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Technical FAQ: Crankarm length versus BB height, long-spindle Eggbeaters, perspective and more

  • By Lennard Zinn
  • Published Dec. 25, 2012
With a heightened bottom bracket and longer crankarms, Zinn's saddle is no higher from the ground than it would be on a standard ’cross bike.

Editor’s Note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

BB height versus crank length

Dear Lennard,
Thanks so much for taking the time to go into such detail about your ’cross bike set-up. Being a tall ’cross rider (6’7”) myself that also builds and races his own frames (steel lugged), this article was fascinating and raised a couple of questions for me.

I’ve been trying to run longer cranks this season on my singlespeed (180mm), but I keep having issues with pedal strikes. My drop is fairly low (70mm) because I like the handling. I have heard conflicting advice about long versus short cranks — basically my question is: do you see a benefit to the longer cranks and how does the bike handle with such a high bottom bracket? How about remounting the bike with such a high bottom bracket (and thus higher saddle from the ground)?

My final question is on fit: I did a fit through the UC Davis sports medicine group (I live in Davis, California, and they are highly recommended). They adjusted my saddle more forward than I would have thought based on my frame design (I also use zero set-back Thompson posts)… What’s the best way to better understand frame design, trial and error?

Thanks again for the great article, and all the advice articles you write. Your bicycle repair books are my reference guides on my workbench. I greatly appreciate your advice.
—Jonathan

Dear Jonathan,
That is a common misconception that my saddle would be higher above the ground with a higher bottom bracket, even though I’m using longer cranks. Let me clear that up. I have 30mm-32.5mm longer cranks than most ’cross bikes come with, and I have an approximately 30mm higher bottom bracket as well (38mm drop — so 32mm higher bottom bracket than you have). So that means that the height of my pedal above the ground when it is at the bottom is about the same on my bike as on a stock ’cross bike with 172.5mm or 175mm cranks. Since I would ride with the same distance (seat height) from the pedal to the top of the saddle on either bike, it therefore follows that the height of my saddle above the ground is the same on either bike. The height of the center of gravity of the bike and me is thus the same on either bike, resulting in similar handling. And of course, remounting is identical, as the height of the saddle above the ground is the same.

“What’s the best way to better understand frame design?” Wow, what a huge question. A combination of learning through trial and error and gleaning information from knowledgeable people is the best path I can see.
― Lennard

Long Eggbeaters

Dear Lennard,
Where did you get the extra-long Eggbeater spindles shown on your ’cross bike, and how long are they versus the standard length? I’m trying to get my Q-Factors nearly identical between my ’cross and mountain bike. I’d like to add about 10mm to the standard length spindles on my ’cross bike to get them the same.
—Brent

Dear Brent,
I’ve had them for years, and I haven’t seen them promoted since. There was a time many years ago when Crank Brothers hyped the fact that it was offering longer spindles for upgrade into existing pedals, so I got some. Then when the need arose to get my stance width on my two bikes the same, I pressed them into service.

Crank Brothers does offer shorter spindles currently, so maybe you could shorten the spindles on your mountain bike instead…
― Lennard

Calling out the valve tape job

Dear Lennard,
Your previous gallery of your cyclocross mounts was brilliant, and most reassuring for fellow OCD sufferers, but, honestly, a rough swatch of insulating tape to eliminate valve “tick,” really? Why no neatly trimmed patch with an undersized hole neatly punched out, carefully applied like a collar over the valve. I’m surprised — but maybe your counseling is more intensive than mine!

