i have a 98 f150 4x2 with a 4.2 i put lightning wheels on it and now iv noticed that when im in overdrive im bogging down the motor what size gears should i get to correct this the size of the tires is 285/60/18.

 

Pick up the current July issue of Four Wheeler magazine. It contains a few different articles and math formulas dealing with gears and gear ratios.

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98 5.4L, 4" Rancho Suspension with 33" BFG on 16" Weld Racing Rims, Chrome Brush Guard, Stainless Stell Steps, Alpine Stereo with 4 5X7 MB Quards run by an Alpine approx. 400 watt amp and 4 He2 Rockford's 10" subs run by a 800 watt Rockford amp, and CB and Scanner

 

tell me what tire size was on your truck plus current rear axle ratio and if it's a manual or auto trans. I can tell you what ratio you need after you provide this info. Also, what brand of tire came off the truck and what brand went back on?

 

the tire size that was on the truck was 235/70/16 firestone ht the tires i have are toyo proxes also its an auto trans with a 3.08 gear

 

Below is a what you can expect with different ratios.

As built - 1417 rpm at 55 mph
Current - 1306 rpm at 55 mph
3.31 - 1403 rpm at 55 mph
3.55 - 1505 rpm at 55 mph
3.73 - 1582 rpm at 55 mph

This is with trans in OD and converter locked.

[This message has been edited by Rob_NC (edited 06-19-2001).]

 

so i should i be alright with the 3.55 then?

 

3.55 should be perfect. That's what my truck has and the only diff. between mine and yours is my tires turn 3 revs per mile less than yours do. My truck is also a 4.2L auto trans.

 

Hey I wanted to give my input opn this, You may want to talk to other people on this board who have done gear swaps with the size tire you have your truck would probably get better milage and be much quicker if you went with the 3.73's or 4.10's...Just my .02

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1997 BLACK ORP EX-Cab
4.6l Auto 3.55ls
K & N
Towing Package
Gibson single 3" out rear
Eddelbrock IAS Performers
BFG AT KO's 285/70/16
Bed Extender

 

I have 3:55 in my STX with 17" wheels, and I have no problem getting out of a jam, but I think it would do much bettter with 3:73 to give that extra torque we all need. That's what I hope to go to when I get my 20's.

 

thanks for the help i've been asking other people and they said 3.55 would be ok but to go with a 3.73. now the quesr is where and how much to get the gear and install it.