From my observations of hi-rise (jacked-up) trucks, there is no change in ground clearance of the transmissions. Therefore
for rough cross country driving, jacking up the suspension, etc does not protect the transmission (or am I wrong???)
No, you’re correct.
The real offroad reason for jacking the bodu is to give increased wheel clearance to fit bigger wheels / tires.
Otherwise it’s for posers. Like divers watches, even people who can’t swim wear them.
The after market in truck lifts has been making a killing by selling these kit + installation. However Scudder is right in that all these lifts do is raise clearance for THE BIG TIRES. Whitch are also making a killing selling to these asphalt 4X4 Dumdiess. Wost yet in order to lift the truck it requires to alter the suspension from it’s origonal alignment,with fabricated control arms and blocks in the rear. Thus rise the center of gravity and weakening the conection to the power train componets. As far as the transmition goes the bigger tire will effect the trans.,rear end,speedometer,clutch,drive shaft, unless proper retro fitting is done to compesate for the differance ratio. This also applies to LOWering a automobile.
Depending on your use of the word, “transmission,” you might be wrong.
The transmission (attached to the rear of the engine) is elevated by the lift (hi-rise, jack-up, whatever), and therefore “protected” from harm, but the differentials and axles are not.
The transmission may have more ground clearance, but the final drive components (differentials, axles, etc.) do not. The ground clearance for the differentials and axles is determined only by the wheel/tire combination.
Well, it’s for more than just tire clearance. The higher you get the front and rear end, the better your approach and departure angle (http://4wheeldrive.about.com/cs/tipsandtricks/g/approachangle.htm). The higher you get the frame, the less chance you have of high-centering and damaging the undercarriage. The higher you get the whole rig off the ground, the better you do in deep water crossings.
There are a lot of different styles of off-road driving. Auto manufacturers have realized that most truck and SUV drivers leave the pavement only when parking in gravel lots, so they have been reducing ground clearance and lightening suspension components, all-the-while advertising the off-road capabilities of their vehicles. Whereas “off-road” used to mean bombing along forest trails, slogging through tank traps, and maybe climbing a rocky incline, off-road now means driving on roads that are not asphalt, and doing okay in deeper-than-average snow.
For what it’s worth, I have a '72 Ford F-100 with a 4" lift, 4.11 gears front and rear, an NP205 transfer case, and 35 x 12.50 mud terrain tires. It sees about 300 miles a year and most of them are in deep mud. The lift on that truck is mainly to clear the tires, but the tires are to add lift. If I didn’t need to climb, crawl, and bog, I wouldn’t run large tires.