|FSA Carbon crank versus Ultegra||glia|
Dec 22, 2003 5:45 AM
|Two bikes, two different cranks/BBs. One a FSA carbon compact with a Dura-Ace BB the other with an Ultegra crank/Ultegra BB. Could there (or should there) be a noticable difference (~3%) in power output to the wheel?|
|A little clarification||asgelle|
Dec 22, 2003 7:19 AM
|When you say there's a 3% difference in power output to the wheel, what exactly do you mean. Are you saying that at the same speed, one bike requires 3% more power as measured at the hub or are you on an ergometer and one reads 3% higher than the other at a fixed erg. setting? In the first case, there could be a lot more variables than just the crank/BB difference. In the second, it could be ergometer calibration.
Total drivetrain losses are in the range 2-5% so it seems very unlikely that crank/BB (which acounts for only a small fraction of the drivetrain loss) could account for a 3% difference. This assumes that the BB is adjusted correctly. If a BB is too tight, power could go to infinity as with increasing preload, the BB won't turn at all.
|If I'm reading correctly.........||davet|
Dec 22, 2003 8:41 AM
|..you're asking if there is a power loss because of the type of cranks, Ultegra vs FSA carbon? If there is a power loss it is not because of that, more likely it's because one is a compact (110 bcd) and the other a 'regular' (130bcd). I would think a normal human would/could develop more power with a compact crankset, all other things being equal.|
|If I'm reading correctly.........||asgelle|
Dec 22, 2003 8:57 AM
|"I would think a normal human would/could develop more power with a compact crankset, all other things being equal."
Can you explain this. If crank length is the same, and gear ratio is the same, why would the compact crankset make any significant difference. If anything, I would expect the larger cogs of a standard crankset to be very slightly more efficient.
|You'd better be able to explain this conclusion! (nm)||Kerry Irons|
Dec 22, 2003 5:09 PM
|I can't. In hindsight, I mis-spoke (my bad)..||davet|
Dec 22, 2003 5:28 PM
|I think what I was trying to say is that a 'normal' (non-pro) can't use the bigger rings to develop his maximum power (efficiency?) as he can with smaller rings, more leg speed and cadence. So my hypothesis was that the OP was trying to equate pushing a big gear, when he thought there was a power differential, as opposed to a smaller gear, but that wasn't clearly stated by the OP.
In any event, my answer to his question if there is a power loss merely because of a difference in cranks, I would say no. More likely the difference is because he is able to use one crank more efficiently than the other. Does that sound better?
|I can't. In hindsight, I mis-spoke (my bad)..||al0|
Dec 23, 2003 1:08 PM
|There was link to comparision between cranksets (including FSA carbon and Ultegra) some time ago. Ultegra is stiffer!
So paower transfer is better.
|gear ratios rather than power||Coot72|
Dec 23, 2003 4:03 PM
|I looked at the gear inch chart and it looks like the advantage is in the ratios. A 34x25 is a tad bigger than a 39x29. This would allow you to spin up steeper hills saving the legs from fatigue. That way you may be fresher and have more power on a long, hilly ride. You lose the 53x12 gear though. with an 11x23 or 12x23 cassette, all your gears will be close together, but you would still get a decent climbing gear with the 21 or 23. The drawback might be in switching between rings. You may have to shift more cogs in the back than usual, but that is a minor thing.
My sense is that more people *should* have a 50-34 chainring setup. I am curious to try it myself, as I rarely use the 53x12. I certainly don't need a 53x12, but I could've used a 34x25 on several occasions. I'd rather have more gears in the middle.
Why doesn't shimano or campy make a 110 bcd double? having the right gears is probably more important than most popular "upgrades."
|gear ratios rather than power||glia|
Dec 24, 2003 8:23 PM
|Thanks for all the pointers in response to my original question. I would like to comment on the gear ratio. I love the 50/34 compact gearing and mostly use it with either a 12/23 cog for close gearing with good low gears or with a 11/23 cog if I need some longer gears. Overall, I find that I almost always have at least one extra gear left going up even steep hills and there may be a psychological issue here knowing you could still shift down. On my 39/53 crank even the 12/25 does not go quite as low. For very hilly long rides I still have the option of using the 12/25 with the 34/50 for really low gears that compare to the low end of a triple. So I do agree that this may be the ticket for many more riders.|| |