Technical FAQ: IT bands, foam rollers, and more

In this week's Technical FAQ, Lennard Zinn answers readers' questions about IT band issues, inflating tires, and more

IT band stretches

Dear Lennard,
I was wondering if you had a picture to describe the stretch you wrote about in this story.

I also have had Iliotibial band issues and would love to reduce their occurrence.

Dear Ian,
Here you go; thanks to my wife for taking the photo.

Dear Lennard,
The recent letter you received from Daniel regarding stretches to avoid pain from ITB syndrome caught my eye, having suffered the same problem. I think a foam roller is the most effective stretching method, but it must be done in conjunction with exercises to address the root cause of the problem — a strength imbalance between quads and hip flexors responsible for lateral stability.

I often have trouble if I’ve had to stop riding for more than a week due to illness or the need to travel. I think I lose strength in my hip flexors faster than in my quads during periods of inactivity. When I return to cycling, if my hip flexors are weak relative to my quads, my pedaling technique gradually worsens as I fatigue. At the start of the ride, my knees piston up and down in a fairly straight line, but as I tire, my knees gradually follow a more elliptical pattern. My ITBs are obviously working overtime to maintain lateral stability in the absence of help from my hips and they tighten up.

I’m told by my physiotherapist that the gluteus medius is the main culprit. He prescribed one-legged squats to strengthen and “activate” the muscle, which I understand to mean re-teaching the nervous system to recruit the use of that muscle more effectively. I start the exercise by holding onto the mantelpiece to keep balanced and progress to a free-standing position. I perform three sets of squats to failure using just my own body weight and try hard not to wobble from side to side on the way up and down. Another exercise I use to strengthen the gluteus medius is the “clamshell.” This is done lying on your side, heels together and raising and lowering your knee vertically. The goal of course is to get strong and develop a pedaling style like Cancellara displayed during the final 10 miles of the Tour of Flanders — that guy has some serious glute strength and endurance!

Foam rollers

Dear Lennard,
Here’s a travel-friendly foam roller for you. A bit pricier than Ben Chaddock’s PVC pipe, but not nearly as painful.

Dear Michael,
That is better than the cut-down foam roller I used to travel with. I just cut a regular three-foot roller in half, and it worked okay, but I kept getting pulled aside at the security check in Frankfurt to get it tested on some gadget in the back room (I carried it on, so I could use it between flights). I’ve had the same thing happen when I carried on a bike helmet in Frankfurt …

That Grid Mini foam roller would take up less room and allow other items to be stuffed inside it, although it’s a bit short; I’d have to change my rolling technique!

Are o-rings necessary?

Dear Lennard,
When I put on a new chain I remove the jockey wheels and clean them. The inner wheel (one closest to the cogs) of my 10-speed Ultegra derailleur has o-rings and apparently the last time I did the cleaning I didn’t get one of them seated correctly. So this time I found that it was mangled. When I asked at my LBS, the mechanic said the rings weren’t necessary and that they have on occasion simply removed them. I figure the rings must be there for a reason. What do you say?

Dear Chris,
Yes, they’re there for a reason, namely to keep grit out. But if you keep your jockey wheels clean and lubed, that’s not a big issue, and they’ll run faster without them. Or you can swap them out for a different model.

Even Wayne Stetina, Shimano R&D director, wrote to me, “I hate the seal drag of o-rings and always remove from Ultegra / XT. Retrofit DA / XTR cartridge bearing lower pulley?”

Which type of air is best for bike tires?

Dear Lennard,
I just read your recent article on VeloNews about tire inflation gases. A little background on myself, I worked for almost 10 years as an engineer with professional motorsports teams here in the United States. A few years ago there was a big stink about Ferrari’s Formula 1 team filling their tires with CO2, so I did a bit of research and experimentation into the reasons for using different gases to inflate race tires.

The prevailing opinion at the time was that nitrogen was better to use in our tires, because as the tires heated on the track, the pressure rise was less than for normal compressed air. Less change in pressure per degree temperature rise (dP/dT) means less change in tire behavior for temperature change. It became especially important to reduce dP/dT for caution periods during races and putting new sets of tires on the car — the faster you could get the tire pressure to reach your target, the faster your car got up to speed. For an example, we would set the tire pressure at, say, 21psi cold, with a goal of reaching 25psi “hot” (at roughly 200degF).

In our research, we found that the mantra of “nitrogen is better than plain compressed air” is only partially true. If you can completely dry plain compressed air, it actually has a lower dP/dT than nitrogen. Not by much, but it is better. The problem is that your typical compressor — or hand pump, in the case of bike tires — compresses the partial pressure of water in the air along with all the air. The water increases the dP/dT of the air.

