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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...

1000N isn’t a massive load. Assuming a 75kg rider with a 50/50 weight distribution, it’s only 2.7g. Your 30g is probably at a much higher frequency than what would typically cause frame displacement. For your 28 vs 32h question. A frame and a wheel are essentially springs in series. Deflections would add together for greater total displacement. You can’t “use up” the force.

Great article, and it would be amazing to see rider feedback Vs each of the changes (of course run blind, with a sock over the modified parts). But it got me thinking about the front to rear balance in compliance - how does the relative stiffness to wag and roll for a fork compare to the rear - mental FEA says stiff in roll but fairly soft in wag. Would it be useful to balance both ends, and how would you do it? Machine down the axle interface to do an anti-torque-cap? Take material off the lowers around the axle?

Hey Ryan, again, awesome work, I really love this stuff, and it is why I got into using data acquisition on my bike! I read this over a few times and have some questions! Why did you decide on 1000n of force? With my data acquisition, I have recorded 30g at the rear axle of lateral force, which isn't convertible to N, but say 1 "gravity" is considered as the force of gravity on Earth, is roughly 9.8 N/kg. So, let's say I hit the max of 300n, could you run the calculations on that and see what % difference...

Amazing article, thanks a bunch!

That’s a great read, appreciate your time writing that up!