truck to have the same power and turn the same RPM, you'd need to lower your gear by 4%, (not enough to justify the expense.). Going from a 32 to a 35 is a 10% difference. Add 10% to 3.31 and you get about 3.6. So a 3.55 would be a good choice.
It's a 2wd, so a gear change is relatively inexpensive.
Right now you have the highest gear available for that truck (least torque at the wheels). Great for highway fuel economy.
If you have the 4.6 (3 valve) with the 6-speed, your truck should easily handle a 285 (33 inch tire) as it is. You could probably go to a 35" tires and be OK unless you're towing alot. The reason is that 1st gear in the 6-speed is very low to start with.
For you, regearing from a 3.31 to a 3.55 is not worth it. The difference is too small. Going to a 3.73 would be more reasonable. I wouldn't do 4.10's with a 6-speed unless you're going crazy with the tires (37's).
Basically, you're rear end gears are what multiplies your power to the wheels. so a 3.73 increases your torque about 5% over 3.55's, and 4.10's give you about a 10% increase over 3.73's, etc. (these figures are in top gear) in the lower gears, they have a bigger effect.
My advice. do you're lift, add your tires, drive the truck, and see how it handles it. Then make your decision. You may find that's its fine as is.
If you do a little math, you can figure out what the ideal gear is for the tire size. For example, if you have 32's on there now, going to a 33 is about a 4% difference, so for the truck to have the same power and turn the same RPM, you'd need to lower your gear by 4%, (not enough to justify the expense.). Going from a 32 to a 35 is a 10% difference. Add 10% to 3.31 and you get about 3.6. So a 3.55 would be a good choice.
It's a 2wd, so a gear change is relatively inexpensive.
Last edited by driver444; May 6, 2010 at 08:43 AM.
Senior Member
Joined: Oct 2009
Posts: 1,290
Likes: 18
driver has given you some great information.
In case you want to seriously look into changing rear end gears, here's some more:
2010 6-speed tranny gear ratios
1st: 4.17:1
2nd: 2.34:1
3rd: 1.52:1
4th: 1.14:1
5th: .86:1
6th: .69:1
And here's a link to a page with an effective gear ratio calculator (software installs on your PC).
http://dygytalworld.ehost-services13.../_support.html
It's about 1/2 way down under the utilities pull-down, "Gear Ratio Calc v1.2".
In case you want to seriously look into changing rear end gears, here's some more:
2010 6-speed tranny gear ratios
1st: 4.17:1
2nd: 2.34:1
3rd: 1.52:1
4th: 1.14:1
5th: .86:1
6th: .69:1
And here's a link to a page with an effective gear ratio calculator (software installs on your PC).
http://dygytalworld.ehost-services13.../_support.html
It's about 1/2 way down under the utilities pull-down, "Gear Ratio Calc v1.2".
Thread Starter
Senior Member
Joined: Jun 2009
Posts: 106
Likes: 1
From: Deer Park, Texas
I was looking into getting some 33 inch tires actually. do you know if i'll have to get my speedo recalibrated to take into account the bigger tires? i have the 18 inch stock rims and i'm not exactly sure the tire size. i just know they look small on my truck, lol
Senior Member
Joined: Oct 2009
Posts: 1,290
Likes: 18
Yes you will have to get your PCM re-programmed for the larger tires IF you want your speedometer and odometer to be accurate. However, even if you get the odometer PERFECT, the Ford speedo is going to read 1-2 MPH high.
Or you can use a GPS and determine how much you're off and then live with the mental "how fast am I really going" calculation.
Or you can use a GPS and determine how much you're off and then live with the mental "how fast am I really going" calculation.