BeeSeeBee wrote:LetsRide wrote:As technologies advance in composite material and layup technique, modern carbon frames can be made both stiff and flexy at the same time but in different area. So stiff frame yet still comfortable can be possible. This thing might sound ridiculous in the past.
Truthfully, It sounds ridiculous even today. It's that "laterally stiff, vertically compliant" line we
used to roll our eyes at, but at some point adopted as truth without actually being shown any proof. I haven't been able to get a straight answer from any manufacturer about actual measured vibrational response or deflection numbers across various terrains, not just numbers quoted at the extremes (e.g. 1000N of force deflecting 10mm vs 5mm). If I hit a bump to produce that degree of force, am I going to notice 5mm of deflection as I'm bucked out of the saddle?
What's going to feel better, getting hit with an aluminum or a carbon baseball bat?
A lot of the stuff in the new Madone white paper was seriously talking about differences on the order of 0-2mm (not the comfort aspect, which again they didn't qualify at what force, but deflection while cornering and other stuff). Of course the plots exaggerate the differences, but a marketing spin is expected on them.
But this is also great, because like DeLuz, they're all seriously capable bikes these days that we're splitting hairs and wringing our hands over. Not that it isn't fun to do that, but perhaps we're putting too much emphasis on stuff that realistically won't materialize in any perceptible way.
I just don't agree in bold. Changes to new frames aren't unsubstantial or incremental, there is a huge trend in the bike industry toward frames that are super stiff laterally with more forgiveness in the vertical plane. Take Specialized. The replacement for the Tarmac SL3 which was complained about in the pro peloton as being overly vertically stiff was changed with the SL4...made friendlier to ride in the vertical plane and more laterally stiff at the same time. Virtually nobody will disagree that the SL4 is a much better bike and has turned out to be one of the best race bikes every conceived. Some say that Specialized in fact $h!t the bed with the new Roubaix SL4 which was taken in the opposite direction. Specialized changed the rear triangle of the bike and made it more like the Tarmac in back...much stiffer...resulting in supposition that the change in lateral stiffness actually degraded ride quality as the planes though opposite are in fact related...because a frame technically bends rotationally or torsionally as viewing a bike from the front. As a result, testers of the new Roubaix SL4 found the bike overly stiff to ride...not in the character of an endurance genre bike...the SL3 Roubaix being more the sweet spot of ride comfort and overall stiffness which was much improved from the Roubaix SL2 which by comparison was considered a noodle and not a performance oriented bike.
The new Cervelo SL3 comes to mind...a bike with unprecedented vertical compliance for an aero bike while not a noodle laterally. Cervelo did this by making the seat seats uber compliant and the bulk of the stiffness of the rear of the bike based upon super stiff chainstays. In fact many believe the S3 rivals the ride quality of the R3 and why many choose the S3 as there is little downside to the aero frame qualities. This is a very difficult balance to achieve with an aero bike and the S3 is actually a more livable bike within the aero genre as a result than the less aero Venge or more aero S5 which is often criticized for riding like a cattle wagon.
So what designers are trying to accomplish is not without consequence...it is in fact the cornerstone of how bikes perform and how livable they are to ride. I believe the thing that is striking is the notion of why laterally stiffness matters. We all understand why vertical deflection matters...to absorb road shock which is principally vertical in plane and attenuate rider assault and fatigue. But in spite of when this conversation comes up...and its a compelling one I often enjoy and generally without resolution, there is one immutable reality.
Bike companies want to make make their top race bikes as laterally stiff as they can. This is the common theme in the industry and the consensus of thousands of engineers that make up the industry. So why is that? Is a laterally stiffer bike faster? Does it accelerate faster? Does it tire a rider less when hammering for 50 miles in a competitive environment?...provided a given race bike has suitable vertical compliance? I believe this all maybe true and of course we all struggle to produce the math or even power meter numbers to support this. But the industry is in lockstep and I believe anybody who believes this is pure marketing is wrong. Its a substantive position. Will a better rider on a flexy bike beat a weaker rider on an uber laterally stiff bike? Like a red headed step child all day long. There are guys I can't outsprint who ride Columbus tubing steel bikes when I am on my carbon rocket ship. So the stiffness thing is not transformational as most here know who compete on the recreational level. But a stiffer bike 'may' climb and sprint better for a stronger rider in particular.
I also think some of the terminology used here is a bit sketchy. When a flexy frame it loaded or a top sprinter loads even a stiff frame that an average rider can't even flex, the frame 'stores' that energy. It isn't absorbed. There is very little heat loss if any. When a strong rider is out of the saddle, and the rider pushes his legs against the resistance of the road, the frame bends and more or less holds this bend as the rider imparts more energy than what the road pushes back aka the bike accelerates. But does the frame really hold this bend? Truth is, the frame doesn't. This is because a rider's application of power to the bike isn't linear. Its cyclic....like a pulse. The pedal stroke has a power zone and a flat zone and there are two pedals on a bike. So one would think intuitively once the frame stores energy than acceleration of the bike should be same between a stiff bike and a more flexible bike for a given rider wattage. But, I believe the benefit of frame lateral stiffness or resistance to frame torqueing may be more nuanced than that including where the real improvement in power transfer is. I believe it relates to the cyclic power of crank rotation. The power zone of the pedal stroke versus the dead zone. The reciprocating power left to right. This is sine wave of power application as it turns out. It is possible that the loss of efficiency of a flexy frame relates to the transition of dead zone to power zone of pedal rotation. Call this the power pulse. This pulse is more affected by a flexy frame which may slightly unwind every time power to the pedals is reduced. So I believe if one views power to the pedals as more of a pulse of on and off power...like a crankshaft firing close to TDC and there physically being a lag in power after the leg(s) fire thru the power zone, this probably interacts more with a flexible frame aka a stiffer frame transfers the power of the pulse more efficiently to powering the bike forward because there is less unwinding of a stiffer frame through the dead zone of pedal power on each side...so a stiff frame picks up the power zone of pedal pedal force more quickly...and this all occurs several times a minute in the 90-140 crank RPM range.
A good conversation in any event and one of almost indiscernible solution because of magnitude mostly....a good rider will beat an average rider every time on a more flexible frame.
But again, the industry marches forward with greater laterally stiff bikes and I believe its because they are tangibly faster among better riders based upon above. So I agree with the industry trend as vertical and lateral stiffness are further decoupled to have one's cake and eat it too.
Also, if you take a 1500 watt sprinter versus 500 watt Joe six pack weekend warrior, the stiffness of the frame becomes moot to Joe six pack. Joe six pack has a hard time flexing a Vitus frame often discussed as a benchmark or contrast to a stiff frame. A Vitus is almost a stiff bike to Joe six pack versus a decent amateur sprinter. So frame stiffness matters relative to who is riding the bike and whether a given frame stiffness will matter more or less. If a rider can't flex a modestly flexible frame, then there isn't any efficiency loss.
A final note. Higher lateral frame stiffness may at the end of the day matter for control of the bike during a sprint. A stiffer bike in the hands of a strong guy maybe easier to control out of the saddle when laying down big watts compared to a more flexible bike and this will translate into greater speed. So this maybe part of the calculus as well.