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OK, I will go through the case for doing it one more time and then STFU for good.
Residential ladders are required to hold 225 lbs. Who knows what Thor designed this ladder for but anything less than that standard would be irresponsible. Steel structures are required to have at least a 2:1 safety factor before failing, ie you can load it to 450 lbs before something breaks, including the attachment screws.
The spare tire and wheel weigh 60 lbs, less than a third of the 225 lb nominal design load. Also the tire is mounted squeezed against the ladder with much of the load carried by top and bottom. When a 225 lb person climbs the ladder his body mass is about twice as far off and it can be concentrated in one place, a single rung.
When you hit a bump yes you get an impact load but that is less than 1 g. Has anyone been lifted off of their seat when you hit a bump? No, so it is less than 1 g. Also in my past life we designed very big loads to be moved on huge trailers. The design standard was 2 g vertical down and 1 g up.
So that tire worst case might apply 120 lbs of down force and zero lbs of up force out of a design load of 225 lbs. I don't think it will let go.
And if it does it is very unlikely to be catastrophic. I will just see some screws pulled loose. There are eight attachment flanges with 4 screws each that would have to fail including the top pair that bolt down to the top of the roof. I have now traveled almost 2,000 miles and have hit some horrible bumps and pot holes and nothing has happened.
Now lets look at the alternatives:
The best I saw was fitting a couple of cross members underneath and in front of the bumper. But that space is now filled with a mess of wiring. Maybe I could straighten it out and move it so it wasn't in the way but it doesn't look easy.
The other way is a bumper mounted spare tire carrier. Simple and easy unless you want to get to the aft hatch which we need to do to store camp chairs and a fire pit. That would mean unscrewing and removing the 60 lb tire every time we camp. Maybe there are tilt down hitch mounts that would work, but they would need to clear the hatch cover.
So I am willing to take the risk, watch the ladder attachments for failure, but I expect it to work out fine. So far it has. Oh and btw if it does fail, I will just install some wide mounting plates to distribute the load.
David
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