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From WW
Shimano built up some outboard track crank setups for the Australian and British teams to test. They didn't like them. The biggest complaint was that the larger bearing circle with the outboard cups couldn't be made as stiff under high wattage as one contained within the bottom bracket shell. They also didn't like the larger bearing diameters -- there always has to be some slight slack between bearings so they don't rub against each other, and again under high wattage outputs the axle would tend to force a gap in the bearings (even with a clip in place) and have to click over each bearing. This isn't a problem at the maximum outputs experienced in road racing, but a track sprinter is something else
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interesting stuff, thanks.
Here's the ww link if anyone is interested:
http://weightweenies.starbike.com/forum/viewtopic.php?f=3&t=46539&p=439811&hilit=Shimano+built+up+some+outboard#p439811 -
From WW
Hmmm... Cartridge bearings of the size used for external BBs are designed for bigger loads than even track sprinters put through them, and the cage would have to disappear completely before the balls could be far enough apart to significantly affect radial clearance. The post you quote goes on to spout some even more tenuous bullshit about rider feedback
if it doesn't flex at all the rider actually can't ride at maximum output as well. This is why some riders prefer to go for less-stiff crankarms (such as Sugino Grand Mighty or SRM track powermeters). More flex doesn't mean lost energy -- it means a rider at the limit can manage the limits of his power input by allowing the cranks to work with him a bit.
The proper answer:
Power lost in flexing your BB spindle and cranks is vanishingly small compared with everything else. Old fashioned cranks are good enough for top riders. External BB cranks are perceptibly stiffer in terms of torque wind up of the axle, crank arm stiffness is another matter and largely independent of BB design. When it comes to solid aluminium cranks, they are all about the same shape, so the heavier ones tend to be stiffer. The limiting issue with cranks is, once again, torsional stiffness, so the only way to improve them is by moving material from the centreline where is does fuck all good to the periphery of the cross section, which is why Shimano Hollowtech cranks always test so well.The Omniums are cheaper than Campag by the price of the Campag BB, they are stiffer (I've ridden both, and you can feel the difference), albeit that the extra stiffness will make about 0.0001% of fuck all difference to your performance, but also quite a bit heavier, again a matter of almost no consequence on a track bike but it might amount to 0.2% of your total bike+rider weight, which could hold you back by 25cm on the first (250m) lap of a standing start event.
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Dura ace sprockets, Sugino cranks, Sugino chainrings if you can afford or Blackspire if not. Sram or Izumi chain.
Phil sprockets, Goldtec chainrings, Wippermann 1R8 chain
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Campag has the lowest Q factor.
Anyway, I use Stronglight on the track, so I don't really feel part of this whole discussion.
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££££££££££££
no?
The sprockets are expensive, but the rings and chain aren't.
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The Omniums are cheaper than Campag by the price of the Campag BB, they are stiffer (I've ridden both, and you can feel the difference), albeit that the extra stiffness will make about 0.0001% of fuck all difference to your performance, but also quite a bit heavier, again a matter of almost no consequence on a track bike but it might amount to 0.2% of your total bike+rider weight, which could hold you back by 25cm on the first (250m) lap of a standing start event.
That's some authentic frontier gibberish right there.
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That's some authentic frontier gibberish right there.
I actually did calculations, assuming acceleration from a standing start to 33mph in 15s, the extra 200g robs you of 1.5W, out of 750W required for accelerating you and the rest of your bike and about 600W of aerodynamic drag at the maximum speed. Working back to distance covered in the time with the acceleration reduced to account for the extra mass puts you about 25cm behind after one lap.
Other things which are in the >1W gain range:
Changing from a very good tyre to the best one
Changing from a very good aero helmet to the best one
Changing from a very good pursuit bar to the best one
Moving your elbow rests by 5mm from where you are to where you should be
etc. etc.If you're in the accumulation of small gains game, the choice between Campag and SRAM cranks needs to take account of bearing drag and aerodynamics as well as weight and stiffness, because they are all going to be in the same order of magnitude. You need to measure on a full system, since bendy BB axles cause chain misalignment, so you need to measure transmission losses too. It's not even enough to measure the mechanical losses, since crank twisting causes the pedals to be canted under load, which likely has a physiological impact on the rider's ability to exert maximum power. If you don't have the resources to measure all these factors under full load full speed conditions to a resolution of 0.1W, you might as well go with aesthetics since they are both good.
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(I haven't read from page 1.
I am wanting to build/buy a very nice track bike for all-round track racing.
This is the track sub-forum, the assumption is that going as fast as possible around an actual track is the aim.
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If you don't have the resources to measure all these factors under full load full speed conditions to a resolution of 0.1W, you might as well go with aesthetics since they are both good.
That's good to know both are highly considered for track riding and either way they'd be up to the job. On further reading I noticed a few people having chainline problems with the Omniums as the chainring bolts can strike wider chainstays (http://www.lfgss.com/thread29215.html).
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What frame are you putting the cranks on? Post a pic and the answer will appear.
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I actually did calculations, assuming acceleration from a standing start to 33mph in 15s, the extra 200g robs you of 1.5W, out of 750W required for accelerating you and the rest of your bike and about 600W of aerodynamic drag at the maximum speed. Working back to distance covered in the time with the acceleration reduced to account for the extra mass puts you about 25cm behind after one lap.
Where did you get 750W from??
And what would the 25cm equal in time (my maths isn't working today) it seems like a pretty big gain for a loss of 200g on a bike, simply going from the steel nittos to a carbon bar would probably do that, yet it's never reflected in the times.
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I guess they'd be stiffer being 7050
This, by the way, shows that SRAM marketing is winning over education. There is no meaningful difference in stiffness between different kinds of aluminium alloy, and you don't know which alloy Campag are using anyway. I've just looked up data sheets for typical Dural and Zicral class alloys, and the Dural was actually rated slightly stiffer (Young's modulus) at 73.1GPa for 2014 vs. 71.7GPa for 7075
Alcoa don't even think stiffness is worth mentioning in their marketing of 7050 http://www.alcoa.com/global/en/products/product.asp?prod_id=606, the main selling points being better resistance to stress corrosion cracking and better suitability for thick sections compared with typical 7075, neither of which seems especially relevant to a fairly thin track crank.
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Where did you get 750W from??
And what would the 25cm equal in time (my maths isn't working today) it seems like a pretty big gain for a loss of 200g on a bike, simply going from the steel nittos to a carbon bar would probably do that, yet it's never reflected in the times.
750W is the average power needed to accelerate 100kg of bike+rider to 15m/s (33.5mph) in 15s.
Kinetic energy = 0.5 x 100 x 15^2 = 22500J
Power = 22500/15 = 750W25cm as you cross the line at 15m/s is 0.25/15 = 0.016s. Bear in mind that that only applies to acceleration, any steady speed effort is almost completely unaffected by the mass of your bike, apart from a tiny change in rolling resistance. Because most of the acceleration happens early in the lap (when you have a bigger surplus of output power over combined drag + rolling resistance), you spend most of the time doing a speed where more than half your power is consumed by drag, so that is always where your resources should be spent, ahead of trying to lighten the bike.
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