greg
new member
Reged: 04/19/04
Posts: 2
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What is the work on the street about cranks. I am 220 lbs and curious about FSA or equivalent carbon cranks. Is this something to consider, or should I stay with DA or Ultegra stuff. What would be the advantages of each over the other?
Thanks.
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flythebike
captain
Reged: 08/26/04
Posts: 272
Loc: N. Virginia, USA
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Carbon cranks are often heavier than their aluminum counterparts. But proponents may argue that they 'feel' better: stiffer; that they offer more torque, they are more comfortable, and they (especially Campy) look better. They won't make you a lot faster, but they might make you a little faster, and make your bike look cool. Spend your money on the frame and fork, then the wheels. Cranks are important but not at the top of the list. I have Campy Carbon Chorus on my Dragonfly and I like them a lot, but the difference between them and aluminum Record is subtle. I have FSA compact carbon cranks on my cross bike. They are not all that light. Again, check www.weightweenies.starbike.com and you'll see the weight differences are generally very small. The notable exception is the $800 Zipp carbon crankset which weighs only 397 grams with chainrings, arms, and chainring retaining bolts. I just bought a T/A track crank for my fixed Luna and by contrast it weighed 475 grams for the arms alone, 615 grams with chainring, chainring mounting bolts, and crank mounting bolts.
Edited by flythebike (03/02/05 05:59 PM)
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BikerDoug
friend
Reged: 12/29/03
Posts: 88
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I weight 260 and put FSA Carbon Pro Compact on my Tetra. I probably would have gone with the Dura Ace 7800 cranks because of the supposed increase in stiffness, but I wanted to try a compact (which I found I thoroughly enjoy).
I just purchased the new carbon FSA SLK Compact MegaExo that has external bearings similar to the Dura Ace set. Hopefully they will be as stiff. I will be installing them before my ride this weekend. I'll report on my impressions if anyone is interested.
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flythebike
captain
Reged: 08/26/04
Posts: 272
Loc: N. Virginia, USA
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Bikerdoug raises a key question: how stiff is stiff enough? You may not really need the stiffest cranks out there. FSA says that outboard bearings provide an incremental increase in performance. They are not going to give you wings, but they should offer a marginal benefit in stiffness and durability. Probably not worth going out and replacing your perfectly good stuff. But if your gear is worn out, or you're putting something new together, it is certainly worth considering going with the outboard bearings. Bikerdoug, we'll look forward to your report.
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bfd
journeyman
Reged: 12/22/03
Posts: 77
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OK, here's a sort of related question. Can any recommend a good square taper compact 110bcd crank? I have a phil wood mag-ti bb that has shimano square taper and was wondering what's available. Most companies like FSA, Ritchey, etc., make a compact crank for either an octalink or isis bb. Thanks.
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flythebike
captain
Reged: 08/26/04
Posts: 272
Loc: N. Virginia, USA
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Campy now makes a carbon compact crank. If you have the money that would be your best shot. Cheaper options might include Stronglight or Bicycle Specialities T/A, although I don't know if they make a compact crank or not. But I just bought a square taper track crank made by Specialities T/A. They're French with a Canadian distributer, and www.peterwhitecycles.com carries their stuff. It is nice. Their website is www.bicyclespecialities.com. I can't remember Stronglight's web address.
I have that same BB so I refused to go with one of the newer bb styles. I bought a Chorus Carbon Crank. I was running compact last year (FSA) but the Dragonfly (over an Airborne) seemed to give me another gear so I went with the standard crank instead. There is nothing wrong with square tapered bbs. They work just fine. Somebody out there may be strong enough to flex 'em, but it ain't me babe. And I think that the bearings don't burn out too fast.
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Insightdriver
captain
Reged: 03/07/04
Posts: 472
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regarding crank shapes. Granted square works fine. The more modern shapes distribute forces over a larger area of surface due to the extra faces to bear against. This increases durabilty basically, not stiffness. Outboard bearings, being physicall closer to the forces applied on the cranks can allow a stiffer bottom bracket assembly to be lighter than an older design for the same durability. Much of design imrovements, in my opion are not marketing, but improvements from a manufacturing or engineering point of view.
For carbon fiber cranks the best ones are as stiff or stiffer than any aluminum, ti or steel crank arm if the designer made them that way. Obviously some designers aim for lightest weight and sacrifice stiffness. Pound for pound, though, nothing beats carbon fiber for stiffness to weight ratio. For years the parts in airplanes are increasingly being replaced by carbon fiber because of inherent advantages. Nothing flies that does not exceed the specfications of the metal part that it replaced. Carbon fiber in bicycles is not exotic, rather it is a new lower-end market for carbon fiber composite engineered products.
The Space Shuttle has large carbon fiber panels on it. All the newest big commercial aircraft have increasingly greater percentages of their weight consisting of carbon fiber composites. Carbon fiber composites are the major structural parts in all the highest performace fighter jet aircraft in production today.
If engineered to be the same in every respect to an aluminum part, the carbon composite part would be lighter, hands-down.
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flythebike
captain
Reged: 08/26/04
Posts: 272
Loc: N. Virginia, USA
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No doubt. The outboard bearing designs are superior. But the FSA spokesperson even said that it is an incremental improvement. When I burn out my old stuff, clearly that is a good direction to go. When Phil dies, I hope Campy can hook me up.
Clearly you can overbuild something like I think the FSA team pro cranks are overbuilt. Definitely if you do it right carbon is lighter and stronger. The question is, who is doing it right?
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bfd
journeyman
Reged: 12/22/03
Posts: 77
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<regarding crank shapes. Granted square works fine. The more modern shapes distribute forces over a larger area of surface due to the extra faces to bear against. This increases durabilty basically, not stiffness. Outboard bearings, being physicall closer to the forces applied on the cranks can allow a stiffer bottom bracket assembly to be lighter than an older design for the same durability. Much of design imrovements, in my opion are not marketing, but improvements from a manufacturing or engineering point of view.>
I will agree that outboard bearings seem to be the way to go, especially if lighter weight is the goal. However, Campy still uses square taper bb and it doesn't seem to affect those who use it. After all, if pro racers are any indication, at least 1/2 the pro peloton uses Campy and thus, still use the square taper bb. Yeah, Lance wins all the TdF, but there's alot of other racers who win with Campy setup.
As for carbon cranks, my main beef is not that about stiffness or lightweight, but about durability. Carbon is not as good with "impacts" as aluminum. When that chains fall off the chainring and onto the crank, and we all had that happened, how is that carbon going to take it? On the aluminum crank, at most it scratches the crank. What about carbon?
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flythebike
captain
Reged: 08/26/04
Posts: 272
Loc: N. Virginia, USA
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I have thrown my chain a lot with the FSA cranks, and they stood up to it. Hides scratches pretty well too.
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Insightdriver
captain
Reged: 03/07/04
Posts: 472
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We must realize that in some of the toughest environments, carbon composite structures are chosen over metal. There are carbon composites used in landing gear of modern fighter jets. Compression molded parts like cranks are very tough structures. Even if a chain gouges a crank there is a great margin of safety built in. I am considering the beating my aluminum cranks have taken and realize the carbon cranks can take it and last longer than aluminum. Carbon composite structures have flex characteristics that rival steel in that they will not fail when flexed over time, unlike aluminum that has a definate failure point when flexed over time.
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