Originally Posted by MWValley
Tom, Every adventure story I ever read in print, like Odyssey to Ushuaia, goes into great length over and over about how often their luggage racks cracked and failed on "independently sided" racking systems. It would seem there's got to be a connection between the two sides. Could part of the connection between the two sides be somehow a fusible link? You know something rigid enough to connect the two sides in daily use but deliberately weak enough to shear under the right circumstances?
Jeff, I appreciate the input! It's what drives me to constantly re-evaluate and improve my products.
In Odyssey to Ushuaia, I would love to know more about their luggage and what type of racks and what materials were used. When it comes to rack cracking and failure, I think that the materials and the type of frame connections come into play here. Tubular sections that have been flattened, bent and drilled out to make a connector are prone to flex cracking. A tube welded to a flat bar is stronger and less apt to flex.
What kind of adventure would it be if the racks didn't break anyway? How many adventurers have had to have a broken rack welded by a burly Vodka swilling Cossack in the black fly infested wilds of Siberia and then are invited to the local biker club for more Vodka, pretty girls and shashlik? We love to read about that stuff!
I have given this a lot of thought, and I think tying the racks together would be beneficial in some cases, on bikes with steel-sub frames and hard side cases, I think it would be an asset. A fusible link is a neat idea, but might be prone to flexing and failure? I would like to make some prototypes to test that out.
On bikes with aluminum sub-frames I'm not so sure. I recently made a set of the "independent" type side racks for a DRZ-E that had previously taken a tumble and the sub-frame was already pretty twisted from an impact on the left side. I had to straighten it out some to get the new racks to fit correctly. I wonder if the damage would have been worse if it had a box structure connected to it at the time. I've been trying to keep the DRZ-E rack system as light as possible, but I will however develop a cross brace for those that feel they might need it!
Personally, I would never put hard cases on anything that I ride off road.
Soft luggage is lighter, absorbs impacts and is safer for the rider's limbs too.
Originally Posted by Canuman
Tom and I had some deep conversations on this topic in the design phase. I was initially pretty firm on connecting them. I've come around to Tom's way of thinking now. For one, I think that many rack problems have to do with the nature of baggage people run on them. I once lusted for big, hard cases. I have them on other bikes. I will never run them off-road again. Soft bags are much more forgiving than hard cases in a fall. I've never come even close to losing one on the rough stuff. I cannot say that for hard cases. I just did a 3500 mile mixed-surface tour on my KLR with Wolfman expedition bags. I had zero problems. At times, I wished for greater capacity, but I'm glad I had to pack somewhat frugally. Extra weight was not my friend in the tough stuff.
I think that hard cases also tend to transfer harmonics to racks in a much different way. The soft bags really can't develop much of a resonant frequency, while most hard cases do at some point. It's the resonance as much as anything that leads to cracking.
That being said, it would be a relatively simple thing to add a rear loop. If Tom decides to offer one, I suggest it be an optional extra, which could be unbolted if not needed.
That's some brilliant thinking Tim. I believe you're right about the resonant harmonics having a lot to do with stress cracking. It just makes a lot of sense.