Here’s a thought for Lennard Zinn’s excellent article on lab-tested seatpost damping: Very interesting stuff indeed, tending to confirm my suspicion that the best combination of setback and saddle design will probably have the saddle rails clamped at the midpoint of their length, as close as possible to the greatest available amplitude of their own deflection.
—Alistair

Dear Alistair,
That’s a good idea! My current taping method is indeed a step down from what I used to do, namely wrapping just the right number of layers around the valve extender before installing it and repeatedly trimming and testing the size until it just fit. In the end, the tape only just barely stuck up above the rim, but it took awhile to get it right. I managed to convince myself that it was insane to go to that level of compulsion to stop a tick, so I just looped tape around the valve and stuck it to the rim. I definitely did not like the look of the loop of tape and found myself re-doing it weekly, so in the end, it was ugly, and I still was anal about it. So, no, my counseling has not been intensive enough!
―Lennard

Keeping perspective

Dear Lennard,
I regularly read and enjoy your writings on the VeloNews website and in the magazine. As a tall, aspiring mechanical engineer (unfortunately in a field unrelated to bicycles) offended at the thought of paying another person to do his bicycle maintenance and repair, I thoroughly enjoy your writing on the mechanical aspects of riding. You had already persuaded me of the benefits of your tall-person geometry, but after salivating through your photo gallery, I am more convinced than before. I especially enjoyed seeing the many custom aspects of your bike: the cranks, the brake cable hanger wrapped to your fork, the derailleur pulleys, the way your cable stops are attached to your frames with rivets, and the removable dropouts. What a cool bike!

Though, I’m really writing regarding a line from your article that struck a chord with me: “I do recognize how extremely fortunate I am to be able to have such concerns and the time and opportunity to act on them, as I’m sure that cyclists in Syria, for instance, have had no such luxury for a long time now.” Although your column is not a bike advocacy column, I thought that was a completely appropriate remark acknowledging that cycling is a privilege granted to us by the stability of our world region and the bike advocates who have come before us. If nothing else, I was glad to hear that you think about the same issues that I do!

Keep sharing the knowledge, Lennard. I’ll keep reading.
—Jake

Dear Jake,
Thanks for your kind comments. It’s a good thing to remember on Christmas how blessed we are to have the secure foundation for our lives that allows us the freedom to pursue a passion like recreational cycling so wholeheartedly. I have to keep reminding myself not to exaggerate the importance of things like the details of my bikes, or even the racing itself that I have sweated the bike’s details for. As a recent example, our Colorado cyclocross season just ended with our state championships last weekend, and I blew my rear tire on the last lap just after passing the pit for the penultimate time. Getting passed by a bunch of riders before I could get my pit bike was a big disappointment for me, but it was actually the perfect thing to happen to make crystal clear to me how overly important my cyclocross results had become to me. After all, I still got to ride the whole race and benefit from the hard workout and technical challenge that drew me to the sport in the first place, plus I got some extra practice riding off-camber turns and drops on a flat tire. And in the grand scheme of things, what could really be more trivial than results in a 55+ masters cyclocross race?

We just got our first real snow of the year here, and I intend to just ride my bike in it for sheer joy and carry that spirit through nationals and worlds, no matter what happens there. I wish you all a very Merry Christmas.
―Lennard

Anchoring your workstand

Dear Lennard,
I just had a good idea whilst reading about your stand topple at a ’cross race. Drill a hole in the foot of each leg and use standard tent pegs to pin the bugger down in softer ground in the pits. On harder ground you’re screwed, but hey, I said it was a good idea not a brilliant idea…
Happy ’crossing mate.
—Mark

Dear Mark,
Good idea!
―Lennard

Breaking carbon bonds

Dear Lennard,
I had an Easton carbon road bar that has been through no crashes at all and broke where yours did JRA — I had just done a large hill and descent and was riding through town on a flat street and noticed the right drop was attached to the bike by nothing but the handlebar tape. The shop people said they’d never seen anything like it, but what broke wasn’t the tubing–it was the glue holding the drop to the straight bar. The bar was clearly made of three pieces: two drops and the straight piece between, welded/glued together, and the weld had broken. I’ve never seen anything addressing this fact about carbon bars or if it’s an inherent weakness aluminum wouldn’t have. What do you think?
—Jack

Dear Jack,
I admit I’ve often wondered about weakness at the joints of splinted carbon bars, but this is actually the first one I’ve heard of where the glue bond failed. Given that most carbon frames these days are made in a number of separate sections bonded together and those joints rarely fail anymore (as opposed to the early days of lugged carbon frames pulling apart), I’d say that the gluing technology in carbon bike parts is generally something we can be confident about, your case notwithstanding.
―Lennard

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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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