Stiffness versus Compliance

Frame stiff but maybe the chainstay compliant, wheels compliant radially yet stiff laterally. Stem stiff, bars compliant but then only in one plane if you line up very faded little marks. Seat post stiff, but compliant seat. Fork stiff fore-aft, yet compliant in some other direction for better tracking. Hub should have instant engagement, except while rolling at which time they should have decidedly poor engagement. That should do it, the perfect bike if you will (wheel?).

Oh yah, add compliant radial tires.

Personally I feel that most frames are overbuilt and too rigid for the average rider.  After watching in person the pros at MSA, it’s clear that the forces they are putting into the bike are absolutely unreal.  So a frame to a top 30 rider I can understand why they get to that stiffness level to give them the support they need.  

I’m a believer in that we should have a consumer spec and race spec. Right now, the Commencal Supreme V5, Frameworks and Atherton are riding the fine line of what feels good to a consumer yet can deliver  support to their top pro athletes(if they are in fact on a production frame).

Not sure how we got to this point where everything is so stiff. But I’m happy things are moving towards a more compliant and less of a teeth rattling ride.

Carbon wheels have come a long way and wayyy over built when they first came on the market. Check out this from Enve new rims and Crank Bros, things are definitely going in a better direction for consumers.

Another area that can help the ride feel that I think is really over looked is spoke diameter and tension.

 But the biggest area for improvement in my opinion that is needed is frame compliance, everything is a bandaid fix for stiff chassis. Personally I’ve never rode a bike with a front end that is too soft, rear end yes.

Such a tricky thing, right?

I've noticed that in my constantly loose terrain with poor traction, that the more noodle like a bike is, the better it seems to work.

Someday, we'll be 3D printing our custom frames with custom geo, leverage ratios & even frame layup.

One thing I think we ought to note here is we have so many methods of tuning stiffness and compliance. Some are cheap and easy, others are expensive and difficult. 

What I'd wager we start to see, for those who are actually good enough/ride enough to care about this, is most end up tuning compliance through the handlebar, wheel and even fork (38 vs 36 etc), but frame stiffness is usually left alone. That will suffice for 98% of riders.

That said, manufacturers have already recognized compliance in the rear end of the bike makes for a better riding bike if done correctly, so we'll see a little acknowledgement of this, too. I'm just a much bigger believer you can get more flex out of a wheel than almost any other part, if you so desire.

It depends so much on the rider, their weight, the trails they're riding, etc.

I've ridden wheels in the desert that felt great, only to ride them in the pacific northwest and finding them to be noticeably flexy.  You can put a lot more lateral load on a wheel when you're hooking up hard in grippy loam.  I think vertical compliance matters more in rocky, sandy places, and lateral stiffness matters more in loamy, grippy places.

I've ridden frames that felt solid and precise on flowy jump lines, only to find that they're overly stiff and get chattered off the line in chunky, rooty terrain.  But I'm not a huge guy, so I could see that frame being perfect for someone who weighs 50 lbs more than me.  And the frame that I'm riding that has goldilocks levels of stiffness and feels just right for me maybe feels like a wet noodle for a big guy.  

I've ridden bars that I think feel great - they're precise, and my hands feel fine.  But other people ride those same bars and say they're brutally stiff.  I think different people are sensitive to different frequencies.

Which is all to say, I don't think there's a universally correct answer.  Different people in different places will want different things, and they're all correct.

The engineers know far more than I do, so I'll take their word that the compliance is in the right ballpark. I'm not much of a test rider anyway; the only flex I can ever feel is when I try to push a Harley-Davidson into a parking spot and the steel handlebars flex about an inch and a half. 😅

I'm sure there's a rider weight factor in this, too. Lighter guys like me don't always flex things as much, perhaps. 
From a philosophical standpoint, I'd argue that zero flex anywhere is ideal, but of course that's not true. 

"How is compliance quantified?"

Whichever best fits your marketing requirements.

I’ve tried 28h front and rear aluminum rims with thin spokes to negate a stiff frame and I didn't like the feel, it was too wobbly in corners. I think there needs to a compromise of both.  

Ya know the first step is understanding there is a problem. Hopefully this thead will make riders start to think about their bike setup choices.

For example, I was riding a bike park last weekend and a friend hands were going numb by the bottom of the run. I look at his bike and notice 20mm rise bars, straight gauge stiff spokes, too much air in tires, full carbon frame.  I definitely won’t lie and sometimes it’s riders fitness is the cause but giving yourself the last mechanical advantage will only help.

There is a podcast on Bike And Big Ideas with the guy from Enve. They are just comparing to it’s previous model. I think it’s in a rig with rim only.

https://podcasts.apple.com/us/podcast/bikes-big-ideas/id1461144682?i=10…

It's really all relative to how much you weigh and how hard you ride. Both of these factors put more force into a frame and require more stiffness to compensate. I have a light friend who can get away with 24 spoke wheels and lighter casing tires, at 220lbs on an XL frame, I put very different stresses on the bike than he does and have very different requirements from my equipment.

I think we could figure out some type of compliance scale based on these factors below.

Rider weight: 

125lb more compliance needed.

250lb less compliance needed.

Rider ability:

Beginner rider could use a softer setup.

Pro rider could push a stiffer setup harder.

Riding style: 

Playful park rider could use a stiffer setup(but not always).

Downhill/enduro smashing into rocks and off chamber could use a softer setup.

Dirt type (grip): 

Dry dirt/hardpack could use more compliance for extra grip.

Tacky dirt, clay, loam can run stiffer setup.