Mytbusting: Tubes and Ride Quality

General Discussion
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Yep, the more you dive into it the bigger the questions. As you pointed out all these things are measurable. It’s figuring out what the priority is.

Here is my rule of thumb as I alluded to. The bigger and heavier the rider the more burly you build the frame. Thicker walls and bigger diameters. For me the gold standard for a road frame is someone around 175-180cm and 65 to 70kg is going to be served well by an OS tubeset (32DT28.6TT) with mid weight seat stays. Bigger people get an XL tubeset (35DT32TT) smaller people I dop potentially to a 28.6DT28.6TT. Wall thickness adapted up or down to then tune the ride.

I generally don’t think lack of tortion stiffness in teh average frame is a problem. I’ve built a frame for a dude who was 195cm and 110kg using an XL tubeset with MAX steel fork and he loves it and says the bike tracks beautifully which would tell me the torsion value that frame is good enough.

But I get it. The designer in me wants to delve into it and really optimise the material and fea the crap out of it and really push the envelope of what’s possible. Understanding the characteristics is a big part of that.

For butted tube bending my thinking is the middle bends before the ends. That seems obvious. At a point the force reaches a level where it starts to bend the butts as well. Of course ratio between wall thickness and how long the end butts are are going to have an affect. Two tubes with the same butt tickness but with different length butts is going to have the one with longer butts having an overall stiffer dynamic if yoo were doing a weighted bending test. (needs punctuation, sorry)

Interesting to think about. :slightly_smiling_face:

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Sorry, it’s time for me to bail on the forum.

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I love this topic but man is it a head scratcher. You can assign measurable variables such as tube stiffness, torsional rigidity, weight to a frame and then state frame “A” is “X” percent stiffer than frame “B” but beyond marketing and capturing the cognitive bias of buyers who throw down a large chunk of change for a new bike/frame it can’t answer the question of what equates tubing to ride quality. I think in short this can best be compared to the analogy of Utopia, in that it can never exist because everyones view on it differs… it is fun to think about though!

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I would also add into the mix the tube stiffness calculator that Don Ferris used to have on the Anvil site.
It’s still available in Web Archive here: http://web.archive.org/web/20050215103730/http://anvilbikes.com/tubeCalc.php

Uses diameter, length, butt spec and material to calculate load and torsional deflection for a given load, comparing tubes of different spec of material, mass etc.

All the best,
Dan Chambers

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That’s a really good ‘Rule of Thumb’.
What would be the baseline for that, Walt…say 1"TT/1-1/8"ST&DT for a 140Lbs rider, or such?

All the best,
Dan Chambers

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Sorry, it’s time for me to bail on the forum.

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From what I can tell, that calculator is doing a superposition of separate butts in a beam deflection equation. pretty cool

That is an elegant rule of thumb, and I’m sure it works in 90% of cases. My only concern is that a beam’s deflection is proportional to the square of the diameter and the cubic of the length. Stepping the tube size every 50lbs is a linear relationship. That means it may be accurate enough around the nominal value but could be way far off for compact frames, or very heavy riders.

Plus, factor in the rear triangle, and I have no idea anymore!

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Sorry, it’s time for me to bail on the forum.

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Has anyone seen or heard of someone seeing the data from Columbus’s strain gauge instrumented bikes from '86? They instrumented a bike and had Felice Gimondi ride. The wiring was routed to computers in a follow car. This is from Columbus 1919 IG feed.

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Around '91 Moots built a Ti YBB softail and a couple of good cyclists, one of whom went to work for Moots, did their senior project in engineering at the School of Mines by putting strain gauges all over the frame. This was not to determine frame stiffness but to figure out the best way to build the softail. The info was very valuable and taught us that preloading the chainstays was essential.

With the frame stiffness analysis, having started Co-Motion and building frames in '88 we had a limited number of tubes to choose from. 1" TT, 1-1/8" DT, 1-1/8" ST 1" threaded steerer was a standard lugged frame. Believe it or not we also built our first tandems with a Reynolds “Jack Taylor” tandem tube set and that had 1-1/8" TTs, 1-1/8 ST and I think 1-1/4 DT. This tubeset and “triple lateral” design is the same as the tandem I rode, very heavily fully loaded, across the US in '86. Keep in mind all of these bikes had 1" threaded steerers with heavy fork blades. Not, in the least, a stiff bike. We soon starting sourcing larger diameter straight gauge 4130 and True Temper tubes in long lengths which all helped a lot.

With single bikes Dwan and I built a few lugged frames, sold them and rode them. Mostly Columbus SL tubing. When Tange came out with their Prestige tubeset and we could buy individual tubes we started to mix it up using bigger tubes, fillet brazing (until I got the guts to figure out TIG).

