Gear

Technical Q&A with Lennard Zinn: How big is that little ring?

Dear Lennard;I am considering changing my Dura Ace triple back to a double. I noticedthat FSA now makes a Carbon Pro Compact Crank with a 34/50. It would seemthat this combination would give me gearing that would benefit me duringthe "mountain" centuries that I enjoy. Any thoughts on the pros and cons of having a 34/50 crankset?PaulDear Paul;I just got one of these FSA cranksets myself to try out and ordereda Pinarello one as well. I have been intrigued by them ever since FaustoPinarello, who originated the modern incarnation of these size rings, ravedto me a couple of years ago about riding

By Lennard Zinn

Dear Lennard;
I am considering changing my Dura Ace triple back to a double. I noticedthat FSA now makes a Carbon Pro Compact Crank with a 34/50. It would seemthat this combination would give me gearing that would benefit me duringthe “mountain” centuries that I enjoy.
 
Any thoughts on the pros and cons of having a 34/50 crankset?
PaulDear Paul;
I just got one of these FSA cranksets myself to try out and ordereda Pinarello one as well. I have been intrigued by them ever since FaustoPinarello, who originated the modern incarnation of these size rings, ravedto me a couple of years ago about riding in the mountains with them.It makes a lot of sense to me to use a 110mm bolt circle instead ofa 130mm or 135mm one. With a Campy 10-speed medium-cage rear derailleur,you can use a 29-tooth cog, and a 34-29 can get a road bike up almost anything.On the other end, you need a different cogset if you care about going downhillfast, since a 50-13 does not cut it.If you consult a gear chart, you will see that a 50 X 11 gear is biggerthan a 53 X 12 (or a 54 X 12, even), and a 48 X 11 is between a 52 X 12and a 53 X 12. On the low end, a 34 X 23 is lower than a 39 X 26, and a34 X 25 is lower than a 39 X 29! These are very low gears, yet the cogsand crank are lighter than a double and far lighter and easier to shiftthan a triple.Are you aware that Tyler Hamilton and Carlos Sastre were using FSA compact-drivecranks during their Tour de France stage wins this year? CSC team directorBjarne Riis was initially resistant to having the team use them. Riis ultimatelyrealized that the team’s domestiques, after they had done their hard pullsin the mountains for the team leaders and had been dropped, could makeit to the finish over the final mountain passes with less strain by havinglower gearing. And for Hamilton, it was a blessing having a lower gearand not having to pull so hard on the bars with that broken collarbone.
LennardLogic would suggust that…
Dear Lennard,
Would placing the cycle computer magnet closer to the front wheel axlegive a faster revolution reading than if it were placed nearer the rim?
RickDear Rick,
No. Every point on the wheel turns at the same RPM.
LennardPitch?
Dear Lennard;
I am in the process of setting up a fixed gear bike for road training.I have always heard that track chains have a 1/8-inch pitch while roadchains are 3/32-inch however, I have never known exactly what that means.To what does this measurement refer? Is there a difference between thecogs/rings of a track bike and a road bike? Must all the components offixed drive train match with respect to these dimensions? Is there a significantadvantage for either one if I’m never going to actually be on a velodrome?I’m ready to start spinning, so whatever advice you could offer on thesubject would be greatly appreciated.
JonathanDear Jonathan,
You are referring to the width of the cog and consequently of the chainroller, i.e., the width in between the inner chain plates. Most track cogsare 1/8-inch thick, while road cogs are thinner – 3/32. Yes, the chainring,cog and chain must all be on the same standard or parts will either notengage or will wear out quickly due to excess slop. The thicker chain,chainring and cog are stiffer and stronger for use on the track as wellas for many BMX and cruiser bikes (there is an even thicker standard onsome BMX and cruiser bikes, namely 3/16-inch). Some track pursuit bikesuse the thinner, 3/32-inch chain, chainring and cog since the forces arenot as high and weight is a consideration. For your purposes, there isno need for the 1/8-inch system.The word “pitch” can be a bit confusing here, since any of you can probablythink of a half dozen meanings for the word in the time it takes to readthis sentence. In somewhat stilted mechanical speak, pitch is an intransitiveverb meaning to engage or interlock. As a noun, once again in mechanicalsystems, it means the distance between a pair of things. So, in the caseof chains, it can be confusing, because people sometimes speak about pitchas you have, meaning the distance between the chain’s inner plates. However,you can also talk about all of the bicycle chains we have been talkingabout here as being 1/2-inch pitch. In this case, it means that the chainrollers are 1/2-inch apart to mate with teeth that are 1/2-inch apart,thus also on a 1/2-inch pitch. (And you may have heard of the “thread pitch”in bottom brackets and threaded headsets.)
Lennard
 Feedback:
First, a little more on the Nov. 11 column on two- vs. four-bolt stemclamps with carbon handlebars. True Temper had actually sent this responseto the original question prior to Nov. 11, but I did not find it beforehandand consequently did not post it.I have given this much thought and I still can not think of any benefitsof two-bolt clamps regarding safety. In fact I am strongly convinced thata four-bolt clamp is a more secure device and provides a higher degreeof safety than a two-bolt design. A four-bolt design has better (more even)stress distribution over the surface in contact.Also, the load is shared by four bolts, so if one were to come loose,the other three can share the load. On a two-bolt clamp, when one boltloosens, the bar will slip. I have had this happen on three occasions onmy road bike with a two-bolt faceplate.Based on computer modeling and lab testing, we have found that carbonfaceplates with four bolts are much stronger. Two bolts concentrate toomuch pressure in the center of the clamp.Below is further clarification from one of our engineers.
Bert Hull
True Temper
 

