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Technical Q&A with Lennard Zinn – Lots and lots of follow-up

  • By Lennard Zinn
  • Published May. 22, 2007
  • Updated Aug. 29, 2010 at 10:38 PM EDT

By Lennard Zinn

Side steppin’
Dear Lennard,
Regarding your April 10, 2007 article “Whatis it?“, I was wondering if you had any thoughts or opinions on modern-daypedal systems which are attempting to bring the ball of the foot directlyto where the pedal spindle typically is. The two that cometo mind are SideMount pedal (SMP) of Pasadena, CA and VistaMagic X of France.
DavidDear David,
I have not used the Vista Magic X, but I’ve used Steve Lubanski’s SideMount Pedal and Tom Slocum’s HighSierra dropped pedal built into a Speedplay. Both of them feel absolutelyfantastic to pedal with; most riders would be amazed to feel the difference.I think nobody realizes the amount they are compensating with each pedalstroke for the offset of their feet above the pedal spindle until theytry a dropped pedal. Pedaling backward, for instance, illustrates how muchless awkward it is. The feet really feel at home traveling in perfect circles.A friend of mine who swears by them demonstrated how much more stable yourhand position is with them; you end up squirming around a lot less readjustingthe hand position with different pedaling loads.That said, I don’t personally use dropped pedals, and these are my reasons:

1. The stance width (a.k.a. Q-factor) is considerablylarger with any dropped pedal than with a standard pedal, because therehas to be room between your foot and the crank for the pedal to swing.Dyna-Drive was not as bad in this way, but it still had that problem toa certain extent. I tolerate a wide Q-factor on my mountain bike becausethere is no way around it, but I dislike it on a road bike.
2. The bearings are much more likely to be problematicthan on a standard pedal. All of the support of the pedal forces is carriedon a thin bearing, rather than being supported on two or more widely-spacedbearings. You can see this bearing hereand hereon pedals that mount on standard cranks.
3. Some systems will not work with a standard crank, and thisis a big downside for those of us who like to experiment with crank length,use a non-standard crank length, or use more than one brand and model ofcrank. The High Sierra and Shimano systems require completely unique crankarmswith a huge hole into which the pedal bearing system is installed. Housingthe bearings inside the crank prevented Dyna-Drive from having as widea pedaling stance as the other dropped pedal systems, but it had two setsof closely-spaced loose bearings inside of the arm that gave its usersplenty of trouble. And the High Sierra dropped pedal also goes throughcartridge bearings pretty fast and has a pedaling stance wider than Dyna-Driveand approaching that of the Side Mount pedal.
4. While the Side Mount’s little drawer-pull pedal is elegantlysimple, its cleat is large, heavy and clunky. Using it requires a verylong learning curve. I have used several generations of the pedal and cleat,and I never got used to not having a pedal big enough that I could easilyhit it with a stab of my foot starting up from a stoplight. Some generationsalso tended to pre-release pulling straight up under hard climbing or sprintingefforts out of the saddle, and then with such a tiny target to hit withmy foot to regain my balance – well, it was not a pretty sight.

