Arisley
Moderator
Only because what I read doesn't make sense.
I don't think roller bearings reduce stress on a shaft by any amount. They do reduce torque to turn the shaft, and maybe that's what you mean. If the torque to turn is lower it doesn't mean the shaft has less stress. It means the rear axle gets the few extra lb-ft of torque. The shaft still sees the exact same amount
As shown above if the torque to turn the shaft is lower, it just means more torque at the other end of the shaft. The shaft sees the exact same stress either way.
Because it wasn't worth the cost. It adds quite a bit of cost to the transmission for a benefit that is too small to ever be measured. Maybe at extremely high torques it makes sense. I never tested a trans at those levels.
When you're building a several thousand dollar custom transmission you can afford to put roller bearings in. When you have hundreds of thousands of these built every year adding that type of cost adds millions of dollars, and there isn't enough benefit that anyone could actually measure it.
While I agree with everything you said. If you are saving torque, is that not because you are reducing friction? If you reduce friction, do you not reduce heat? If you reduce heat, do you not increase the life span of both the bearing/bushing and the shaft?
Not arguing, just adding to the discussion.