What Does Stiffness Feel Like?!

Equipment
1

No, I’m not being funny, but I can hear y’all sniggering.:face_with_raised_eyebrow:

I started cycling back in '15, and since then, I’ve enjoyed absorbing roadie knowledge, learning, questioning, and discovering for myself, but one thing that still confounds me is this whole damn stiffness thing.

I’ve come to my own conclusions and opinions about many things cycling related through direct experience. Tires and tire pressure, for example. I’ve tried different brands and sizes, different pressures, different treads, and so forth, and I can say, “X tire feels like X, and Y pressure feels like Y.”

But stiffness! What IS it? What does it feel like?

I currently own and consistently ride three bikes: an aluminum grocery getter/shopping bike, an aluminum cross/gravel bike, and a carbon road bike, all with different wheels, tires, bars, stems, saddles, and groupsets. (Remember I said I like to try different components to find out for myself.)

And though each bike has its own feel, I have no idea how much stiffness comes into it. If anything, I’d say the carbon bike is the least stiff (if I had to guess), but I prefer that feel to the other bikes, which would be more stiff.

I have never been on a climb and thought, “Geeze, I wish all my power would go straight to my rear wheel, rather than stopping off at the pub first. Gawd, here I am trying to get up this hill, and a hundred of my watts are holding down a barstool somewhere.”

If I had the resources, I’d do what Jan Heine did and make a noodle bike and a rigid bike just to feel for myself, but alas.

Can y’all peeps help me here? This whole stiffness thing sounds a lot like so much marketing, and I’m irritated to no end that I still have no idea.

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A stiff frame feels sort of like leg pressing an amount of weight you can not move. I read it described a very stiff frame feels like the bike “pushing back” and your legs fatigue prior to your CV system. A frame less stiff can flex more in sync with your pedal stroke and your CV system will be taxed at a higher rate.

Sorry no citation to back this up and for dredging up an 11 month old post. Just yesterday I rode with a guy named Eric Marcotte (former US Pro road champ) who asked me how old my frame was. We both ride Factor bikes and long story short he made a statement about how much a frame can “soften up” in a couple years. To be honest, I can’t tell but, that may be because the change is so slow it’s not noticeable. Or I don’t ride hard enough or have not worn the frame as much as he has. Never-the-less the whole frame stiffness being better/worse entered my mind. Everyone seems to think stiffer is better. I honestly don’t know but, I think it depends on how the frame flexes more than how much the frame flexes.

Boom.:boom::stuck_out_tongue_winking_eye:

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I had the same question and recency to cycling as the original poster. I have two different frames, one from 2010 and another from 2018. Both carbon. There’s a difference in riding both, but I really don’t know how to explain it. And I don’t think one is “less stiff” than the other. I want to think the newer one is better because it’s more premium, newer, etc., but I don’t really know.

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I think it feels like the bike responds immediatly when putting power down. It’s fun to accelerate. It also doesn’t feel like its twisting weirdly when cornering, it just feels solid.

It’s worth mentioning that with modern frame building, especially on carbon bikes, the frame has different degrees of stiffness in different directions. With metal frames, it can be influenced by tube shape and diameter, but with carbon you can also build it in, by changing the carbon lay-up.
In general, you want the frame to be very stiff in the direction of power, but compliant enough to soak up road rattle and bumps.

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I never really got that myself, or at least entirely. Noted the lack of road buzz when switching from Al to CF. However this year I got a new horse, an S3 and it is notable. First it has more road feel. Like walking in bare feet as opposed to Nike Airs. Second it holds momentum through the corners. My old bike was more of a plush setup. Lost 2 -3 meters following others through corners. New one doesn’t. The more responsive thing is there for sure but I find that hard to distinguish from “NewBikeitis”.

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Agree on the above regarding ‘instant response’ but also a feeling that nothing is being wasted.

There is a climb near me that can be done as an all-out uphill sprint. On the stiffest bike (Track bike with carbon wheels & carbon handlebars) it feels like every ounce of energy is driving the bike forward. On the steel bike, the back wheel and frame feels like spaghetti.

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Agree on your general point. There is a similar reference climb near me that I set a PB on this year (YAY TR!). However I set it with my ‘softer bike’. The reason was that the road surface was rough (Very bad Dutch legoweg). The stiffer bike bounces over the surface and loses more effective power than the soft one. Next year: stiff bike + (me - 3kgs) + 28mm tubeless + another year of TR = see what happens.

