Cranksets....need your advice

Triathlon Forum
21

Bad application of a good idea does not invalidate the idea. The Litespeed Internal HS design has/had a couple of failings:

  • relied on taper of Bearing set to self-center the races

  • expensive to manufacture in the chosen material (TI)

  • resulted in heavier bare frame weight, even if complete bike was lighter

  • People who spend that much money on a frame feel a compulsive need to spend $100 plus on a headset, rather than the 15 bucks a comparable bearing set costs.

The problem with oversize BBs is that the BB cup standard is too small. Period. External cups are an attempt to deal with this, and are a temporary fix until the standard inevitably changes. Low bearing life is 100% a result of this.

I really get a kick out of these arguments regarding bearing interface design. I have asked the question before, and I will ask it again: if “internal” headset and BB designs are so bad, why is it that bicycles are the only common application that has not adopted this style of interface as (nearly 100%) the standard? If someone were to suggest, in a non-bicycle application, that a manufacturer press-fit an entirely seperate assembly into a tube, merely to support a press-fit sealed bearing, they would likely get laughed out of the room.

.

22

So are you saying that putting, say, a Dura Ace crank on a trek 1000 will stiffen the frame up? That’s interesting. Where is the documentation on that?

23

No, I am not saying that.

.

24

Ok, so what exactly is the real world performance benefit of outboard bearings if you still have frame flex in the BB?

25

  1. The primary purpose of external bearings in BBs is to allow the use of a larger OD BB spindles, which provide increased stiffness for the BB unit. Wider bearing stance does have a slight effect on stiffness, but this is a secondary design artifact

  2. This stiffness is desireable, as the crank/bb unit is (obviously) a primary recipient/converter of muscular force. Stiffness in this unit results in increased efficiency in the transmission of muscular energy to the bicycle drivetrain.

  3. The efficiency of this system can and should be optimized.

  4. This optimization can be considered as a discrete operation, seperate from the considerations of frame design, other than as they effect the standardization of the design parameters.

Further:

“frame flex” needs to be usefully defined to be considered, and does not occur in nearly as simple a manner as would be readily apparent, especially as regards drivetrain function.

“frame flex in the BB” is essentially non-existant, if by BB we are referring to the BB shell. If by BB we are referring to an undefined bottom-ish area of the bike, than it does in fact occur, may well be the source of inefficiencies, and it’s consideration is of absolutely no value in a discussion of the relative efficiencies of different crank/bb configurations.

EG: “Who cares how stiff my crankset is - I am riding in a 6 foot pool of peanut butter.”

  "Who cares how stiff my crankset is - I am riding a late 80's Vitus" 

  "Who cares how stiff my crankset is - It's mounted on a bike I never ride"

All good questions; all also completely irrelevent to the discussion at hand.

.

.

26

I also thought the use of the outer bearing style was to eliminate weight and parts at the expense of life cycle…i still can’t figure out why the BB has to be so complicated to begin with…

I do have one question in regards to the integrated headset design…i can’t figure out for the life of me why there is no sleeve in between the upper and lower bearings to allow support and compresion limits…this is the only design that i have come accross like it, every bearing on a car is supported and limited and last a long time…just how long will those headsets last???

27

I still dont know what was fixed…larger spindly…were the old ones breaking (I never seen a spindle break). I never seen one flex, never heard anyone claim theirs did either for that matter. Never heard of people complaining that their (quality) BB’s were wearing out any faster than 10-15 years…oh…and dont forget that the Record Carbon Crank with the Record BB is LIGHTER than the new DuraAce…where again is the benifit? I am missing something I am sure.

28

““frame flex in the BB” is essentially non-existant, if by BB we are referring to the BB shell. If by BB we are referring to an undefined bottom-ish area of the bike, than it does in fact occur, may well be the source of inefficiencies, and it’s consideration is of absolutely no value in a discussion of the relative efficiencies of different crank/bb configurations.”

Wow, you completely missed the point, didn’t you. Maybe we are just having different discussions. To enlighten you, the discussion at hand is not about the relative efficiencies of different crank/bb configurations in a lab environment or on paper. Rather, we are discussing whether or not a “stiffer” BB/Crank configuration has any benefit if there is still lateral movement in the “undefined bottomish-area of the bike” (commonly referred to in cycling circles as the BB area or, when referring to frames, simply the “BB”)when pedaling under load.

Feel free to chime in with something relevant.

29

So I guess we have decided that there is no actual improvement in performance, and probably a higher rate of failure with the external bearing systems…neat…

I have ridden Shimano DA10…and ride Record on my bikes…blind fold me and I cant tell you one crank from the other when I am riding…maybe I am dumb.

30

Thanks for “enlightening me…”

Are you attempting to ask/say:

-the issue of crank/bb stiffness is irrelevant because the benefits of increased stiffness in this area are lost in frame flex inefficiencies/noise?

or,

“who cares about a stiffer crank, you don’t lose energy there, because the frame is flexing already!”

If this is what you are trying to say,

  • frame flex does not really work that way in regards to the drivetrain.

My distinction between BB and “commonly referred to as BB” is actually meaningful in a real discussion of the issues you attempt to raise. The only source of flex in the actual BB area is the spindle/crank. This interface is subject to quantifiably different forces than the area you seem to be referring to in your over-generalization. To simplify: flexion of the spider, crank arms in 3 axes relative to the BB centerline, and chainring flexion are all factors in this phase of energy transfer, and are not, or manifest differently in a discussion of frame flex.

