Rear bumper weight capacity

[Dave W]

Just a thought to consider when you decide the rear bumper is strong enough (and after Keystone said no) is that whatever you put there is not a static load but a dynamic (live) load. That is an 85 pound wheel and bracket load do not remain at 85 pounds except while you are at a standstill. That dynamic load changes from that 85 pounds down to zero at the top or bottom of a road bump then reverses itself and accelerates until it reaches the opposite point. An easy example is that paddle with a ball on a length of rubber. Whang it and you don't feel a thing until it stops. You then feel that load. Miss the return, you don't feel that either until it bounces back.



In other words, that bumper is being subjected to load - unload-load again and again over the miles.

[DebNJim B]

Originally Posted by Dave W

Just a thought to consider when you decide the rear bumper is strong enough (and after Keystone said no) is that whatever you put there is not a static load but a dynamic (live) load. That is an 85 pound wheel and bracket load do not remain at 85 pounds except while you are at a standstill. That dynamic load changes from that 85 pounds down to zero at the top or bottom of a road bump then reverses itself and accelerates until it reaches the opposite point. An easy example is that paddle with a ball on a length of rubber. Whang it and you don't feel a thing until it stops. You then feel that load. Miss the return, you don't feel that either until it bounces back.



In other words, that bumper is being subjected to load - unload-load again and again over the miles.

Good point. My manufacturing experience as I recall tells me that dynamic load saftey factor is 10to1. So that bumper needs to withstand an 850# load for a bouncing spare.