Hello All.
I have a question about gears. I have a 1999 F150 SCab 4x4, with the 5.4L V8, 4R70W Auto Trans., 3.73LS Gears.

I have a 4" Rancho Lift kit, with new 305/70r16 tires on 16x8 wheels.

The old stock tires were 265/70r17 on 17x7 wheels i believe.

Will i have to change the gears to 4.10's now with the new wheel/tire change?

I was also told that i would need a superchip to recalibrate speedo.

Any advice on my little problems? My truck is a daily driver, with light 4 wheeling on occasions. Basically just take it hunting 2 or 3 times a year.

 

Didnt think it was that tough of a question. LOL

 

Will you have to change gears? That depends completely on you. Going to a larger tire size is usually perceived as a loss of power, due to what is effectivley a gear change to a higher ratio. Whether or not you have to change gears depends on whether or not you can live with the perceived power loss. In your case your tire change was only about a 3.8% difference, so the perceived power loss might not be significant to you...especially when compared to the cost of having both axles regeared.

Correcting your speedometer is also up to you. Assuming your speedo was dead on to start with, it should now indicate about 3.8% low. For instance, if it indicates 40mph, you would actually be going about 41.5mph, and if it indicated 70, actual would be about 72.7mph. However, the assumption that it was dead on to begin with might not be a good one. The best indicator is to check it against a GPS. If it was off just a little from the factory, it is possible that it is pretty darn close now. If it is off a little now, whether you correct it or not just depends on whether or not you can live with the error.

 

Thanks SM.

I believe i can live with the gears it has now. In doesn't seem affected hardly at all. As for the Superchip, I will prob. go ahead and get.

On a different note, I was looking at the differential cover, & noticed that the paint or cover itself was brittle at the top left side of cover. Didnt take any chances & push on it. Ordered a Mag Hy-tech cover, & praying its not to bone dry inside there before cover comes & gets replaced.