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Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending). Strongly disagree on layup effects being marginal though. I know for a fact layup can influence the stiffness to the tune of 5x from the same mould. Granted, what I'm talking about is making things softer, not stiffer, which is a different problem altogether as making a small diameter tube into a rod by filling it in still won't get you to the point that taking a larger diameter tube would stiffness wise, but still. Layup can have an immense factor...

With carbon why not just adapt the layup along the tube?

Bringing this back to the top. Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal has been on the rectangle tubing and it’s a great ride feel!

We did try the full brace vs "bowtie" / "butterfly" brace but there was no noticeable change to the rider feel, I didn't run the numbers but it didn't seem like a big difference at the time. I'm going to make another that is super thin to hopefully allow torsional movement but still hold the structure together so it's not completely free. I think these brace options are great when you encounter different types of soils and grip levels. Currently, in Southern California, it's super dry and hardpack, so as much mechanical grip that we have is an advantage, but...

I remember being told when the Druid V2 came out that Forbidden is already using this standard and that looks to be accurate.

So SRAM is taking the UDH success to brakes...? Patent Center

Well, I’m happy now that I know the modifications weren’t just a placebo effect on grip (thanks to your FEA). I think you nailed it—I wouldn’t have done anything differently. Thoughts and learnings on the mods: At the time, people were asking me if they were safe and reliable. I was confident that I was actually adding reliability by allowing the forged parts to flex and reducing stress risers near the welds (maybe that could be your next FEA project! 😉). I was careful to include large, smooth radii in the machined cuts. Danny had two bikes with these modifications...

I did a seatstay brace test last week on a full steel downhill bike. I just did a run with the brace and without. The above graphs are without the brace. This is just a visual to show the difference between rear axle to BB. To get the % change, I just the Excel files through a program and separate left and right accelerations. In this case, without the bridge, the rear axle moved laterally 6% more and had 20% more torsional twistng. The conditions were super dry so I feel that the added compliance gave me more grip and...

This is a rad article, and a really interesting discussion. Back in 2018/2019, I cut the seatstay bridge out of my Alloy Sentinel (This was the first article sample I had been riding for 1.5 years at this point). I initially did this to be able to accommodate using a 65mm stroke shock to get 160mm rear travel to experiment for what ended up being the Spire. The side effect of this was introducing a significant amount of rear wheel vertical roll. It was shocking how much it increased rear wheel traction on any type of off camber surface. ***Not...

What an awesome article! Our team rode Furys this last season and they are pretty fantastic bikes! Would the aurthor agree that. DH bikes have to be so strong that they become stiffer than necessary as apposed to trail bikes? Could this affect material choice? The wag vs roll is especially interesting to me. I feel like there are benefits to wag it terms of the tire's contact patch and along with the way the bike springs back after it's been loaded. I've heard of people referring the bike bending, or swimming when referring to wag. That could help with...

The massive problem with fork compliance is that it causes bushing bind. Go apply a mild torsional load to pretty much any MTB fork (except the EXT Vaia) and it basically stops moving. This isn’t really a problem for moto because the upper bushing is mounted on the stanchion. I believe the moving bushing is also why split clamps are a moto invention that doesn’t really do anything for a MTB. The clamps are split to allow the tube to flex more consistently and not bind as the bushing slides through it.

I do think fork compliance needs to enter the conversation once we start, reducing rigidity and increasing compliance of the rear end. I switched to the Manitou Dorado and do notice more grip off chamber than I did with a Fox 40, Boxxer(2024) and Ohlins DH38. I’ve only recorded data with the Dorado in the SynBike system, but I’ll put this on the list to test the torsional movements of forks. Fork compliance is already in the works in MotoGP with Oval fork tubes from Ohlins. The idea is a stiff platform for force while braking and compliance for lean...

Hi Ryan, Great job validating my work! It’s really cool to see the numbers backing up the theory. Ideally, we would have done the 3D modifications and FEA first, then created the frame or modifications to match. Unfortunately, that wasn’t an option as I didn’t have access to the 3D tools or enough time. The first modification was done at Val di Sole. The track was super wet and rooty, and extra frame compliance and grip were needed—that’s when the hacksaw came out 😂. However, as you mentioned, modifying the link without simultaneously addressing the seat stay bridge meant the...