Technical FAQ: Road discs with Campy, high-speed shimmy, and more

Lennard Zinn discusses hydraulic disc brakes with Campy levers, problems with shimmy, and more in this week’s Technical FAQ

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Road disc brake options with Campy

Dear Lennard,
At long last, I took the plunge and built up an old frame with a new 10-speed Campagnolo Veloce group. I love it. But it’s caused a conundrum. I’ve been planning to build up a steel disk specific cyclocross frame (as yet unspecified.) Twenty years of bad weather commuting and 20 years on mountain bikes with equipment ranging from [cantilever brakes] to hydraulic discs tells me discs are the way to go. But all the cable-actuated options seem to be specific to Shimano/SRAM levers.

Do you have any recommendations for disc brakes and Campy levers?
— Ed

Dear Ed,
The Campy levers have virtually the same cable pull and leverage as SRAM levers. I personally have used Campy levers with TRP HyRd and TRP Parabox cable/hydraulic disc brakes, along with Avid BB7 and Hayes CX Pro cable disc brakes. They worked fine with all of them, although I would have preferred more cable pull with the HyRd brakes.

I’m guessing that the HyRd brakes would work better with Shimano levers because of their greater cable pull. The HyRd system requires a long cable pull in order to keep it as an open system; if you have the cable pulled up short enough to have early engagement when you pull the lever, then the piston will not retract beyond the metering hole. If this happens, then it is a closed system, since brake fluid cannot flow back into the reservoir from the hose, meaning that it is not self-centering. So, like a cable disc brake, as the pads wear, you would still have to keep tightening the cable, whereas one of the beauties of hydraulic disc brakes is that as the pads wear, the pistons move outward more so that the space between disc and pad stays constant.
― Lennard

Help With Shimmy

Dear Lennard,
I ride a Trek 1500 road bike, and recently I noticed that whenever I take my hands off of my handlebars, my handlebars and front wheel vibrate/shake extensively.

Any suggestions on what the problem is and what I can do to fix it would be greatly appreciated!
— Mike

Dear Mike,
Here is the answer to why it happens.

You can keep following the links back in each article on shimmy to more articles I have done on it, describing fixes and riding techniques to deal with it. Note that resonance, which is often used to describe bicycle shimmy, would only occur at a very narrow speed range. I don’t know of anybody who, when their bike started shaking, sped up in order to see if the shaking would stop (which, if it did not, would definitively rule out resonance), but simply the fact that the shimmy builds as the speed builds is probably proof enough that it’s a Hopf bifurcation, as opposed to hitting the resonant frequency of the bike/rider combination. In both instances, though, increasing the weight of the rider or decreasing the stiffness of the bike will increase the shimmy problem.

As you can see, the first thing to try is stiffer wheels, and make sure that there is no hub-bearing end play. Adjusting a too-tight or too-loose headset can be a cheap fix. A misaligned fork can also do it. If those fixes don’t solve it, a stiffer frame is required.
― Lennard

Dear Lennard,
Thank you for such a well-explained reply to my shimmy problem. Yes, my headset was loose, but the hubs were tight.

I did a lot of research on Google, and found that many suggest leaning into the front wheel, rather than moving their weight onto the rear.

But what I found most interesting was an article that you wrote many years ago, in which you suggested going into a quick right turn. This, along with your e-mail, led me to my revelation: riding a bike downhill is very much like skiing downhill. But consider the skis one can choose: slalom skis are short, light and quick; giant slalom skis are longer, heavier and not as quick; and of course downhill skis are even longer, and are much heavier, and are built to descend at high speeds without vibration.

So, as you described my bike, I thought of slalom skis. And just as slalom skis vibrate at high speeds when going straight downhill, I went up to Galena Summit on a very windy day and descended, but I applied my skiing theory by linking together a series of descending turns. Honestly, I felt like I was cruising down warm springs on my moguls skis — rhythmically linking one turn after the other, all at high speed and without a single wobble.

I have never had so much fun descending and I have never felt so safe.

Thank you for your inspiration.
— Craig

Dear Craig,
And just like in skiing, you can use that method to slow down when braking is problematic for any number of reasons (like incompatibility of the rim and brake pads, or a bumpy braking surface, or the bike is shaking too much).
― Lennard

More on chamois rashes

Dear Lennard,
I followed with great interest the commentary on groin rashes, allergies, etc. last year. I have suffered for over a year with pain akin to sitting on razor blades. Assuming it was related to friction, heat, moisture, and the like, I tried every lubricant known to man, including K-Y jelly recommended by a female rider. Nothing seemed to work so I treated the pain as if it was an actual rash. I tried over the counter remedies and eventually a couple of different prescriptions from my doctor. Though there was some relief, the pain would always return with a vengeance.

I ran across this article last month and immediately stopped using baby wipes and body wash. Within a couple of days the pain was subsiding and I’m happy to say the pain is completely gone.

After hundreds of dollars in remedies, it appears the culprit has been the chemical in the wipes and body wash!
— Scott

Dear Scott,
Wow! That’s insidious! The fact that liquid hand and body soap is everywhere now makes this ever more interesting.
― Lennard

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