I believe four bolts offer more clamp security because theyshould be able to distribute the clamping pressure more evenly and thebar will not slip if one bolt should come loose. Also, four bolts shouldprovide more stiffness in the bar/stem assembly.Claims about danger of four-bolt clamps are all about the relative stresslevels which some claim are induced in the bar by different stem designs.I cannot accept that this difference is inherent in two- and four-boltdesigns. It depends on the detail design such as the contact areas andthe tightening torque of the bolts. I would accept, however, that a numberof four-bolt stems effectively use two very narrow clamping “rings” aroundthe bar with the center section of the clamp being eliminated to save weight.This limits the surface area, and if the bolts are then over tightenedcould provide a crushing load that could damage the stem. This may be whatthe questioner was getting at, but it is not a condemnation of all four-boltstems. I still contend that four-bolt designs should be better, but theclamping area must be sufficient and the bolt torque controlled to preventdamage. I consider our clamp design to be a good one.
Graeme Horwood
True Temper

Finally, on last week’s crank length discussion
Dear Lennard;
I read your recent response to the most recent crank length questionand you pose some interesting points. Your experience on the road and fittingand building bikes is an important element to the whole equation, howeverthe ‘difficult studies’ you propose on the crank length question have alreadybeen done and published in peer-reviewed scientific journals. On the questionof commercially available crank lengths, it appears that both for maximalor submaximal power production, the currently available lengths[165mm-180mm]provide no difference[1,2]. I would submit that personal preference andminimizing injury risk should be greater factors in size selection, ratherthan any ‘hope’ of performance difference.
CD1. Martin JC, Spirduso WW. Determinants of maximalcycling power: crank length, pedaling rate and pedal speed. Eur J ApplPhysiol. 2001 May;84(5):413-8.2. McDaniel J, Durstine JL, Hand GA, Martin JC.Determinants of metabolic cost during submaximal cycling. J Appl Physiol.2002 Sep;93(3):823-8.Editor’s Notes:
The first of these two, cycling physiologist Jim Martin’s maximal efforttest is at http://www.ncbi.nlm.nih.go.It does not exactly say that the currently available lengths provide nodifference. It concludes that, “the optimal crank length was 20 percentof leg length or 41 percent of tibia length.” However, it does go on tosay that, “Even though maximum cycling power was significantly affectedby crank length, use of the standard 170-mm length cranks should not substantiallycompromise maximum power in most adults.”Today, the “spin like Lance” idea is not only in vogue but there arealso lots of cyclists who are convinced that it is unquestionably the best(and perhaps only) way to success. Against that backdrop, it is interestingto note that the second study, also Jim Martin’s, at http://www.ncbi.nlm.nih.gov,concluded that pedaling cadence “does not significantly contribute to metaboliccost.” Instead, foot speed, which you can maintain with any length of crank,was found to be one of “the main determinants of metabolic cost duringsubmaximal cycling.” High cadences are unrealistic with super-long cranks,just as low cadences make it hard to get anywhere with super-short cranks,but you can always still attain the same foot speed with any length crankas, say, the foot speed associated with riding a 170mm crank at 90rpm.
Lennard


VeloNews 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.