I was looking into the all the posts about gear and differential upgrades and i read a couple things i'm unclear about. I'm looking to go from a 3.55 to a 4.10 on account i'm getting bigger tires. Does this increase horsepower and if so by how much? Will the gears mess with my transmission? and would i have to use a micro tunner to replot my shift points? Thanks very much for your time and help on this site. Sorry if i asked anything stupid. I'm young and learning.

 

Installing a lower gear ratio (higher number) does not add horsepower. It increases your performance by reducing engine work. It will increase quickness and reduce top end speed. Adding larger tires will reduce these benefits, depending on how large you go and what gear upgrade you choose. Once your tire HEIGHT and gear choice is selected, your speedometer and transmission shift points will be recovered by changing the speedometer gear in your transmission tail housing in pre-1999 F-150s.

 

Great response thanks very much. So if i have bigger tires then the calibration of the speedometer is off if i change my gears would it even out back to the right calibration or close enough anyway?

 

You're very welcome ! What you have described is the way it works, but that would take some planning and it may or may not be 4.10s. "bigger tires" is a bit vague. Once you know EXACTLY what wheel/tire combination you are going to use, you can pick the closest gear ratio to put it back to normal or change ratios totally. We're talking tire HEIGHT for the calculation. If I was going to the trouble of changing gears, I would install a set that would compensated for the tires AND further add performance. What you can do is use a online calculator to figure your tire height, figure what gears would put you back to normal, and what other combinations would be like. Here is a simple place to do this: menu on the left

http://www.ring-pinion.com/calculato...latorsind.html

 

Awesome thanks. I think for my new 33" tires i'm going to need a 3.75