  • You are losing energy there, so yeah, it does matter.

Well, maybe it doesn’t matter for you, but it does for many riders. ST BBs are flexy, measureably so, and not in a way that is completely lost in the noise of frame flex, which doesn’t affect power transmission in a bicycle in the same way that BB flex does. Why ride something you know to be less efficient, even if microscopically so?

I stopped using Campy cranksets when I actually saw a set of stiffness tests for the Record crank/BB (and no, I don’t have them sitting around anymore, sorry, wish I did.) They are markedly less stiff than any of the competition, almost all the difference comes from the BB, and the results were more than enough to convince me.

PS - I still have a set of Record AL cranks, 172.5, sitting in the closet; sold the other two sets. I will make somebody a good deal on them… but will also tell them up-front that a set of the cheap FSA AL cranks, with an ISIS bb will outperform them on any given bike (as long as the crappy bearing set holds out, anyways…)

.

.

31

Are there any studies that show the extra stiffness in the BB will have a SIGNIFICANT effect on performance? Exactly how much energy is lost?

There are a lot of things on the bike that could be microscopically improved that will have virtually no effect on real world performance. Just because you get an almost immeasureable benefit does not necessarily make something superior if it costs more, requires higher maintenance or is imcompatible with other parts.

32

You are a real beauty, and I do mean that in a nice way. You argue in a logical engineering thoughtfulness on how internal bearings work better and some cranks are stiffer and it is now the industrial norm. Then state how you have switched based on an article that plainly shows that one crank bearing/BB system is what 5% stiffer? While you ignore the fact that the bicycle is an engineering dinosaur.
Look at the way we shift gears, we use a stick to drag or push a moving chain to another gear and then ride with a chain that is not even on straight. Yea that is an engineering marvel at its finest. And you worry about crank stiffness?
With that kind of engineering I will take my old Campy cranks with Phil Wood BB set ups for the next thirty years or so on my Matt Chester, Merlin, Moots, and Dean Ti bikes which I plan to still be riding on at that time when I turn 84. And with Phil some of the same BB will probably be with me. Call me “old skool” but I don’t think even a 100% increase in crank stiffness would knock 3 seconds off my 40k TT split. But following Shimanos changes in bearing and BB standards sure will knock a few hundred bucks out of my wallet.
When I race TT my chainline is perfect (I race fixed) Every time you race, think about all the watts you lose in mechinical drag on your rig with that chain on crooked. And how those stiffer cranks are actually increasing drag as they aren’t flexing with the load as much as that guy with the old sskool BB .Cheers G

33

I think that what I need to do is get steel studs mounted to the bones in my feet…these studs will attach directly to my cleats that will snap directly to the studs, and thus directly to the bones in my feet (much like artificial teeth). This will in turn give me the best possible connection to my pedals and the bicycle with out the robbing of energy caused by the sole of my foot compressing, and my shoes flexing.

My gawd am I going to be fast…time to take out all the weak links folks…

34

“you ignore the fact that the bicycle is an engineering dinosaur”

Whatever.

The modern geared bicycle is one of the most efficient means of transportation ever created, THE most efficent mechanism for human powered locomotion yet devised, and, in fact, not at all what you are claiming.

And, btw, the increase in efficiency of a fixed gear bicycle over a geared one is statistically insignificant (you might want to look up the research.)

“increasing drag as they aren’t flexing with the load as much as that guy with the old sskool BB”

Huh? Nonsense. Pure flatulence.

35

I have seen more than one time (Myth Busters too I think) that the chain and cog are one of the best ways to transform energy.

36

Yup. No question about it. Nobody has been able to top chain drive for low power applications, especially when weight is a factor - and many, many people have tried.

.

37

I’m still waiting to see some hard evidence that increased BB stiffness will lead to better performance. In fact many bicycle components, including the frame are not designed strictly for stiffness. Isn’t it possible that a less stiff BB might actually reduce fatigue due to road shock?

38

Show me a modern marvel besides the bike that they intentionally design the chain to drive in another direction besides straight. That is why we wear out chains so quickly. My dirt bike chain moves at what 10 times the speed of my bike chain and lasts mult. years. Ask any design engineer, they will laugh at the inefficiencies of the deraileur bicycle drive line, but have yet to come up to a better alternative. I agree that the bike is a timeless invention, but to worry enough about BB flex to change systems is a waste of money…
I am no scientist, but I know that you lose more watts of power to chainline friction than BB flex. Maybe you can show me a study that mentions different, but I would think there isn’t one out there.

39

“Isn’t it possible that a less stiff BB might actually reduce fatigue due to road shock?”

It’s been tried, and it’s a bad idea.

40

G-man,

  1. I am not arguing that anyone should change crank systems.

  2. Design engineers do not laugh at the inefficiencies of bicycle chain drive lines. (I stand next to one 40 hours a week.) I repeat; the modern geared bicycle is the single most efficient means of transferring human energy into locomotion ever devised. The main reason for this is the incredible efficiency of chain drive systems, and one of the great things about chain drive is it’s ability to remain incredibly efficient when linking non-aligned cogs (as compared to, eg, a belt drive.)

  3. The main reason for the longevity of your dirt bike chain is mass, and yes, the fact that it is held in alignment, and the fact that it is not derailed. Chain wear can not, in and of itself, be used as a basis from which to draw any meaningful conclusions regarding drivetrain efficiency.

  4. you aren’t a scientist.