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Technical FAQ with Lennard Zinn: Keeping cyclocross brakes centered, pulling that PT crank

By Lennard Zinn • Published

Q. Dear Lennard,
I recently purchased some Avid Shorty Ultimates for my ‘cross bike. I brought my bike in to my local shop to have a “professional” install them.

Avid's Shorty Ultimate
Avid's Shorty Ultimate

The mechanic set them up with the wide stance in the front and narrow in the rear, which is fine with me. I rode the bike around the block, and saw that if I ever did a sharp turn with the front wheel, or held the handlebar at a sharp angle, say when doing a run-up, the straddle for the front brake cable shifts slightly to one side, and then the non-drive-side brake would practically be rubbing against the rim.

The problem could not be corrected unless you manually centered the straddle again. I went back to shop and was told this was a design issue due to the self-centering floating straddle. Doesn’t seem like many of the CX pros in the world would be using this brake if this was indeed a “design” problem. Can you offer any advice on how to fix this?
— Ryan

A. Dear Ryan,
This is what Chris Shotwell, the ‘cross brake wizard and avid (pun intended) masters ‘cross racer from the SRAM tech center in Colorado Springs has to say:

“First off, I would pitch all the housing and zip-tied bits and pieces attached to the straddle wire and yoke to remove all interference with the yoke or its ability to center itself. My assumption is that the spring tension is not balanced or there is an ever-so-slight difference in the caliper’s ability to pivot on the boss.

So what I would do is:
1) Get rid of all the junk on the straddle wire;
2) disconnect the brake as if the front wheel were going to be removed;
3) using a 4mm Allen key, remove both brakes from the posts;
4) pull the springs off each assembly and note the difference between the Right and Left so they go back on correctly ( there’s a red mark on the end of the left spring );
5) re-install the caliper without the spring and tighten the bolt on the spring cap;
6) both arms should rotate on the boss without any drag or interference. If not, then start looking for where the drag is coming from. Paint on the boss? Is the brake rubbing on the spring cap? Is the boss deformed in some way that’s preventing a decent range of motion? (Perhaps tight, then loose);
7) Once the source of drag is removed, re-install the brakes with the springs in the assembly and make sure that both springs are preloaded evenly.

That should do it.”

I use those brakes myself on one of my ’cross bikes and have never experienced that problem. That said, when I changed the fork on the bike, both brake arms bound up due to the shorter length (by under a millimeter) of the bosses on the second fork. I had to file some length off of the center sleeve of both brake calipers until they both rotated without drag. I checked them with no spring on there, the way Chris suggested.
— Lennard

RE: Dear Readers,
I promised some time ago that I would let you know when I found a good solution to removing the new Campy PT cranks. Here is one sent in by a reader:

“After months of getting the run around and BS from Campy, here’s my real world blue collar, tried-and-proven solution to remove a 2011 PT left crankarm. It’s simple, inexpensive and works for aluminum and carbon crankarms.

The puller is just 24 bucks
The puller is just 24 bucks

Extractor: T & E Tools one-ton two-jaw puller model J1020 available for $24 on Amazon via Apex Tool Co. This small simple tool seems like it was specifically designed to remove PT crankarms. It’s easily available in the U.S., self centering, has self grasping, chisel point heads to fit in the narrow area behind the crankarm and is small enough to fit in my standard bike tool box. Plus it does not mar carbon arms and can be modified/extended to pull the PT right crankarm bearing down the road.

Plug: Using small socket with lip that fits securely into the PT fixing bolt (you could also use a strong washer or everyday socket extender). Campy sells an über expensive plug but it’s not needed — unless you have Campy fetish.

1) Back out the fixing bolt a few turns to give the crankarm room to move;
2) slide socket into the fixing bolt;
3) install and snug up the extractor making sure it is straight and aligned;
4) tighten extractor screw with adjustable wrench till crankarm moves out close to fixing bolt;
5) remove extractor, socket, fixing bolt and then pull crankarm fully off.”

— John

Q. Dear Lennard,
I have a Madone 5 series with an all Ultegra group. Intermittently, when I coast then start pedaling again there is a loud click or snap. It sounds like the chain is coming off a gear and then snaps back into place. The sound refuses to be recreated in the shop on a trainer.

It always happens when in the large chainring and any one of the five larger rear cogs. I have replaced the chainring, the chain, and the cassette. It still happens. It doesn’t appear to be harming anything that I can see and the chain never comes off. When I describe this to the mechanic at the local bike shop, he looks at me like I have three heads. Any ideas?
— Steve

A. Dear Steve,
I’m pretty sure it’s inside the freehub body. One of the pawls is sticking, broken, or somehow compromised, or the body is flexing so that one pawl misses its first grab.
Try another wheel and see if it goes away.
— Lennard

RE: Dear Lennard,
You were exactly right. The pawls were dirty and sticking and I had a frozen bearing in the freehub. The shop installed a new freehub and I am riding again, noise free.
Thanks very much!
— Steve

Q. Dear Lennard,
I recently purchased a new set of tubular road wheels, the boydcycling.com 38mm. Boyd says run a 21mm width tire; I was gonna use the Vittoria Corsa Evo CX. The 21 mm seems very skinny; how will this compare to the 23 I usually use? 23s are more comfortable, more meat to keep my neck in place. I use the Continental 22/24 combo the Attack/Force setup; what about using a 21 in the front, and a 23 in the back?
— Craig

Q. Dear Craig,
With my size, you couldn’t pay me enough to ride a 21mm tire. Well, maybe you could, but I would whine about it and get it off of my bike as soon as I was no longer being paid to ride it.

The weight and aerodynamic savings would not be worth the loss of the comfort, cornering grip, lower rolling resistance, and reduced propensity for pinch flats and rim damage of a 23mm tire to me.

I contacted Boyd Johnson about why he recommended this to you, and he replied that, “On the 38mm tubular set that a customer purchased, I recommended the 21mm Vittoria Corsa EVO CX tubular tires. They are one of the nicer tires out there and I have used them for many years in my own racing. Recently a lot of interest has been given to the “wider is better” for carbon wheels.

A few of the manufacturers have gone to different shaped rims while some remain with the older style shape and width. All claim that their design is the fastest and have data to prove it.

For my small company, we can’t afford to produce thousands of sample shapes in the hopes of finding one that will be 5-10 seconds faster over the course of an hour. We are still using a 20mm wide rim for which the 21mm wide tire fits great. One of the most important things for aerodynamics of a wheel is how the tire interacts with the rim itself. With these new wide rims, a wider tire works much better in having the air transition from the tire and over the rim. With the traditional “narrow” tubular rims, a 21mm wide tire matches the profile a lot better than a wider 23mm tire.

While aerodynamics are important, there are other factors to consider. This customer wanted a 38mm tubular wheelset, a very lightweight set that is great for hilly races (it’s also an extremely strong set as 2007 criterium national champion Shawn Milne has been racing them for cyclocross this fall). With the weight consideration in mind, we were able to save over 30 grams of rotational weight by using the 21mm wide tires. This is going to make for a wheelset that better suits the needs of what this customer was looking for.
— Boyd

Now you have all of the pros and cons laid out and can choose for yourself. But if you’re not swayed by the rotating-weight argument but are concerned about aerodynamics, it will only matter on the front, so you could feel that you’re getting the best of both worlds by doing the 21mm on the front and the 23mm on the rear.
— Lennard

Follow Lennard on Twitter at www.twitter.com/lennardzinn

Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, 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.” 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.

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