As for CO2, it does have a significantly lower dP/dT than nitrogen and compressed dry air. For my example before of a goal of reaching 25psi “hot,” we could start with a cold pressure of, say, 23psi instead of 21psi. For our application, this was a big change, and a major improvement. My experiments backed up all of my theoretical results for behavior of these gases.

As a side note, in a purely theoretical sense, one of the best gases to use to reduce dP/dT in a tire would have been acetylene. However, as well as it would work, it would tend to make slow leaks a bit more … explosive.

What does this all mean for bike tires? Probably not much. I don’t see bike tires raising temperature nearly to the extent that we saw race tires spinning at 235mph. I’d be more worried about the temperature of the gases you’re putting in the tire initially — if you’re filling a tire from a compressed tank, there will be some expansion cooling happening to the gas as it enters the tire, which will cause the pressure to rise as it warms up to roughly ambient in the tire (think of how cold CO2 cartridges get when you release a lot of gas from them). I use whatever is most convenient!

Dear Enzo,
Amazing coincidence that you worked in motorsports and have that name!

I saw nitrogen used as an inflation gas at the Sebring car racetrack to keep the humidity in the tires lower.

We had a discussion four years ago about how CO2 bleeds out of bike tires faster than air. I wonder if that happens in car tires? It seems hard to imagine that Enzo Ferrari would use it if it did.

Since we got a foot of snow here in Boulder every week in April and the first week in May as well, I might as well publish some feedback on the story about cycling in cold weather I wrote in March, when I thought we were about done with cold weather.

Flawed science?

Dear Lennard,
I have always enjoyed your articles, particularly the emphasis on separating science from marketing and fiction.

Unfortunately, your article titled “Technical FAQ: Why is riding in the cold so hard?” misses the mark, and provides physically incorrect results and analysis from your “experts.”

The main point of concern comes from Chet Wisner stating that, “drag increases by the square of the speed. The ratio of the squares of 21 mph and 20 mph is about 1.10. So, this increase would have the same effect on the drag you are pedaling to overcome as the 50-degree Fahrenheit temperature difference.”

This is a flawed statement. While yes, the drag varies as the square of the speed, it is not correct to compute the velocity by equating the drag.
The power to propel the cyclist is what should be compared. That is, how will the velocity vary between two days if the power is maintained constant?

Since Power = Velocity x Drag, the power increases with the cube of the velocity. As stated in the problem, assume a cold to hot density ratio of 1.10. A rider putting out the same power would not increase their speed by 1.1^(1/2), but instead, by 1.1^(1/3). That is, the importance is exaggerated with Chet Wisner’s approach. Using his approach, 20 mph on a cold day equates to 20.98 mph on a hot day with a 10% decrease in density. However, the actual value computed will result in a speed increase to 20.65 mph (see page 4 of attached calculations).

Len Brownlie (who you quoted earlier in the article) understands this point, noting that you can compute how much longer it will take for “the same cyclist, generating the same power,” to complete a 40km course on a cold day.

Unfortunately, his actual calculations are wrong. Any undergraduate engineering student who has taken a fluid mechanics course can quickly work through the calculations for the prescribed density variations (see attached pages 1-3). Assuming on a hot day a rider does 40 km in 58:37, with the values given in the article, the average power can be computed to be 199.65 watts. Now, repeating the calculation for the cold day, solving for the average speed at the given power, and then determining the time to complete 40 km at the computed average speed reveals a final time of 60:45, not 60:00. I’m sure you’ll agree that 45 seconds over a 40 km distance is pretty significant.

Even his computation of “performance decline” is incorrect. Using his own wrong numbers, the percent decline in performance (based on time) is 2.36 percent, not the stated 2.77 percent. The actual performance decline, using the time difference between 58:37 and 60:45 is 3.64 percent.

In summary, I applaud you for your efforts to bring the scientific side to cycling, but I implore you to be more careful in your use of “experts,” or incorporate better editing to avoid simple mistakes such as these. The only thing worse than justifying performance decisions based on anecdotal evidence is to base them on misleading and inaccurate scientific decisions.
—Byron D. Erath, Ph.D.
Assistant Professor
Clarkson University Department of Mechanical & Aeronautical Engineering

Dear Lennard,
In your VeloNews article from March 12, you quote two readers that indicate an increase in air density of 10 percent is equivalent to an increase in speed of 5 percent. This is correct for the force but it is not for the rider’s heart. What the rider feels is the required power. The power is proportional to the force multiplied by the speed with respect to the road, thus the air drag power required is proportional to the relative air speed cube. An increase in air density of 10 percent at 20 miles an hour in a no wind situation is equivalent to an increase in speed of 3.333 percent (10/3) or 20.7 miles an hour.

It is also equivalent to riding at 20 miles an hour in a 1 mph head wind.

P.S. Your technical articles are gems.