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Clydesdales/Athenas (200+ lb / 91+ kg) Looking to lose that spare tire? Ideal weight 200+? Frustrated being a large cyclist in a sport geared for the ultra-light? Learn about the bikes and parts that can take the abuse of a heavier cyclist, how to keep your body going while losing the weight, and get support from others who've been successful.

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Old 08-14-09, 02:49 PM   #1
flesh_pile
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Best square taper BB for a 190lb racer on 200mm crankarms?

So I just picked up a set of Zinn 200mm square taper crankarms (I'm 6'6" with a 37.5" inseam) and am semi-concerned about the bottom bracket breaking with the extra 15% torque they'll generate over 'standard' cranks and the fact that they are the older, less stiff square taper setup (I'm regressing from an Octalink and ISIS fleet of bikes which in theory is much stiffer/stronger). What is the 'best' or 'strongest' square taper bottom bracket in this forum's opinion? I saw some pictures of a broken ST BB where it failed along a stress riser that was an inherent design flaw. I've also seen some pictures of very nasty calf wounds down to the muscle/bone due to chainring/BB/crank failures and don't want to suffer the same fate (or fall into traffic and get run over) if something in the crank system fails spectacularly. I'm not quite Clydesdale weight but am pretty close and am an elite level amateur racer that can probably put out roughly similar torque values to some of the bigger guys here. I know track racers used to (continue to?) use square taper BBs, but they're much shorter (102mm). I'm also probably going to have to use a triple crankset length BB (110+mm) to clear my chainstay and I'm not sure if they make 'race quality' BBs in that length. Plus I'm guessing as the BB gets longer, it gets weaker. Or will the chain break before a BB ever shears? I've never had either happen to me yet (fingers crossed) and plan to keep it that way.
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Old 08-14-09, 03:25 PM   #2
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Fleshpile,

As long as your bb spindle is a "quality steel" one, I wouldn't worry about it. In my younger years when attempting to become a racer I broke most of the various drivetrain components one or more times(chains, freewheels, pedal spindles,etc.) The only bb spindle I broke was a ti super record. Swapped that out for a steel sugino and never had another issue. Broke both ti and hollow steel pedal spinles and moved to only solid steel, only one broken since in 25 years. Chains, freewheels/hubs continue to be more of a concern. I continue to insist on riding 9 speed and with only steel freehubs. This may or may not be warranted, but, it's what I do. I'm sure there are plenty of big guys cranking huge power numbers through 10 or even 11 speed drive trains. I'm just more interested in worry free fitness and don't really see the need to accept reduced durability for little to no gains.

By the way. For what it's worth, I'm considering making the same move as you to longer cranks, 195's or 200's, I currently weigh in excess of 275lbs and am not concerned about my bb spindle. I would, however, like to hear how the longer cranks work out for you.
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Old 08-14-09, 04:54 PM   #3
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Okay. Thanks for the reply. I had already sort of scrapped any Ti plans for my BB as it's weaker than steel and I've heard some bad things about Ti BB spindles being prone to breaking. It sounds like I'm going to have to go with a 119mm spindle to get around the chainstay of my standard road bike. I'd like to have a go at making my own custom frame sometime over the winter so I might see if I can finagle the design so it's still a 130 spacing but can clear a 200mm crank without a huge, triple length BB. As far as chains go, I have never snapped one on the road (9 and 10 speed), off-road (9 speed), or on the track (3/32" setup with a 7/8 speed chain, mainly mass start racing)

I'll try to post up my initial thoughts on the cranks and then a more in depth, accurate review after a few weeks/months after I get adjusted to them. I'm probably going to move up a few sizes in chainrings to make up for the drop in cadence that will most likely occur when I make the switch. I'm thinking a pair of Dura Ace triathlon chainrings in a 56/42 configuration. Hopefully I'll still be competitive in a sprint next year even with a lower cadence.

FYI, I currently run DA 180mm cranks after riding for a few years on a mix of 170, 172.5 and 175 millimeter cranks (whatever was cheapest and available on Craigslist/Ebay). After doing some research, I realized with my height I should be going longer but the only mass market ones available were the DA 180s. I definitely noticed a difference switching up to them - I'm not sure if I got faster (probably not), but it felt nicer. I didn't feel like I had to adapt to them over the course of a few weeks - they felt fine right away but I only bumped up 5mm or 2.8%. The 20mm jump up might take a little getting used to as it's 11.1% but I've got 7 or so months before I plan on racing on the road again...
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Old 08-14-09, 05:18 PM   #4
txvintage
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Yikes, that's a long BB spindle. I think you are on the right track thinking triple. You might look on e-Bay for one of the Token BB's or do a web search, I think Jensen had them for $30 or so but I don't know if they are that long.

Honestly, the best bet may be asking your best local wrench at an LBS that supports local racers.

EDIT: You might shoot BF member Mazama a PM. He's a 7 footer and rides custom. He might have some experience in the Uber BB search.

Last edited by txvintage; 08-14-09 at 05:25 PM.
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Old 08-14-09, 07:25 PM   #5
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Originally Posted by flesh_pile View Post
Or will the chain break before a BB ever shears?
Yes. The only square taper BB I have experience with is the Shimano UN54, but it appears to have an extremely solid thru-axle. My guess is that you'd destroy the chain, rip the teeth off a sprocket, or shatter a crank arm before you'd damage a UN54. I've heard about lots of bike parts failing catastrophically, but never a bottom bracket...
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