Lift kit, rims/tires, and gearing

[sobelizelixir]

Alright, I have searched for about 2 weeks now trying to find answers. Here is my situation.

I have a 2002 7.3 F250 crew cab short bed. I want to get new KMC rockstar rims and toyo tires. I found a nice package deal on ebay of 20x10 10mm offset rims with 35x12.5R20 Open Country M/T tires.

Now, all I have on my truck is a tuff country add-a-leaf kit which provides 1.5 inches of lift. Other than this everything else is stock. I am pretty sure that with my current height I cannot fit these rims and tires. Is this correct?

If I cannot currently fit these on my truck than what must I do in order to have them put on without any rubbing? Will I need a 2", 2.5", 4, or 4.5" lift? I like the current height of my truck and don't want to raise it much higher. Can I get away with a leveling kit and some trimming?

Finally, I have the 3.73 limited slip gearing. Is it okay to run these rims and tires without to much damage to the transmission? I know the 4r100's suck so the last thing I wanna do is put more wear and tear on it.

If I am better off switching the gearing I am going to go with the 4.10 ratio. I dont tow and this is my daily driver so I would like to have it be in-between powerful and good MPG. If I switch, do I only replace the rings and pinons? Is there anything else that needs to be swapped out?

Thanks in advance.

[SmokeyWren]

Originally Posted by sobelizelixir

Finally, I have the 3.73 limited slip gearing. Is it okay to run these rims and tires without to much damage to the transmission? I know the 4r100's suck so the last thing I wanna do is put more wear and tear on it.

Tire size doesn't have anything to do with damaging a 4R100 tranny. If you keep good ATF in it, and never allow it to get too hot, and calibrate the speedo so you have stock shift points, then that's as good as you can do. Working the tranny will not hurt it as long as you don't do juvenile things such as drag race or jerk the tranny with sudden pedal to the metal movements.

The 35" tires will change your effective axle ratio by 8.4 percent. Or your 3.73 will "feel like" a 3.42. If you don't tow or use the truck as a truck, then you'll probably like the stock axle ratio combined with the big tires just fine.

The longer legs should increase MPG, but the wider and taller feet will decrease MPG more than that because of the increased mechanical and aero drag. So as a result you're going to lose a coupla MPG with the bigfoot tires, regardless of your rear end ratio.

If I am better off switching the gearing I am going to go with the 4.10 ratio. I dont tow and this is my daily driver so I would like to have it be in-between powerful and good MPG.

Drive the truck with the stock ratio and big tires for a month or so to see if you like that combo. But if you want to get back the power you felt with the stock tires (at the cost of even more loss of MPG) , then you need a 4.10 ratio. The 4.10 is ten percent shorter than the 3.73. You need 8.4 percent because of the increased diameter of the tires, plus you need more than the other 1.6 percent to make up for the increased drag of the bigger feet. So 4.10 should get you back to almost the feel of the 3.73 ratio with stock tires.

More than a 4.10 ratio is only for increased acceleration and only if you understand it's going to cost you in even worse MPG. But lots of folks with 35s love their 4.30 ratio because it gives them a leg up for the stop light grand prix.

If I switch, do I only replace the rings and pinons? Is there anything else that needs to be swapped out?

Not my area of expertise, but I understand that if your change is from 3.73 to 4.10, all you do is change the ring gear and pinion. You can get the parts you need from
Randy's Ring & Pinion. The Differential Experts. Auto Parts & Services.
but don't even think about doing the work yourself unless you have lots of differential fixin' experience.

[sobelizelixir]

awesome post smokey. Thanks for your time. Ill probably leave the gearing at 3.73 until I get enough money to buy somethin worth towin.

Now that the gearing has been solved, can anyone chime in on my issue with the rims and tires? Will they fit? and if not whats the minimum lift height?