Shajota said:
AndyW said:
and dodgy... :
Well, we're not all miners that can buy anything new and flashy on offer :-*
Peter, I hope you don't mind a bit of constructive criticism. Here's an engineering assessment.
I'm afraid I agree with Andy. It looks about as dodgy as the racks from that ?spurious peddler of racks-to-order?. Definitely not as good as it could be. It actually looks like an original grab handle with a rack welded onto it. The tube wall of those grab handles is not thick enough to support any kind of load on the rack.
It's good that you've taken the diagonal brace right back to the indicator mounting point, but not so good that you've significantly weakened that diagonal brace by putting a bend in the middle. I'll give your rack a score of 6 out of 10, and that's only because the welds look neat
That rack may work for a time, but
will eventually fail because of insufficient strength at the rear mount, where the bending load is highest. If you bolt it to the bike, then lean on it with your body weight, it'll probably fold at the rear mounts. It's basically a cantilever beam from that point back to where the load is carried. Even with small luggage loads, fatigue will get to it eventually.
If you use it like it is, one day you?ll turn up to a rally and your camping gear will be gone. All that will be left is a couple of bits of broken tube. If you're lucky, you?ll hear it go because the indicator wires will hold it long enough for it to clatter against the mudguard as it departs.
Failures can be avoided by using a much thicker-walled tube for the base loop (eg: water pipe) or by adding some reinforcing around that point (the root of the cantilever).
As you've already made it from thin-walled tube, additional reinforcing seems the simplest way forward.
If it's for a 3C which doesn't have a hinged seat, you could simply add a diagonal brace from the top of the grab handle loop back to the forward mount where it bolts to the shock absorber mount.
If it's a 3CL with hinged seat that precludes bracing above the grab-handle loop, I?ve re-attached your picture showing some suggested bracing below the existing grab handle tube. Use some more of your tube to make up a lower frame member and brace it back to the upper tube with some gussets. If you use flat plate (aligned along the tube, not across) for the gussets, they'll provide additional stiffness. The indicator mount can be incorporated in a gusset. The lower tube will be in compression load. Therefore any bends (such as below the indicator mount) will need to be tied back to the rest of the structure to create triangulation and prevent buckling. You?ll also need to reinforce the mounting lug where it bolts to the rear of the frame as shown in the sectional sketch. It?s OK as a mount for a grab rail, but inadequate for a luggage rack.
Some hooks for tie-down straps might also be useful.
By the way, mines nice and strong......................