When I started doing Ti in '92 the tube choices were still slim and the whole aesthetic of oversized tubes was off putting to most people used to traditional road frames. I could into detail about certain tubes Ancotech was butting per Gary Helfrich’s specs, I’ll just say I have a MTB frame hanging up that weighs less than most all the Moots road frames.
Over the years I have been fortunate to have built and ridden prototypes using different tubing combinations, bb’s, headtubes. Different combos make a difference. We varied the tubesets, size specific tubing, through the sizes and line of bikes. It is often common sense. In my time steerer tubes went from 1" to 1-1/8" to tapered 1-18" - 1-3/8" or 1-1/2" (and I even built a steel MTB frame for myself with a 1-1/4" straight steerer tube). Stems and handlebars are way stiffer, carbon wheels take it to another level still. The perspective has changed as to “what is stiff”.

I will add that from experience with MTB’s the increase in HT size and stiffness and the increase in fork lengths put much more stress to the DT and TT so that the DT must be beefed up. Also from experience I have built some frames that were too light and some that could have been lighter.

I am with Walt the whole thing can be overthought, and different riders will push frames in different ways depending on riding style, preference and what they are used to. I suggest trying to ride as many different bikes as possible, understand your riding style, your size and weight as well as your preference and then go up and down from there for the rider you are building for. Always know the components constitute the vast majority of the weight and will directly influence the feel of stiffness. When stems went from forged Al Cinelli 130 long stems to Syncros welded Al it was like flipping a switch. Enough babble.

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This is very true. Once carbon became the go-to build material for frames the race for light and stiff went bonkers. Metal bike fabricators were dragged along with it since the standards changed. I see it as not trying to compete with carbon and make a stiffer bike but almost the opposite by trying to make a comfortable compliant bike with all the oversized stuff carbon has made us adopt like tapered steerer forks, oversized head tubes and large diameter tubing that people now aesthetically prefer.

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Cool article from fellow builder Rob English:

From the article:

For a given size and weight of rider I think there is a sweet spot for torsional stiffness. My testing showed me that with undersized tubes the bike rode fine until I was pushing hard on corners on a descent. Then the front end would feel a bit vague and would not inspire confidence. With oversized tubes, on rough roads the front end would skip and bounce as it tracked. But at the right size, there is sufficient stiffness for the frame not to twist much under hard rider input, but enough flex for the wheels to have a little independent tracking to preserve road-holding.

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So glad he’s on there. Hopefully the punters learn a few things.

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This is a punt! Unless we know the rider size and weight, the tubes used in all 3 frames, road conditions, and other variables like tire size and pressure, this is an empirical comment on what a particular rider prefers for torsional stiffness. There’s nothing here that describes any objective values for another builder to use to design a frame.

We do learn that there’s a sweet spot to a design; builders already know that.

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Walt-
I’ve have the same experience. I would also add that most of the carbon cross forks I have ridden (especially with tapered steertubes) are to stiff, and you end up hoping that tire pressure will save the day. Unfortunately there is less range of adjustment with those tiny tires.
Hahn Rossman

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Hello, I would like tk ask about pros / cons of lower vs higher tensil strength steel please.

For the less strong steel, would it be more compliant? EG: Columbus says for Spirit (main triangle)frame, a Zona (less strong steel) rear triangle would make it more compliant.
Marinoni also uses this config and Ira Ryan mentioned it here as well: Interview
Reynolds vaguely mentioned this with their cold worked 631 too (vs the heat treated 853)…

On the other hand, would a “super steel” like 953 be less susceptible to dent even 0.3mm at the center butt? Thank you.

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‘Compliance’ which is flex is a resultant of the tubing geometry not the material strength.

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In general all steel tubing has the same Young’s modulus of elasticity. From lowly Thron up to XCr, stiffness isn’t changed by the material (assuming tubes of same dimensions).

What some of the super steels do is allow thinner walls that still provide longevity in terms of fatigue strength and to some degree dent resistance.

Columbus (IIRC) came out with a dent resistant treatment recently (like past 15 years?!) that helps their thinner walled tubing in larger diameters resist dents better. I don’t have any experience with it.

Remember anything you see in the magazines or online sites/interviews from a frame company or tubing company is mainly marketing. It’s not the engineers talking. The engineers are in the back room cringing at what the marketing people are saying! :rofl: :rofl:

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I discuss this in my video if you haven’t seen it:

Strength is not to be confused with stiffness. All steel has the same stiffness, even mild steel.

In practice, high-end steel bike tubes are less stiff. The higher strength allows you to use thinner walls (.7-.4-.7). Usually you go up a diameter with thinner walls, so you end up roughly the same stiffness.

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sorry double post