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This was a great answer, and super helpful. You can design flex into the tube set itself between the welds to help remove stress from the welds. That makes perfect sense. When I was a wee lad, we were working on the Diamondback DH frame prototype and it kept cracking at welds. The factory kept making it stiffer and stronger and it kept cracking, and we just kept chasing welds around the front triangle as they added braces or gussets (FYI THIS IS A MASSIVE OVERSIMPLIFICATION IN THE NAME OF BREVITY AND PEOPLE MUCH SMARTER AND MORE KNOWLEDGABLE THAN ME...

Hey Ryan, is there any way to run analysis or estimations of wrapping a rear end in carbon like greg minnar did on the Norco? How much wrap is needed to make a change? How m thinking about trying this on my steel rear end to mitigate some wag and wallowing feel.

I still need to find the time and find a donor frame to do my bushing bearing test to isolate rear frame flex. I'm trying to find an old Santa Cruz to do it on, less bearings so I can isolate rear end wag and roll quite easily. Add rubber bearing grommets for movement and install smaller bearings inside is the plan. Not sure how feasible it is, but won't know until we try making it happen

And hey @Ryan Burney I looked back and noticed you were working with 6061, 7075 should give a different result.

It's not that you won't, just that the stresses should be below the fatigue limit at the weldment. A well designed joint is important, a quick transition from thick to thin in an area that sees high forces might be bad if it relies on the weld joint.

I've learned a ton about welding, rivets, and metalurgy from these answers, but I'm still wondering: aren't you gonna increase the failure rate at welds by inducing additional flex in a welded aluminum structure?

I'll only speak to "boats" but riveted construction is usually limited to small jon boats (12-14' length) using thin gauge sheetmetal (1.5mm or so) construction. Welding requires higher skill and a slower manufacturing speed. Rivets are quick and low skill in comparison. That said, most small boats for rougher water use are welded these days. The type of aluminum used in the design drives the way parts are manufactured. 5052 used in marine applications has a relatively low tensile strength but is less affected by the heat from welding and has good corrosion resistance. These qualities work well for boats...

Absolutely fantastic article, thanks a lot! Such interesting findings and very well written 👌 I'm really surprised how well the cnc chainstay holds up against the tubed version. What's your prediction, would one of the solutions have more potential / have more room for optimization?

+1 for rim width. Spoke no. Could also be a size specific option. I have no problem running ex471 28 spokes over 32 ex511’s at 90kg I had 29” roval 28/20 spoke carbon rims on my enduro and they actually held up really well. I think the narrow rear thing is actually a tyre profile/roll thing as much as a stiffness thing, like there’s 20g in the difference between an ex471 and 511

Brilliant write up again Ryan. One thing I'll add, is that it's interesting that the engineering has become so good, that a lot of pros and frame builders are now looking to make frames more compliant, and that is with fancy high end suspension and light weight bikes. We really are approaching the final frontier of design.

At what point are you going to increase failures at the welds by increasing flex in a welded aluminum structure? I think that's why they use rivets instead of welds on planes and boat hulls.

Also, how much does the shape of the rear triangle make a frame prone to flex or not ? I mean, if you compare for instance a Giant Glory to an Intense M1 (moreover the high pivot one) or a V10, doesn't the shape of those 2 bikes is more prone to flex because the triangle is way more compact tha nthe glory ? To explain better, let's compare a similar set up, that of a Santa Cruz Hightower for instance (or most SC), and that of a Scor. They're quite similar, both are VPP, except the SC has the...

@Ryan Burney thanks for the write up! Excited to get going with the build, will be sure to write an update once I get to test everything over the summer. For context, I weigh 220lbs and generally prefer a stiffer bike. Im curious to see what a 10% vs ~100% difference in compliance feels like on trail. Eventually I’d like to have a set of replaceable stays to adjust frame compliance for particular tracks/conditions which would be a more minor change. Then if I need to make a significant adjustment (if I were to build a frame for someone much...