# EN 14766 Safety Regulation for Frame Design



## carpio77b (Sep 11, 2011)

I just read most of EN 14766 Safety Regulation for Mountain Bikes. Seems like the testing requirements would be prohibitive cost-wise for a one man custom frame builder. It got me to thinking whether custom frame builders perform calculations to determine size/thickness of structural tubing or just go by experience for buyer's weight and riding style. If calc.s are performed, how detailed are they and are we talking manual or computer models?

Also, do frame builder's perform NDE on the welds to verify weld quality or just visual.

The testing requirements in EN 14766 show what the engineers who wrote the standard viewed as the most "safety related" loads that a mountain bike sees, but as a rider I'm interested to know how frame designs address these loads to put strength and stiffness in areas where they are needed and/or desirable for ride quality. The curiosity comes from reading alot of discussions about frame materials and frame designs being more compliant, springy, noodly, flexy. Since I've only owned (4) mountain bikes (2) hardtails and (2) FS, my experience with various frames is limited so I'm not quite sure what the terms above mean as I notice a slight flexiness in my steel hardtail along with a perceived damped and more comfortable ride quality as compared to a past aluminum hardtail (Steel frame is a 29er with tubeless low psi tires, while Alu. frame was a 26er with tubes and higher psi, so comparison may be skewed)

FWIW, the interest in EN 14766 came from the cert. label on my Inbred 29er.

Any commentary from frame builders would be appreciated:thumbsup:


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## Walt (Jan 23, 2004)

It is just done based on experience. Doing a full FEA or whatever on each new custom frame would be A) a lot of effort/time/money and B) a bit of a waste of time given the LONG history of this basic (safety bicycle) design and the subjective nature of things like "flexy" once a human rider is involved. 

-Walt


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## Drew Diller (Jan 4, 2010)

From a former software developer's perspective, what was told to me by the benchmarking numbers didn't always tell me everything about the frame rate I would actually get on screen.

I'm glad to see that this translates into frame building, as I was hoping it would.


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## AndrwSwitch (Nov 8, 2007)

A shape like a bicycle, especially a safety bike, is actually pretty determinate. I bet a limited number of load cases and Excel would be enough.

FEA kicks in when shapes get weird and load paths get uncertain.

OP, with all due respect, your comparison blows. BSNYC once compared trying to judge the ride quality of a bike frame (road) to trying to say something about the springiness of a floor by jumping up and down on a rickety table standing on it while wearing running shoes. I think that goes double, or maybe four times as much, for mountain bikes. If your wheels couldn't give you a smoother ride when you throw a larger diameter and lower pressure at them, would that be okay with you?

A lot of higher-end frames are optimized. Or at least, their manufacturers shout from the heavens that they are and have colorful screenshots from FEA to show it. And now that I'm in a job where they pay me to design things someone will fabricate in steel and I'll subject to twice their maximum load and I have access to FEA, I pretty much always do at least a little bit. If it doesn't come out how I expected, something's wrong.

Structures can certainly be designed for different strength and stiffness characteristics. And they are. I just don't think I can feel it past all the deflection in my tires, wheels and suspension.

I bumped into an interesting article about that the other day. In blind testing, riders couldn't say much of anything about the bikes they rode. Some, who trained a lot and had access to a power meter or speedometer during the test, could tell when they were on something more aero. The biggest difference manufacturers could create between a stiff bike and a smooth bike was about like a 4 psi change in a road tire - something inflated to about 90.

Kind of like the expensive wine effect, really.


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## BenCooper (Feb 25, 2013)

I think it was Mike Burrows who once gave a bunch of plain unbranded frames to a bunch of bike journalists - some he told them it was a steep and twitchy frame, some that it was relaxed and comfy. The journalists agreed about the differences between the frames.

The frames were actually identical.


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## dr.welby (Jan 6, 2004)

BenCooper said:


> I think it was Mike Burrows who once gave a bunch of plain unbranded frames to a bunch of bike journalists - some he told them it was a steep and twitchy frame, some that it was relaxed and comfy. The journalists agreed about the differences between the frames.


On the other hand, you have the Bicycle Quarterly tests where the testers (who preferred flexy frames) had no problem figuring out the more flexible frame in blind A/A/B testing.

There was a also a test in Bicycle Guide in the late 80s where they built up a dozen identical Marinoni frames, all with different tubesets. They then had a bunch of people test them and rank them. One of the most popular frames was built from one the cheapest tubesets.