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Thanks for the responses. I hear what you’re saying, but damn. I guess I don’t have the legs to spaghetti any of my bikes. The al grocery bike definitely feels least responsive but most stiff. The carbon roadie feels like it has a slight give under my (standing) legs, but it feels like it accelerates faster (which it does, being lighter with faster tires).

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It’s quite subtle & I’m sure there are many factors at play, including weight. The performance difference at the end of the day is also marginal.

I also thought it was marketing for years, mostly as a way to protect my wallet. This worked until someone loaned me a Cannondale Supersix Evo. I’m sure the feeling of acceleration fades with time but it was night and day different to my bike at the time.

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That’s how I feel, I wonder how many watts before this is really obvious.

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Just to amplify a bit on my experience I mentioned before. I was out for my last ride on my stiff bike yesterday before I hang it up for the winter. I was riding with some of the stronger guys in my club. I was struggling to hold wheels with them. I certainly don’t have the guns to stress any frame that much either. I hadn’t ridden it for a while because the weather had been poor here and I was using my winter/commuter. Holding on to these guys wheels meant I had to gun the corners. It became really clear what a stiffer frame meant at those points. Yesterday I was able to throw the bike over quicker and to get on the power earlier and earlier as I adjusted to the bike. If I tried that with my #2 I would understeer and drift out. You could feel the stiffer bike dig into the turn more.

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Question for those who have been in the sport a while or engineers…I once read something on how a bike “planes” is more important than “stiffness”. What I don’t recall is if this planing was in reference to alloy bikes or both carbon and alloy. Anyone have any info about planing and a carbon bike? Just interested…

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Oops. I hit the wrong respond button. So here again is the article on planing.

1 Like
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Not sure if this planing thing is necessary. Strain is a simple engineering concept. If you put a force on something it stretches like a spring. Everything does this. Stiffer things just move less. That’s strain. So just like a spring we can talk about strain energy. The amount of energy that is in a stretched spring. Like an old wound clock. Power is simply the application of energy over a period of time. So if something is less stiff it has the capacity to move more and store some of that energy. In the case of a bike that is energy coming from you that isn’t going to the road. It is being stored in the frame and released as you come out of the power phase of your pedal stroke. That motion is lateral to the bike motion so is essentially dissipated and lost. A stiffer bike will dissipate less.

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GCN did a video on this.

Heine’s look into planing is as close to sciencing this topic I’ve seen, and if I recall, the “plane-ier” bike was faster, but at a higher power output.

I’ve watched videos, read articles, perused viewpoints in forums, but I wanna feel for myself. Since I’m not a racer, I’d gravitate towards the bike that has my special blend of responsiveness and compliance, and I’m just curious to know how much “stiffness” factors in to my special blend. Anyone have a couple dozen bikes I can ride one after the other? :rofl:

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I’ve always thought of stiffness as divided into:

  1. Fork and steer tube stiffness

  2. Front triangle

  3. Bottom bracket

  4. Rear triangle

Bottom bracket stiffness is far overrated and blabbed about. Unless you’re pro-tour level, just about any decent stock bike will have sufficient BB stifness.

Fork and steer tube stiffness really comes through when you are making the pitch into a corner, and then tracking into the apex. A wiggly fork and steer tube makes for a noodly, confidence-sapping front end. Most new bikes handle this well. Go find an '88 TVT carbon frame or a VItus 979 for an example of flexy fork and steer tube, feels like a death trap descending.

Front triangle stiffness shows in cornering, but it can be this weirdly disconcerting feeling of the fork being planted and tracking the bike well through the turn, but the top tube being wiggly and, as a result, the whole bike doesn’t feel confidence inspiring. I used to know the former custom designer at Litespeed. When they did the bikes for Lotto, the company overrode his top tube thickness specs and instead made the lightest possible bike. The Lotto guys could flick the TT with their forefinger and get the bikes to wiggle/shimmy. Tchmil rode a repainted Colnago in the races that mattered to him. Most bikes are fine here as well – in fact, modern top tubes may be a bit overbuilt.

Rear triangle – how “planted” does the back end feel?

Bikes are so much better now than they were twenty or thirty or forty years ago it’s almost laughable. Any modern carbon bike is more than stiff enough – in fact, most are a bit overbuilt.

1 Like
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Awesome description. Thank you.

My gravel bike definitely has a flexy fork; there’s a forward/backward mush and sproing under hard braking, and bumps feel sproingier.

I’ve heard so much about bb stiffness that I hadn’t considered the rest of the frame as you explained, and your explanation is very helpful.

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Aargh. Hit the wrong reply button again. :roll_eyes: Sorry, @RobertK.