Technical FAQ: high-speed shimmy, tubular tires, accuracy in tire pressure

Have a question for Lennard? Please email him at veloqna@comcast.net to be included in Technical FAQ.

Dear Lennard,
One other question I’ve been meaning to ask is about your current thinking on the dreaded shimmy. Knowing now that it’s a bifurcation and not an oscillation, I’m wondering how much is equipment, and how much is rider input? I think I mentioned that the shimmy happened a few months ago to a friend on a modern road bike (a newish Trek Domane). He is a less experienced rider and was in a nasty crosswind. Are there strategies he can use to avoid a repeat performance? I’ve been advising him to put all his weight on the pedals, floating off the seat, with loose hands on the bars, but mostly because that’s what I do, and I’ve never experienced any shimmy in 50+ years.
— Steve

Dear Steve,
The occurrence of a shimmy requires a connection between the wheels, just like a phone made of two tin cans connected with a taut string. If you can completely de-weight one wheel, the oscillation will go away, just like you can’t place a call on the tin can phone if the string is slack.

Peter Sagan could probably break the connection between the wheels in almost any situation by pulling a wheelie; heck, he could probably also do a nose wheelie at any time. Either would eliminate shimmy, but few people can do that.

Pushing the butt off of the back of the saddle to get the weight as far back as possible and having no weight on the front wheel should stop it. It takes a big leap of faith to pull that off at high speed on a violently shaking bike, though.

Just clamping your knees against the top tube damps a lot of the oscillation and does not require such a leap of faith.
― Lennard

Dear Lennard,
I seem to recall that you are somewhat of an authority on tubular tires. Do tubulars of a given width come up rounder/wider on a rim (of given width) than their clincher equivalent?

I recently listened to a podcast featuring an interview with a senior rep from Challenge tires, who spoke about their emerging tech including tubeless tubulars, and some new tubular tape (I currently use Carogna, but surely some competition would be no bad thing). Do you have any insight on this?
— Steven

Dear Steven,
In answer to your first question, the answer is most definitively yes; a tubular tire is completely round in cross-section, while a clincher is bulb-shaped.

The Challenge tubeless tubular was discovered by accident, when the latex tube had not cured completely before being put inside of the casing, and it stuck to the casing. Now, Challenge does that intentionally and permanently adheres the tube to the inner walls of the casing. My guess is that it makes for a very fast-rolling tire that is protected against punctures by sealant and against pinch flats not only by the lack of a tube, as tubeless clinchers are, but also by a flatter rim that doesn’t extend up the sidewalls with a thin top edge to either pinch the tire or to be bent or cracked by a hard, sharp-edged impact. I intend to test this hypothesis soon.

As for Challenge’s new tubular-gluing tape, I recently got some. It looks just like 3M VHB tape, probably 5952 3M tape, but perhaps 5962 3M tape (thicker, denoted by larger last two digits). I haven’t tried it for gluing tires. We use 3M 5952 to glue on your 40th Anniversary of Zinn Cycles head badges, and it is fantastic for that; it’s very hard to remove the head badge if you put it in the wrong place or upside down. I don’t know if it can outdo Carogna for holding tubulars onto rims.
― Lennard

Dear Lennard,
In reply to a query from Kimball about a larger valve standard for tubeless, you mention in your reply that you “can’t imagine the bike industry going through the massive upheaval it would take to switch to a different standard”.

When I think of the endless proliferation of bottom bracket standards, disc brakes, wider rims and tires, and all the rest, I can imagine the industry making such a move. If there’s money to be made. Presently, in the bike industry, early obsolescence of perfectly usable equipment seems to be the new standard. As an example, trying to obtain parts for “legacy” (ie, 3-4 yrs. old) Zipp wheels or Powertap power meters is a chancy proposition. The Powertap has been discontinued as are some not-very-old Zipp models, so good luck with that. As you know, both are now in the SRAM stable, along with Time pedals, too. As a Time user since 1990, I’m starting to collect cleats, because with SRAM, who knows how long I’ll be able to ride these two-year-old pedals in the future?
— Pierre

Dear Pierre,
Point taken. I’ll keep an eye out for new tire valves.
― Lennard

Dear Lennard,
I was always wondering why my floor pump gauge starts at 0 Bar.

As we all know, we don’t live in a vacuum. I’m mostly at sea level so it should read 1 Bar to start with. So, I guess it is some sort of convention between various manufacturers, that gauges at pumps start at 0.

What I was in fact wondering is, if my tire says max pressure 8 Bar and my pump starts at zero, how much pressure do I really have inside my tire by the time I reach 8 Bar? If the start on the gauge is zero, and I know for a fact I am at 1 Bar atmospheric pressure, by the time gauge reads 1 Bar, I am already at 2 inside the tire. So, by the time I reach 8 Bar on the gauge, the tire is actually at 9 Bar exceeding the max pressure allowed. Or, I’m missing something?

Maybe you can clarify in few words what’s this all about?
— Sead

Dear Sead,
The pump reads zero whenever the pressure inside the hose equals the pressure outside of the hose. So that means it reads zero when it is not pumping, whether you are down at 282 feet below sea level in Death Valley (ambient pressure = 1.03 bar), or when you are at the top of Mt. Everest (ambient pressure = 0.337 bar).

When the pump shows 1 bar, it means that the pressure it is reading in the tire is 1 bar (14.5psi) higher than the ambient pressure, not that its absolute pressure is 1 bar.
― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), 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.

Follow @lennardzinn on Twitter.