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## Eric Malcolm (Dec 18, 2011)

To the OP, without getting really technical or geeky, I would suggest you go out and diversify your ride experiences of bikes, ride old school early variants, contemporary bikes, road bikes, CX as well as your MTB. This will widen your understanding of a frames 'feel'. The Diamond safety frame was essentially based around 1" TT and 1 1/8" DT and ST for decades. So proven, that the design is unquestioned, and I have never seen a design tech formulae for the bicycle. I do variations of cycle designs, but at the end of the day, variations are simply that, variations of a proven design. I work with deflection loads and moments of inertia. The issues I look at relate to meeting equivalent stresses of a given tube to what I choose to replace it with. For example, if I select a DT of 35mm with a .9mm wall that is 650mm long, but add a triangulation to the design that has another tube intersecting it approximately 3/4 along it length up from the BB, as a free span I now have 487mm that can deflect. The other 25% is a very small triangle and not likely to be able to deflect, so I have a stiffer frame or I reduce the Diameter of the DT to restore 'Flex' if I want some. It gets complicated yes, but that's why I experiment. Maybe someone could come up with a high tech computer modelling thingy, but it would destroy my fun. I need to dream......

Eric


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## BungedUP (Aug 18, 2003)

In my experience, the 2 companies I worked for (16-45 employees, depending on date) found testing frames at even a VERY rudimentary level very expensive _culturally_. By that I mean that regardless of whether or not it was economically expensive, the idea of testing was deemed to be very expensive from a labor time & materials cost : benefit, and so only done either rarely, or when absolutely necessary for one reason or another. Even when it was suggested internally, it was rarely performed. I personally took on destruction testing on occasion, but these types of tests were usually brute force tests, involving hammers, levers, and the like. I did once make a testing machine for rapidly cycling cable through a newly designed plastic cable guide for tandems, but I took that on in my own time largely (I was not paid for it), though the company benefited from it.

At one of the places, we sent a small number of frames to be tested to CEN standards. It was interesting to see the results, but in the end, the company used it as a one-time educational tool, and not used as a benchmark to continue testing against (at least while I was there). The standards appeared to be extremely difficult to pass. If the mountain bike standards are similar to the road standards (I'm not entirely sure what the standard for testing was other then "CEN"), then I'd be willing to bet that many very well made frames, which should largely be regarded as safe to ride, would not pass, even made by the best of custom builders, and even if they spent significant time calculating forces that they expected to be applied to the structure.

Frame standards ARE interesting, and they are useful. They are not always necessary, nor are they perceived as "cheap" for small companies. The interest in scientific pursuit, the desire for increased structural integrity (regardless if it exceeds what forces a frame is LIKELY to receive), and the budget to perform this type of testing is necessary for it to occur. Smallish builders are unlikely to have all three of these criteria. But we can still LEARN from those that do go through these types of testing regimes.


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## woody74 (Apr 6, 2004)

Testing isn't that expensive. You can get it done for around £200 her frame by Bureau Veritas.

Bicycles Compliance Services


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## unterhausen (Sep 28, 2008)

since I have an advanced degree in mechanical engineering, I have given thought to analysis and testing of frames. Then a colleague pointed out that it would be a curse, building in extra liability where there was only a little before. So I really haven't looked into it any more than that. Bicycle structures generally have fairly small safety margins in fatigue. And a lot of fatigue problems don't really show up in fea, they are more problems of execution. So if I build using generally accepted designs and good technique, I'm not going to have a lot to worry about


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## carpio77b (Sep 11, 2011)

Unterhausen,

Doesn't the testing standard shift some liability to the independent inspection agency/insurer?
Are you saying that most bicycles (steel) are designed for stress near or above the fatigue limit? Also, your second comment referring to execution implies weld quality as the source of failure. I suppose ultrasonic testing of the welds may be impractical due to geometry.


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## unterhausen (Sep 28, 2008)

first off, most frames have not been designed to any stress limits. My comment about safety margin is related to the failures I have seen. I don't know anything about weld inspections. My work with ultrasound hasn't gone into that aspect. It seems like it should be a little tricky to get decent ultrasonic measurements on something as thin as a bicycle tube -- I'll have to try it.

As far as shifting liability, it seems to me that is not really effective for a sole proprietor builder. If a company is building a lot of frames that are the same, some testing and analysis makes sense. But really, not going crazy with design elements gives a builder a lot more useful information than testing and fea


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## carpio77b (Sep 11, 2011)

The tube wall can definitely be UT'd. Was referring to difficulty to get meaningful results with UT of the welds as these are the failure locations. The questions in this post are more applicable to the big brand bike companies who have the bucks for stress design analysis, optimization and testing.


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