My ideal pedal would be a dropped pedal with the same pedaling stance (ornarrower) than a standard pedal, and with bearings, as smooth, light, andlong-lasting as standard pedals. But as far as I can see, those designconstraints are mutually exclusive, so I’ll probably stick with my trustyold Campy pedals.
LennardRing change?
Dear Lennard,
I have a race to do with a rather large hill in it. 5km long, witha 10-percent grade.On the front I have a 53/39 and on the back I have a 12/25. Can I changethe chain ring on the front to make it a 53/36?
PeterDear Peter,
No, you cannot make that change without getting a different crank.A standard bolt circle for a 53/39 is 130mm (Shimano standard) or 135mm(Campagnolo standard). You cannot put a 36-tooth sprocket on there, andit should be obvious why not (the bolts would be above the teeth!). Youwould have to buy a “compact” crank with a 110mm bolt circle diameter tomount a 36-tooth chainring.
LennardRegarding last week’s question on shimmy
Dear Lennard,
I had a low-price road bike that shimmied. It was my towny bike andI decided to try a front drum brake hub on it to see if I would get betterbraking performance in wet conditions. With that heavy hub in front theshimmy problem went away. So I agree with Rolf that shimmying is relatedto weight distribution, but there are other options besides unweightingthe front end. I have stopped shimmy once it started by moving my upperbody lower and farther forward to add weight to the front wheel. Or, asyou suggested the last time this subject came around, clamp the top tubebetween your knees.I also recommend that your readers with shimmy problems check the rearend of the bicycle. I used to work in a bike shop and a woman brought abike in complaining of a shimmy problem that never used to occur. She hadnot made any component changes. We inspected the bike for quite a whilebefore we discovered a crack in one of the chainstays, near the dropout!I have also cured shimmies by truing or replacing out-of-true rear wheels.
LarryMore Shimmy
Dear Lennard,
I’ve been racing for 25 years and, until recently, I had never hada bike that shimmied at any speed. I now have two – a Giant TCR aeroand a Louis Garneau 8.0 TT. Both shimmy wildly to the point wherepeople who’ve seen it were sure I was going to crash. However, theconditions that set off the shimmy are fairly specific: Speeds around35-45 mph in combination with a crosswind of more than about 15 mph.The stronger the crosswind, the lower the speed at which the shimmy starts.I’ve had both bikes over 45 mph several times (and the Giant over 55 mph)in all kinds of wind conditions and with three different sets of wheelsand this shimmy only occurs when high speed is combined with a significantcrosswind. Frame geometry for the two bikes is quite different butthe materials of construction are basically the same: Aluminum aerotubing and aero forks. Both frames sizes are the equivalent of 58cm (I’m six feet tall, with a 34-inch inseam and I weigh 162 pounds).I believe that the large cross-sectional surface area of the aero tubingresults in crosswinds generating substantial forces on the frame.It would appear that these forces in combination with higher speeds – andperhaps my particular size and position on the bike – match up with a resonantharmonic frequency in the aluminum aero tubing in this frame size.I’ve recently noticed that many aero time trial frames now come with eithersquare top tubes or oval top tubes with the wider dimension being orientedhorizontally rather than vertically.I intend to get rid of my Garneau and replace it with a newer designthat has a square top tube and is not made of aluminum. I can’t affordtwo new frames so I’m hoping to address the shimmy in my Giant by replacingthe aero fork with one that has round tubing. Hopefully this reductionin cross sectional area and force produced by crosswinds will at leastincrease the speed at which the bike shimmies to speeds I won’t normallysee.In the meantime, given my shimmy problems, I was very happy to readRolf Dietrich’s alternative solution in today’s column regarding how tostopping a shimmy. Both of my bikes have compact-type frame constructionand there is absolutely no way I can apply the standard solution of pinchingthe top tube between my knees – I simply cannot make contact with the toptube with my legs due to the compact frame design. The only problem withRolf’s solution is if the bike starts to shimmy when approaching something(a stop sign, slower traffic, or turns) that requires stronger braking.I’ve had one wild shimmy set off by having to brake from 45 mph – in crosswinds- due to slowing traffic. The bike had been trying to shimmy forseveral hundred yards and I had managed to prevent it by shifting my weightrearward. Once I had to hit the brakes, the forward weight shiftimmediately initiated a shimmy.
LeifRegarding measuring relativebike positions
Dear Lennard,
When measuring saddle setback, I’ve found it much easier to place thebike with the front wheel touching a wall, then measuring from the wallto the tip of the saddle (call this X), then from the wall to the centerof the bottom bracket (call this Y). The setback is then X-Y in whateverunits you prefer.It’s easier to hold the bike vertical and make sure the front wheelis straight than it is to level the bike in a stand.
MikeDear Mike,
What a great idea!
Thanks,
Lennard


VeloNews technical writer Lennard Zinn is a frame builder (www.zinncycles.com),a former U.S. national team rider and author of numerous books on bikesand bike maintenance including the pair of successful maintenance guides”Zinnand the Art of Mountain Bike Maintenance” and “Zinnand the Art of Road Bike Maintenance” as well as “Zinn’sCycling Primer: Maintenance Tips and Skill Building for Cyclists.”

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 (veloqna@comcast.net)Zinn’s column appears each Tuesday here on VeloNews.com.

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: / / /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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