Is Re-gearing worth it?

06Fargo wrote:
So if I understand this right, if jwco5.3 could clone his truck and trailer so everything is identical except the rear ratio on #1 is 3.55 and on #2 clone rig is 4.56, #1 has no trouble keeping up in the hills, because it has the same power?

I guess it could be so if the trailer is so light it never really makes either truck lug down at full power on a grade...

OK - so then a 450hp pickup truck can hook on the same load as a 450hp class 8 Freightliner and drive away with it then, right? Same power. Gearing doesn't matter.

The issue is as pointed out, At a given speed, the engine is turning more rpm, hence the motor is producing more HP at the higher rpm, so in a sense, it is producing more HP. The thing with gearing, be it in the trans, axels, or tire diam, is one has to have the correct HP at the speed you want to go for the total weight, and frontal area wind resistance one has. If you need a total of 300 hp to go 60 mph up a 4% grade, you motor only produces 250hp, you will NEVER go 60 mph up the hill, as you are 50 hp to little.

On the other hand, if the motor produces 350 hp at say 6000 rpm, and 300 at 5000 rpm, you could, WITH the correct gearing, theoretically go 60 mph up the 4% grade, IF, you can get the motor to turn 5000+ rpm in a gear, tire diam combo, that will net you 60 mph! If you have a gear that is too slow ie say a 4.88 vs 4.56, OR fast ie taller than 4.56 for matter, you will not hit 60, you will be slow, if you gear it correctly, then you can go 60 mph.

Clear as mud eh!

marty