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Technical Q&A with Lennard Zinn - Crank issues galore

Published: Nov. 1, 2005
Technical Q&A with Lennard Zinn - Crank issues galore
Technical Q&A with Lennard Zinn - Crank issues galore

Realistic test?
Dear Lennard,
Your recent response on Velonews.com regarding Shimano’s new HollowgramII bottom bracket mentioned VeloNews’ (print edition) crankarm stiffnesstest. I must have missed that one, but it did bring to mind a persistentquestion that I have: Can the average mortal – or pro for that matter –actually flex a quality crankarm, especially considering the planes offorce being applied?

It seems to me that what riders’ interpret as crankarm flex is muchmore likely to be frame and BB flex. I’m not an engineer, but it seemsimpossible for a human to apply the power through a pedaling action thatwould be required to flex a crankarm in a plane along its main axis (i.e.,BB to pedal).
PeteFrom the test engineer who performed the tests

We ran several tests at Schwinn and GT where we had ridersof all sizes sit on exercise bikes and pedal against loads. We also rantests where the chain was clamped to the frame of the machine. The firstperson we tested was a National-caliber track rider (he actually has anational championship in pursuit) we were all floored when he could easilyhit 800 lbs. When he actually tried he could hit 1000 lbs. Most of ourtesting was based on an old Schwinn standard and none of us were presentfor the original testing so we wanted to be sure that the test standardwas valid. It's valid.The loads I used (in the VeloNews Vol. 32/No.19 November10 2003 "Black Gold") were in the maximum 250-pound range to test crankarm stiffness, and I feel that most people given the right conditions couldfeel the difference between the stiffest crank and the least rigid crank.Many of the cranks were so close in rigidity that it would be tough totell any difference. Larger and stronger riders would be more likely tonotice a difference since they will apply higher forces. As far as whetheryou could tell the difference between a flat tire and a flexible crank,well let's just say I'd be keeping my tires inflated!

Mark Rhomberg
Bike Testing, Inc.

