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Technical Q&A with Lennard Zinn

  • By VeloNews.com
  • Published Feb. 18, 2003

By Lennard Zinn

I have a new pair of Sidi shoes and am considering going from Lookpedals to either Campy Record Pro-Fit Plus or Shimano DuraAce SPD-SL’s.Which, if either, will work better with the Sidi sole and plate? Will I need to get longer cleat bolts for either system?  Will I needto use the Sidi plate with either system?How about Sidi with Ritchey Road pedals?  (I understand the Ritcheycleat is a 2-hole SPD style.) –PhilDear Phil;
For the Campy or new Shimano SPD-SL pedals, you will use the sameSidi plate you did with the Looks, and both pedals will work identicallywith that shoe as the Looks did. The screws that come with the cleats willwork fine.
Ritchey makes both SPD and SPD-R pedals, and separate Sidi adapterplates for each system exist (different from your three-hole Look-styleplates). –LennardLegal or not?
Dear Lennard;
I’m using Easton EC 90 handlebars on my road bike and am very satisfiedwith them. My question is this: later this year I’m participating in a12-hour challenge and would like to add aero bars since drafting is notallowed in this event. I’ve been told you can’t use aero bars on thesehandlebars or on any carbon fiber bars. Is this true? –LorenAnswer from Easton:
Loren, yes, it is true.  Do not use clip-on Aero bars on Easton’scarbon fiber road bars. Or on any lightweight road bar in aluminum or carbonfor that matter. The clamp design on Aero extenders are generally of poordesign. Most of these clamps are not round in design and therefore forcethe bar into an oval shape when torqued to the proper values. This is notgood for a handlebar and can lead to breakage. If you want to use Aeroextenders you need a heavier bar closer to 300 grams.
–John Harrington
Easton SportsThe long and the short of it
Dear Lennard;
I’m sure you’ve come across people who are blessed with having a shortand a long leg.  Mine are acting like that because of a problem I’mhaving with my S.I. joint, so it’s getting fixed on me.  However,what could someone do to minimize the effects of disproportionately longlegs?  Shim their pedals?  Shave one side of their saddle? –DevinAnswer from Andrew Pruitt, director and founder of the Boulder Centerfor Sports Medicine:
Devin, there are two kinds of leg length discrepancies (LLD), structuraland functional. The structural are real and are found in the long bonesof the leg and can be measured accurately with an x-ray or close with atape measure by a qualified person. The functional kind are can be foundin lots of places, like one foot more flat than the other, one knee thatis worn out, a hip or knee that doesn’t bend like the other one, or likein your case a pelvis twist. Physical therapist are very good at findingthese functional LLDs.The easiest way to compensate for a tibial (shin) LLD is with a shimbetween the cleat and shoe. I usually shim for 1/2 of the known tibialLLD. The easiest way to compensate for a femoral (thigh) LLD is with acombination of cleat/shoe shim and asymmetrical foot shift, with the longleg foot going forward and the short leg foot going back. Let us say theyou have a 8mm femoral LLD, I would start with a 3mm cleat/shoe shim andthe long leg foot forward 1mm and the short leg foot back 1mm. This givesyou approximately 1/2 compensation. Femoral LLD compensations are a workin progress until you find what feel the best for you, I always suggestthat they ride each variation for at least a week or approximately 200miles.It is not always this easy as many people have LLD that are a mixtureof tibial, femoral and functional. If after several trials you can’t findsomething comfortable, you better get some professional help from a medicalperson who knows bicycle positioning. The suggestions noted above can befound in my book, Andy Pruitt’s Medical Advice for Cyclist as well as HighTech Cycling, edited by Ed Burke, PhD. You can find my book at www.roadbikerider.comand Dr Burkes thru Human Kinetics Publishing and VeloPress.Best of Luck,
Andrew Pruitt, Ed.D
Founder/Director
Boulder Center for Sports MedicineAnother question about leg length discrepancies
Dear Lennard;
