Technical Q&A with Lennard Zinn – Chains, cranks and cutting carbon
Questions about cutting carbon, shifting problems, chain length and more
Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.
By Lennard Zinn
My new bike – with Ultegra 9 STI double chainring – was having someshifting problems. Troubleshooting the problem I noticed my chain lookedto be too long compared to my friction shifting bikes. I referred to yourbook (Zinn& the Art of Road Bike Maintenance, ) on chain length. In doingthe set up in your book, my jockey wheels did not align vertically; mychain was longer.I carried my bike to the shop to question the length and shifting problem;and was told that the length of that set-up did not apply with the newshifting systems of today. My question; is this set-up correct for length;if not; what is the correct set-up to determine length?
With double cranks this still applies, except if you have an extremelylarge rear cog (bigger than a 27), in which case, go big-to-big and addone extra link, as you would with a triple crank.
LennardOne over the other?
I have used a standard crank setup and a compact setup for climbinga local hill (18K with 1080m vertical). I stand a lot and on thecompact to get a smooth steady rhythm while standing I shift to my 34/23which is 39.9 gear inches. When using my standard 53/39 I stand anduse my 39/27 and 39/25 – 39 and 42 gear inches – which feels good.There seems little difference when standing as a matter of fact thehigher gear inches “feel” okay. So given that a bike can achievealmost the same gear inches (39x 27) versus (34 x 23) is there any mechanical advantage to using a bigger front chainring (39) over the smaller 34 chainring?
No, there is not.
LennardThat delicate cut
What is the preferred method for cutting a carbon steerer tube, hacksawor tubing cutter?
When cutting a carbon fiber steering tube, cut 3/4 of the way throughwith a hacksaw and then turn the steerer over and cut from the other sideto meet your cut. This will prevent you from cutting right through andpeeling back the last few layers of carbon at the bottom. Make your cutstraight. Measure twice; cut once! Mark it straight by wrapping a pieceof tape around the steering tube and cutting along it.
LennardThrow caution to the wind
Is there any kind of way to remove the crank arm (right side) if theextractor threads of on the crank arm is gone? My bottom bracket needsreplacing but I can’t remove it because I can’t remove the crank arm.
Given its current condition, you aren’t trying to save it for futureuse, so try prying it off with a claw hammer.
I recently bought a 2004 Cannondale R2000. I love everything aboutthe bike except that occasionally when I’m climbing in a seated positionmy right heel will hit the chainstay with each pedal rotation. I’ve beencycling for years on several other bikes and have never had this problembefore. In comparing this bike to my other bikes, there is barely a millimeterof clearance between my shoe and the chainstay even when my foot is perfectlystraight.I’m sure that the contact is caused by my pulling in my heel as I pedal(although I have a pretty standard pedal rotation), but I’m wondering ifthere’s anything I can do to increase the clearance between my heel andthe frame in that place? I use standard Look pedals and wear Specializedshoes, size 45.Are there different pedals that would help? A wider bottom bracket orcrankset? Any insight you could provide would be much appreciated!
You can put a washer or two between your pedal and your crankarm. Ifthat does not do it, you could use a wider bottom bracket.
LennardFeedback from previous columns
One thing that Mr. Calfee left out his letter regarding carbon postslippage in your January9 column is the static coefficient of friction effect.
F= uN where F is the frictional force, u isthe static coefficient of friction and N is the normal force. I’msure it is known but I think that the static coefficient of friction fora carbon seatpost is low compared to a metal post. This exacerbates theslipping problem considerably.
I just read your storyabout winter training and using Dartfish Video Analysis Software.The article was fantastic. I have been using Dartfish for cycling and othersports for some time now. The software is great for analysis (biomechanicsand technique), but just as beneficial for communicating to my athletesabout their technique. I use it for rider positioning, rider technique,tactics, and training. I hope to be working with junior riders thissummer with Steve McCauley and USA Cycling. See my website, www.velosmart.comor my blog, www.halloffameproductions.blogspot.comfor more about Dartfish.
Gregory M. Combs, Ed.D
Velo Smart Coaching
Technical writer Lennard Zinn is a frame builder (www.zinncycles.com),a former U.S. national team rider and author of several best-selling bookson bikes and bike maintenance including Zinn& the Art of Mountain Bike Maintenance, which is now availableas a 4-hour instructional DVDZinn& the Art of Road Bike Maintenance, and Zinn’s Cycling Primer:Maintenance Tips and Skill Building for Cyclists. Zinn’s regular columnis devoted to addressing readers’ technical questions about bikes, theircare and feeding and how we as riders can use them as comfortably and efficientlyas possible. Readers can send brief technical questions directlyto Zinn. Zinn’s column appears here each Tuesday.