rpenmanparker 

We don't often agree, but chalk this one up as a good example of when we do. You are 100% right on.

rpenmanparker 

And you know this how?

dalava

Who needs science when you can feel it....

But, better is better, so there is that.

thump55

It takes power to flex the BB.
If the BB does not flex, that power is used productively instead.

Marin

Do you really beleive that? Ever feel your bottom bracket area? Does it get warm?

macca33

Do you have any photographic evidence depicting you licking your BB???? Is there a BB-lickers Anonymous group in your area?? Hahaha

79pmooney

If your frame is metal, very little heat is lost on frame flex. That energy is returned nearly in full when the metal springs back. (This property is known to the engineering world as elasticity, a trait of many metals. There are exceptions. Lead, gold. Now carbon fiver does not have that property. When you flex it, some energy is lost on the return. I suspect the resin content of the laminate and how carefully stretched the fibers are has a lot to do with it, meaning a very high quality vacuum bagged frame probably has far less loss than a cheap copy. Nevertheless, a stiff CF bike will have less loss than an equal quality less stiff bike.

And back to metal bikes: if lack of stiffness was such a huge disadvantage, would someone like to explain to me how Sean Kelly won so many races in sprints riding one of the most flexible bikes every raced, the skinny aluminum tubed Vitus?

Ben

VNA

Flex equals loss of energy--more energy going to the wheels the better with the least amount of flex!
It also makes a bike more responsive particularly in sprints or going up hills at each revolution!
One of the reasons road bikes do not have suspension--"real" road bikes like the tour de France!
And NO-- bikes are not created equal, that is why there are so many models/manufacturers

Psimet2001 

I have melted a few. Back in the steel days. Now they just explode...err...asplode...

anotherbrian

My VAM went from 900 to 990 for the same Powertap-measured effort (~280W) on 13x repeats of a 0.5mi 9% hill between my steel Ritchey Break-Away and carbon Tarmac Pro.

Tarmac weighs 4lbs less than the Ritchey. I weighed the same (~200lbs), +/- the usual daily lbs or two.

Point

I take it you're not an engineer

joejack951

Lead and gold are very slightly elastic. Lack of published figures for an actual yield stress seems to be due to the difficulty of accurately measuring it. Doesn't mean they can't deform elastically, just that the deformation quickly goes to plastic deformation.

Carbon fibers most certainly have an elastic region even in pure tension. What they lack is a plastic deformation region, much like glass. Their elongation at break is tiny compared to all but the most brittle metals as well. But focusing on the tensile properties of the fiber itself is akin to focusing on just the paint of a high end frame. it doesn't even come close to telling the full story of the material. Carbon fibers can be layed up to function like a steel spring (check out the Look Keo Blade pedals) or be about as unyielding and brittle as carbide tool steel.

Wingsprint

False.

Wingsprint

Nothing to add here. Great post!

thump55

Please explain your theory. And be sure and use small words so us mere mortals can understand.

Campag4life

I don't agree...not pure marketing. Lets say the debate of stiff versus non stiff BB in terms of energy transfer is moot, difficult to prove or doesn't manifest much difference. This can't even be painted with a broad brush because rider's vary so much in weight and power. I am a mechanical engineer btw. I believe there is energy loss due to the wind up of the BB, downtube and rear chain stays as energy when stored due to displacement when returned almost a hundred times per minute due to power zone of the pedal stroke versus dead zone is not perfectly conserved. Better to not store it but directly transfer it and not just because of potential loss but because of 'control'. Distortion of the BB center due to aggressive pedaling moves the pedals outside their typical arc as compared to pedaling at lower force. A whippy frame has a harmonic based upon pedal force input. This is a pulse as there is a power zone and dead zone...one on each side of the bike. This can manifest a control issue to having the best pedal stroke. A further issue when it comes to frame stiffness that seems to elude many is a stiff frame typically handles much better...or rather an ideal stiffness to rider weight frame. This is the centerpiece of what Specialized tried to accomplish with the new Tarmac based upon all their strain gage testing.
The other thing I believe you are wrong about is...the bike industry which has moved well into the realm of computer modeling employs thousands of engineers. It isn't just one or two companies that believe a stiffer frame is faster but ALL of them. There are no whippy frame backlash designs to stiff race frames among the race frameset collective in the industry. Lateral stiffness for energy transfer AND vertical compliance is the mantra and for good reason. A stiff frame when sprinting or descending or with high speed handling is a controllable frame and therefore a faster frame. I have owned countless bouncy bikes like your iconic Vitus often referred to as a gold standard for whippy frames...and I am faster in all categories on a stiffer carbon frame. To me, there is no comparison.