The precedent
Dear Lennard,
I just want to put in my $.02 worth regarding comments you made inthe magazine about the S-Works FACT carbon crankset. These cranksare closer in comparison to www.negmass.comcranks than to Kent Carlson's Sweet Parts cro-moly cranks! The Sweets arelike Roger Durham's Bullseye cranks, asymetric and steel! They don't fastenin the center, or use the same type splines. If only the Isis type splinewas around when Kent was making his Sweet Wings, the cranks might stillbe manufactured today!
T.G.Dear T.G.,
Actually, that is incorrect. The Sweet Wings, while they are completelymade of cro-moly steel as you said, do indeed fasten in the middle. Eacharm has a partial-length hollow spindle attached to it with a male splinedend on one and a female splined end on the other. There is a short boltthat you reach with a long 8mm hex key that holds the two together. I actuallyhave three sets here still, and I just snapped this photo of them. I haveno more non-drive-side cups for them, since people have begged them offof me over the years, so I can no longer install them. They were way aheadof their time with oversized bearings and integrated, oversized spindles.
LennardTriple or compact?
Dear Lennard,
I am a 6-foot tall, 200-pound rider. I have been riding for thepast seven years at a competitive club level. I have huge power onthe flats and time trialing, but hills are my weakness, thus I have beenactively working on my climbing skills. I have been playing withgear combinations, but still haven't gotten it right. Currently Iam riding a 53/39 - 12/27 with 172.5 cranks. I bought the 27 afterhaving an average cadence of 50rpm going up a local climb. Afterattempting the same climb on a 27, my cadence improved to 60-65rpm.I am considering either an FSA compact or a triple. I have read yourgearing chart and articles on VeloNews and wanted to confirm thatyour advice would be the compact. Is this true?
CameronDear Cameron,
Yes, that’s true.
LennardYou know what they say about guys with big feet
Dear Lennard,
I'm 6 foot 8 and have experimented with longer crank arms in the past- I think they were 190mm. One of my issues was my right foot was reallyclose to and would occasionally hit the rear derailleur. What can I do?
MarkDear Mark,
That can be a problem, but it is remarkably rare. I find that mostriders, even with size 14 feet on a 215mm crank, do not hit the rear derailleur,even with a short chainstay on their frame, if the bike fits them. Thatis because the ankle rotates in the vertical plane (the toe points down)as the foot pulls up on the backstroke, and it clears the derailleur. Thisis why triathletes with super-short chainstays and 26-inch wheels do nothit their heels, nor do most riders on short-chainstay time-trial bikeswith seat-tube cutaways for the rear wheel to tuck into.One problem can be that if your saddle is too low, your ankle will beflexed too much on the backstroke, and it will hit. This is often a problemwith somebody your height, because most bikes you can find will not allowyou to raise your seat enough to reach full leg extension, even with anextra-long seatpost. Also, if you are using toeclips, your feet are likelytoo big to go as deeply into the pedal as they should be, so your heelsstick out further back.I think that you will find that anyone with big feet, no matter thecrank length, can hit the rear derailleur with their heel if their footis flat. Back in 1980, I totalled a wheel and rear derailleur by bunny-hoppinga train track on a Masi Gran Criterium. My right foot was back and levelas I jumped, and my heel pushed the derailleur into the spokes, stoppingthe wheel in midair. When I landed, metal parts flew everywhere, and mywheel was D-shaped from the spokes mangled by the derailleur pulling therim in. That was with a 180mm crank, but I had never hit the derailleurwhen pedaling, and now I do not either, even though I ride a 205mm crankand have size 12 feet and 41cm chainstay length. I have a lot of overlapwith my rear derailleur, but I never hit it when pedaling. And it is notthat my heel clears to the outside of the derailleur; my heel is prettyfar in toward the crank (i.e., more duck-footed than pigeon-toed); it clearsforward of the rear derailleur by rotating forward. I am more careful jumping,though! I try to bunny-hop my bike with my right foot forward.With a bike that fits you properly (which admittedly is a challengefor people your or my height – that’s why I started building custom framesand custom cranks!), if your foot still hits, then you need either a longerchainstay on the frame, or you need a wider pedaling stance. Moving yourcleats inboard on the shoes would be the first thing to try. After that,a longer pedal spindle or longer bottom-bracket spindle may be required.
LennardSimple Green follow-up:
Dear Lennard,
I am a fan of your repair books and I read the column often. Whilereading this weeks edition, I noticed that you mentioned Simple Green causingchains to crack after prolonged exposure. I can substantiate this. I tookmy PC-1 chain off of my track bike and dunked it into a 2-liter filledhalfway with undiluted Simple Green. Since I was replacing the chain, Ifigured I would just clean the old one and stick it in my toolbox for futureprojects. I shook the bottle for a bit, then put it on the windowsill tosoak for a while.Five months later, I cut open the forgotten bottle to use the chainon my cruiser/fixed-gear hack job. After rinsing the chain and puttingit together, I noticed hairline cracks in the plates of the chain. WhenI used a chain breaker, the link crumbled.
So the SRAM rep was right; Simple Green will cause chains to crack.
DavidDear Lennard,
Aha! I can vouch for this problem. I left a SRAM 9 speedchain submersed in Simple Green for, oh, about two weeks (two small childrenis my official excuse). Ten miles into the first ride after re-installingit I stood up to climb a small hill and it snapped. The chain actuallybroke at the plates, not the pin. I'm not a big guy and don't producethat much torque--I've never broken a chair before. So this revelationfrom the SRAM rep makes sense.
Doug

Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of several books on bikes and bike maintenance including the pair of successful maintenance guides " Zinn & the Art of Mountain Bike Maintenance" and "Zinn & the Art of Road Bike Maintenance."Zinn's regular column is devoted to addressing readers' technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.