Re: [CR]Frame Flex Testing

(Example: Component Manufacturers:Chater-Lea)

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Date: Wed, 28 Sep 2005 19:36:26 -0700
From: "Jan Heine" <>
Subject: Re: [CR]Frame Flex Testing

>Well, without going to the archives, and without getting drawn into
>a big discussion, the argument about that energy from frame flex is
>conserved because bicycles are springs is rubbish.
>Yes, deflecting a frame causes the frame to store energy. Yes, when
>the frame springs back, it releases the energy. However, this
>energy does not go back up the rider's legs, nor does it move the
>bicycle forward. It is just wasted movement.
>It often appears to me that many posters on this list seem to be
>unaware of basic principles of physics. Maybe we should start a
>physics mailing list.
>Louis Schulman
>Tampa, FL

Assuming you are correct - and who would argue with the physics - here is an easy test:

The energy that is lost due to frame flex must be turned into heat (physics!). When you ride a flexy bike on the trainer (no wind to dissipate the heat), the BB area will get quite hot. Be careful, though - it's quite a bit of energy and you could burn your fingers!

The implications of what you say are clear: On flat roads, stiffer frames are better regardless of weight. Physics also tells us that all steels have the same stiffness - the more expensive stuff has higher yield strengths, etc., which allows makers to make it thinner. But that is counterproductive - you get more flexy frames that way. So the only way to make a steel bike stiffer is to add material (or increase diameter, but within the CR timeline, that rarely was done, so we shall not consider it, lest the listmaster gets upset).

Within the CR timeline, the stiffest bikes probably are drainpipe Huffies and such, although they may be handicapped by the small tubing diameters, plus the parts weren't much good, and moderns ones are hard to fit.

So your second-best choice are the heavy and relatively cheap Japanese frames made from seamed, plain-gauge, heavy, but standard diameter tubing. Equip a frame like that with Dura-Ace 10-speed and Ksyrium wheels (the threading is BSC, so you only have to spread the rear dropouts a bit), and nobody will catch you. Even on the hills, the 2-3 lbs or so extra frame weight should be worth it, considering how much extra stiffness you get! Just leave your water bottles at home, and you'll be as light as on your carbon bike, but much stiffer!

I am looking forward to a true believer presenting us with their 19-lb. Nishiki with modern, superlight parts. Then all of us on the flexy, thin-gauge Masis, Colnagos, Cinellis and Paramounts will be left in the dust!

It's a typical example of snake-oil selling: Top-end frames that cost many times the price of bottom-line models offer far inferior performance, yet cyclists - from the pros all the way down to the poseurs - have been flocking to them, and have ignored the true performance bikes.

Or maybe not? (I won't go into the very physical hypotheses that may explain how a frame that springs back as you push down the other side's pedal may help you overcome the "dead" spot...) -- Jan Heine, Seattle Editor/Publisher Vintage Bicycle Quarterly c/o Il Vecchio Bicycles 140 Lakeside Ave, Ste. C Seattle WA 98122