There are many flaws in your BB argument as well including growing the size of the BB increases down tube and chain stay cross section which lead to greater lateral stiffness and more efficient energy transfer. I have worked on countless bikes over the past 5 decades and to me square taper sucks compared to external bearing BSA. Both Campy and Shimano external bearing threaded BB is not only uber stiff but have greater bearing life. I got about 18K miles on my original Campy UltraTorque bearings for example...and no cartridge to replace as with square taper either. To me, external bearing BSA BB's were a huge step forward. I stop there with BB30 and PF30 however. I believe with both the industry screwed up...PF30 in particular is an abomination. BB30 can be managed but I vastly prefer external bearing BSA BB's.

My counterpoint.

BillyD

Family forum.

redfooj

i like how the industry trend was for stiffer and stiffer seatposts, even to integrated types, and now theyre saying softer posts are better, with inserts, thinner diameters, split-design, etc

i wonder if they'll market reversal in other areas of the bike as well

Campag4life

No...just further decoupling between vertical compliancy ergo seatpost a la Domane/new Madone and uber lateral stiffness which is most efficient for propelling the bike. Ride comfort matters...so does efficient energy transfer.

joejack951

I don't doubt that stiffer seatposts were touted as beneficial at some point if for no other reason than aluminum frames had larger I.D.'s than steel tubes which forced larger diameter (and stiffer) seatposts on those frames. Marketing departments can find the upside of anything.

StanSeven

Really? Cannot afford engineering talent? Specialized has a brand new facility filled with engineers and their own wind tunnel. Cervelo has more engineers than any other employee group.

Did you try and get a job in the industry and were turned down?

Psimet2001 

External BB's were a huge leap. Way stiffer and for me at least it was greatly appreciated. BB30 and PF30 are horrible.

There are tons of engineers in this industry. Some of them better than others but they are here. We toe the line with way too many of them from SRAM just about every week. They are smart, skilled, and can also usually kick just about everyone's ass on a bike as well.

Seattle Forrest

Doping?

kc0bbq

A rider with Festina and Panasonic? Unpossible.

Dave Mayer

I’m an engineer. Never bothered to inquire, but I doubt the bike industry could pay enough.

Any real bike industry engineers here? Are complete bike systems computer-modeled with dynamic finite element analysis? Including the wheels? And the rider? I thought not. So without this deep analysis, how does the industry know that a flexible frame results in power losses? For the first pedal stroke, the stiff bike may accelerate faster, but eventually the frame flex gets returned. A metal bike frame is perfect spring. Where would the power losses go? Heat? Anyone here notice their frames heating up after a stiff climb?

Anyway, the external BB was one of the most pathetic kludges ever developed within the bike industry. To recap:

1. This came about because the bike industry needed a larger diameter bottom bracket spindle. For no real reason except for planned obsolescence and locking customers into proprietary standards.
2. The existing standard BB hole in the frame was too small for the larger spindle.
3. So instead of making a bigger hole, put the bearings on the outside of the frame where they are exposed to the elements. Seriously?
4. Recent frame developments provide bigger holes so that the BB bearings can be put into the frame where they belong.
5. The next development in the industry will an arms-race of ever expanding bottom bracket holes. If a 24mm spindle is good, then a 30mm spindle is better. Why not a 100 or 1,000mm diameter spindle? Which will spawn another proliferation of new incompatible BB ‘standards’. Or have I missed something, and this is already happened…. Could not be bothered to check.