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rbent Forum
https://rbentonline.org/YaBB.pl General Category >> Technical >> Gettin' cranky... https://rbentonline.org/YaBB.pl?num=1204904019 Message started by FlyingLaZBoy on Mar 7th, 2008, 9:33am |
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Title: Gettin' cranky... Post by FlyingLaZBoy on Mar 7th, 2008, 9:33am There are various posts in various places about the effects of crank length... 170-175mm long cranks appear to be "standard", but some swear by 155's, and I know Terry P likes 180-185s!!! Has anyone installed 155s as a change from "standard," and what were your impressions -- did you keep it that way? I was reading a good archived article through the Recumbent Blog about the resultant effect of keeping the knee bend at or below 90 degrees by doing this... And here's a guy (Mark Stonich) who makes/converts them... http://bikesmithdesign.com/Short_Cranks/short_cranks_faqs.html PB |
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Title: Re: Gettin' cranky... Post by aikigreg on Mar 7th, 2008, 10:11am I had 165s on my p-38, and I raced/toured on a trike with 155s two years ago. Really short cranks feel funny for a while, but you getused to them really quickly. I can't say that I ever felt any benefit from them, but I can't say I saw any performance decrease, either. I was plenty fast on both bikes. I do think, and this is just my .02 with no data to back it up, that most bent riders want to stay in the 165-170 range. I think you run a risk of torquing the knee at 175 or above, and I haven't seen the benefit to anything below 160. I want the crank to be long enough to get me up the hills. My knees are always the first indicators of stress for me - especiallybeing arthritic as I am, which is why i was so happy to get q-rings on my tica. That, much more than a set of cranks, cooled down the knee pains I had previously experienced, and I firmly believe that they are worth double their price in that regard. Best money ever spent, IMO. Much more important than a few crank millimeters. |
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Title: Re: Gettin' cranky... Post by FlyingLaZBoy on Mar 7th, 2008, 10:40am One of the corroborating knee-angle theories that was advanced in this other article (that I can't re-find at the moment) was a comparison to weightlifting -- you can lift more weight through a partial squat than you can through a full squat... (which may not mean 'squat' :D ) |
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Title: Re: Gettin' cranky... Post by aikigreg on Mar 7th, 2008, 12:31pm FlyingLaZBoy wrote:
That may be true for nancy-boys, but not for anyone lifting real weight. Given that I usually work up to a 450 pound squat for a week a year (you can't keep it there without overtraining and risk), I know for sure that if you try to stop that load short, you will tear something. However, go the full distance and your bones act like levers and the weight comes right back up with no strain on the joint itself. Now if by "squat" you mean dipping two inches like most fools I see in the gym, I'm sure my total would be closer to 650. ;D The idea of knee angle just doesn't apply when it's the femur and the other leg bones acting as levers to move a weight in only one plane of motion. Totally unlike a cycling stroke. |
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Title: Re: Gettin' cranky... Post by Richard on Mar 7th, 2008, 4:17pm I got to reading about techinques of weight lifters to see if I could make correlations with biking. Veery complicated. Some sites list 40 different variables for really good lifters. I guess biking is just as complex. Does rely heavily on quads though. Heres some numbers for not so nancy boys. The heaviest snatch of all time is 216.0 kg (476.2 lb), lifted by Antonio Krastev of Bulgaria in 1987. The heaviest clean and jerk of all time is 266.0 kg (586.4 lb) lifted by Leonid Taranenko in Canberra, Australia on November 26, 1988. |
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Title: Re: Gettin' cranky... Post by aikigreg on Mar 7th, 2008, 7:23pm Those are some tough lifts. I can't even do them with my crappy grip, but some of the kids I coach can hit over 300 on a snatch, military 205, and squat well over 400. The hormones in the beef are really doing some wonders! |
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Title: Re: Gettin' cranky... Post by Bud_Bent on Mar 7th, 2008, 9:49pm I won't claim to be an expert on short cranks either, but it seems to me the people who derive the most benefit from them are the people who have knee pain from the amount of knee flex longer cranks cause them to have to do. I never have had that kind of pain, so I've never had to urge to experiment with short cranks. |
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Title: Re: Gettin' cranky... Post by aikigreg on Mar 7th, 2008, 10:10pm exactly. I think the best situation is the longest crank length that's right for you. Which for most of us is 165-170. |
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Title: Re: Gettin' cranky... Post by FlyingLaZBoy on Mar 11th, 2008, 9:46pm The Stratus XP comes with a TruVativ Rouleur crankset with 175s... But it also has an "external" BB, which according to a recent BROL thread, creates problems when wanting to shorten cranks... I'm not quite sure why... But the shortest cranks TruVativ makes are 165s... Any thoughts as to why -- I don't really know the diff between "internal" and "external" BB mechanisms and crank attachments... |
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Title: Re: Gettin' cranky... Post by aikigreg on Mar 11th, 2008, 10:24pm The problem stems from the fact that these designs are essentially hollow crankarms - therefore you can't shorten them. Shimano hollowtech is an example. There isn't a real bottom bracket to speak of. Hollowtech is of the devil, IMO. sell it off and buy a nice standard square taper or isis BB and have mark stonich make you some arms. |
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Title: Re: Gettin' cranky... Post by Opus the Poet on Mar 12th, 2008, 1:46am Or just go to Gaerlin and buy some BMX cranks and some tripleator chainring bolts, or a Salsa tripliser ring that lets you attach a Granny ring to your small ring. Opus |
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Title: Re: Gettin' cranky... Post by FlyingLaZBoy on Mar 12th, 2008, 10:11am Got this reply from Mark Stonich, about shortening the TruVativ 175s.... <<<I should be able to shorten such cranks in the near future. The problem isn't the external BB but the fact that the spindle is permanently attached to the right arm. This is a problem with my current fixture and standard tap holders. I know what needs to be made to allow shortening your 175 cranks. First I need to determine several critical dimensions on this new type of cranks. Then I need to find time to make the new tooling. Finding time is a big problem.... And I am busier than ever shortening the cranks that can be done with my current tooling. Mark Stonich; BikeSmith Design & Fabrication 5349 Elliot Ave S. - Minneapolis. MN 55417 Ph. (612) 824-2372 http://bikesmithdesign.com http://mnhpva.org >>>>>> |
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