Join Date: Mar 2000
Location: Eureka IL
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Re: Drunken Gear Ratio Torque Physics Question
well theres a lot of stuff at play in these types of situations.
the reason a U joint sees more torwue after a gear reduction is that a gear reduction works as a torque multiplier. If you engine has 100ft/lbs of torque, and your first gear is 4:1....then at the output of your tranny you can measure 400 ft lbs of torque....neglecting the friction of gears and other loses. that means that any component after the gear reduction will see 4 times the load as before the reduction. this is why we never really have to worry about beefing up the output shaft of the engine.....unless we run insane amounts of power theres no need to worry, we just build up the drive train to handle the insane gear reductions
the reason a guy with higher gears blow Ujoints is because of the dynamic loads on his drivetrain.....this is how i managed to Explode a D35 with a stock 4 banger. spinning the tires, spinning the tires...then they suddenly caught....Blamo! no more d35...i dont miss it.
The U joint in your driveline thats the most vulnerable assuming they are all the same size, would depend on the ratio of your gearing to your tire size. A big tire, as we all know, cancles out the effect of the low gearing in your differential as far as torque applied to the ground is concerned
let pretend we have 2 jeeps with identical drive trains....except one has portal axles for a total of 4:1 gear reduction (2:1 in the Dif, and 2:1 in the portal) in the axle....and the other has a regular axle for a total of 4:1 reduction in axle dif .....both axles have same size shafts etc.........if we had a situation where the tire was NOT MOVING...no slip at all....frozen in mud from getting stuck last night..... and you gassed it realllllly hard and then let go of the clutch (no clutch slip...this is a perfect world). the portal axle ujoint would have a better chance of living than the U joint on the normal axle. because it will see half the torque that the conventional axles ujoint will.
in my crazy lil engineering world the axle U joints have to be tougher. but by how much depends on the tire size and all that