Technical FAQ: Shorter legs with age, lighter cranks, 10s/11s crank compatibility, and decreasing drivetrain wear with chain waxing
Shorter legs = lower saddle, lighter cranks = less energy spent
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Having read your columns on bike fit for older riders, I’ve recently discovered another area that needs attention — leg length. Unlike some of your correspondents, my leg length has decreased by at least an inch as I’ve aged — I’m now 75.
Back in 2011, I developed Piriformis Syndrome (PS) and was having quite a time in overcoming it. I mentioned that to Steve Hogg, a professional bike fitter writing at the time for an online Q&A section of CyclingNews. Among other things (PT, stretching, etc.), he suggested lowering my saddle, which solved a number of problems: knee pain, foot alignment, and the PS. I kept the lower saddle height, and the PS and other issues went away.
I recently developed PS again and was without comfort from the usual treatments (PT, injections etc.) when the light bulb went off — I had lost some leg length over the years from Osteoarthritis and was probably riding too high. I’ve lost height in my spine and the inseam measurement on my long pants had declined by at least an inch. I was stretching to touch the ground with my toe. So, I gradually dropped my saddle by 3cm, and the PS is slowly resolving itself. My dicey knees also feel better, and I don’t strain to touch the ground when I stop. The lower saddle has also reduced my forward reach and I’m also more comfortable in the saddle. It seems that everything needs to be re-evaluated with age.
This makes sense. Losing leg length over time hadn’t occurred to me. I always thought old people became shorter just because of losing length in their spines, though I wondered how that alone could account for how tiny many of them become.
In my case, I am at least two inches shorter than I was 45 years ago. I had attributed that entirely to decreased spine length, and all of the aging adjustments I have made to my bikes have been in the cockpit—reducing reach and increasing stack of the handlebar position. My x-rays show that the space between my lumbar vertebrae has gone almost to zero (the discs have flattened), and the bottom of my rib cage is consequently much closer to my hip bones than it used to be. I figured that accounted for the entirety of my loss of height; your letter had me question that, so I just now measured my leg length to see if it has decreased. It still measures the same 96.7cm (38 inches) that it has my entire adult life, so this leg-length reduction has not so far gotten to me at age 64 (as of a few days ago).
I have many friends whose knee-joint cartilage has deteriorated with age, often resulting in increasing bowlegged-ness (is that a word?). In that case, it’s clear that a leg-length reduction has occurred, mandating lowering the saddle, perhaps even after total knee replacement.
In an effort to try to determine where money is best spent on an upgrade, I wanted to ask about rotational weight when it comes to the crank. It’s been drilled into our heads that rotational weight with regards to wheels is far more important than non-rotational weight. The crank set is rotating and being pushed by our leg strength. Does a difference of 100–200 grams for this matter? I am 60-years-old and have maintained good fitness, but I’ll take any benefit since I’m not getting younger.
Whenever going uphill, weight reduction on the bike reduces energy cost, and each gram of it grants the same energy savings, whether it is rotating weight or weight of non-moving parts. Reducing rotational weight of cranks (as well as of rims, tires, tubes, spokes, pedals, and shoes) saves more energy than static weight on the bike only when the bike is accelerating after hitting the brakes; otherwise, you get that energy back when the bike is decelerating.
I go into this in detail here when discussing whether there is a benefit to climbing with lighter “climbing wheels” vs. deep-section aero wheels. I also describe how the fact that nobody maintains the same angular speed of the foot everywhere around the crank circle doesn’t affect this calculation of relative benefit of rotating weight vs. static weight, unless the brakes are applied.
In answer to your question, probably the instance where rotating weight makes the most difference, whether it’s in your crankarms or in your rims, tires, shoes, or pedals, is in cyclocross, due to constantly braking into corners and accelerating out of them. A criterium race has similar frequent braking into corners and accelerating out of them. However, unlike the case of deep-section aero wheels vs. lighter, shallow-section wheels, where the aerodynamic benefit of the deeper wheels in a criterium will still overwhelm the cost of the added weight, the lighter crank will always save energy (assuming the two cranksets are of similar shape and stiffness) in a crit.
On riding without braking, though, whether on the flat or on hills, a gram of weight savings in your crankarms will have the same effect on your speed as a gram of weight savings in your frame, fork, saddle, handlebar, etc. Lighter cranks are still worthwhile in that case — just no more worthwhile than lighter parts anywhere else on the bike or rider.
[I’m] looking to upgrade to an outboard [bottom bracket] system. I am currently running an FSA carbon elite [crank] with the Octalink interface. With 10-speed and high-end cranksets and bottom brackets going by the wayside, [I] must upgrade. Is it possible to run, let’s say, a SRAM Red 11 GXP crankset in place of the old 10? Do you think the Campy 10 front derailleur would run satisfactorily? Any suggestions would help.
Yes, the 10-speed front derailleur will shift fine across the 11-speed chainrings.
In regards to the question from Loren regarding benefits of chain waxing, I believe the most compelling reason to wax for recreational cyclists is the reduced drivetrain wear and associated cost savings that accompany not replacing chains and cassettes as frequently. You alluded to this regarding a waxed chain not picking up grime, etc. while riding — the testing from Zero Friction Cycling does a great job of illustrating this effect over longer term use.
Anecdotally, after switching to hot-waxed chains I saw my MTB and gravel bikes go from replacing chains twice a season and cassettes once a season, to having chains and cassettes last multiple seasons despite increased mileage. While the watts saved are a nice bonus, the cost savings (and silent drivetrain) are the real motivation for me to continue waxing all my bicycle chains.
Thanks again for all the knowledge you’ve shared over the years!
Very important point you make. Thanks.
Lennard Zinn (https://www.velonews.com/byline/lennard-zinn) , our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (Error! Hyperlink reference not valid.>) and purveyor of non-custom huge bikes (Error! Hyperlink reference not valid.>), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, 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 in physics from Colorado College.