I recently noticed that you directed a VeloNews reader to TomSlocum at High Sierra Cycle (hscycle.com)for non-standard length crankarms.I wonder if you are aware of Tom’s service, which claims to help thosewith leg length discrepancies.  I bought in to the claims a year anda half ago and have had little improvement during that time despite many”adjustments” using a combination of a special crankset, experiments withdifferent length crankarms, positioning shoe cleats in various places,and shims placed between the shoe and the cleat, and putting the crankarmoff top dead center by various degrees in both directions.  I’m prettyfrustrated and I’m wondering if you’re aware of any standard “fixes” forthis problem, or if you are familiar with Tom Slocum’s approach. I only have 1cm or so discrepancy, which doesn’t seem like it should bethat hard to fix. –Anne GregoryDear Anne;
I have no personal experience with Tom Slocum’s “Leg Equalizer System”to compensate for leg-length discrepancies. I have written articles aboutit in VeloNews (May 8, 1995) and Inside Triathlon (July 95). At the time,1984 Olympic road champion Alexi Grewal told me he used it and loved it.See Andy Pruitt’s letter above for a more standard approach. –LennardDear Lennard;
I am a heavier rider, in the 230lbs range.  I try to maintaina cadence in the 90+ range and in the 100′s if I put my mind to it. Eventually though, I end up with shredded hubs, broken spokes and crackedrims.  I have broken Mavic rims, carbon spokes, straight-pull spokesand don’t get me started on my year with the Spinergy SR-3′s (or what isleft of the back one.)  I need a back wheel that can take a 25-28mph pace line, stop light starting sprints to 25+ and mashing up 1/2 mileclimbs out of the saddle.  You are the Zinn Master, please guide meto the light.–GregDear Greg;
Try Mavic Ksyrium SSC SLs. I have sold dozens of pairs of thoseto customers a lot heavier than you for the past two years, and I haveyet to hear about a single problem from any of them. –LennardMore on stuck seatposts:
I too had a titanium seatpost frozen in a Merlin XLM.  As theframe was broken I sent the seatpost in the frame back to Merlin. They clamped the seatpost in a vise and twisted and pulled on the frameuntil the post came out, mauling the seatpost clamps in the process. Merlin no longer uses the magnesium inserts that are the root cause ofthis problem.  As any damage appeared to be only aesthetic, I reusedthe seatpost on the replacement frame.  Six months later the seatpostsnapped and sliced open my leg.  I spent a week of my bike vacationtrying to ignore the seven surgical staples attached to the inside of mythigh.  For anyone concerned, the cut was six inches above my kneeand I’m intact.  Had it been my road bike seatpost that failed I mightnot be.Since I’m an engineer I’ll take this opportunity to preach about materials.Some materials fail gracefully and some fracture.  Steel is very tough,ductile and highly fracture resistant.  Steel parts rarely fail instantaneously. Carbon fiber parts typically parallel steel’s slow degradation.  Aluminum,and to some extent titanium, are fracture susceptible.  Fracture isan extremely rapid degradation of a structure.Fracture can be caused by an undetected flaw in the part, by an accumulationof fatigue cycles or by a single energy event.  Fracture is extremelyundesirable in some bike parts; handlebars, stems and forks for example. The takeaway from this is don’t set yourself up for a fracture inducedinjury.  All materials choices are compromise of strength, weight,durability and cost.  Just because it costs more doesn’t mean it willlast as long.  In my case I should have followed the manufacturersinstructions and replaced the seatpost after one year.  Change yourlightweight aluminum parts before they fatigue.  Select a carbon fiberor steel fork over an aluminum one.  Wear your helmet, your next crashmay not be caused by pilot error.–John


VeloNews technical writer Lennard Zinn is aframe builder, a former U.S. national team rider and author of severalbooks on bikes and bike maintenance including the pair of successful maintenanceguides “ Zinn& the Art of Mountain Bike Maintenance” and “Zinn& the Art of Road Bike Maintenance.”Zinn’s VeloNews.com column is devoted to addressing readers’ technicalquestions about bikes, their care and feeding and how we as riders canuse them as comfortably and efficiently as possible. Readers can send brieftechnical questions directly to Zinn.Zinn’s column appears each Tuesday here on VeloNews.com.
 

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