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Technical FAQ: Sealing, gluing, and inflating cyclocross tires

  • By Lennard Zinn
  • Published Sep. 24, 2013
Autumn is back and with it, a range of cyclocross tech questions. Photo: Caley Fretz | VeloNews.com

There is a nip in the air this week and cyclocross season is fully underway. We’ve received a number of ’cross-related questions lately, from tips on sealing and gluing tires to the proper air pressure for clydesdales.

Why aero wheels for cyclocross?

Dear Lennard,
Why are aerodynamic carbon wheels prevalent in ’cross? Doesn’t seem like much advantage in a one-hour race at ’cross speeds, plus they tend to be heavier and therefore harder to accelerate out of turns.
—Jim

Dear Jim,
What you say is true about weight and acceleration. And the tall profile makes them vertically more rigid, when a bit of shock absorption would be nice.

However, in mud and sand, they offer advantages. Their tall profile minimizes the amount of mud they can carry, and it also gives them improved tracking in deep sand and mud.

And, for really fast guys, aerodynamics will make some difference, as riders tend to be riding alone rather than in a paceline in ’cross.
―Lennard

Advice on diluting Aquaseal

Dear Lennard,
I’ve been thinning out Aquaseal with Toluene (the solvent in Aquaseal) and painting it on with an acid brush to seal tubulars. I thin it out to the consistency of maple syrup. You can apply a thinner layer and it allows you to seal around the base tape very effectively.

A strip of electrical tape applied on the rim first (I do this before gluing and leave it on until the tires are sealed) allows you to be a little more liberal with the application. Any Aquaseal that overlaps onto the tread will come off in a ride or two.

I’ve been using this method for years and haven’t found any issues with the added solvent compromising the integrity of the tire or base tape.

I recommend good ventilation for this method!
—Chris

Dear Chris,
That sounds like a method worth trying. Aquaseal is gloppy stuff and not easy to get smooth.

My biggest concern would be about the toluene dissolving the glue holding on the base tape or even the rim cement. But you say you have no problems with that, and it seems as though you’re only getting it on the edge of the base tape, and it evaporates quickly, so that concern may be minimal.
―Lennard

Ever Dry for tire waterproofing

Dear Lennard,
Regarding your recent article about Aquaseal for ’cross tires, what are your thoughts on this nanotech substance as a tire sealant?

Looks like it does some pretty amazing things for construction, think it could be just as incredible for —cross?
—Sean

Dear Sean,
I have not tried it. If you do, let me know how it works.
―Lennard

How much stretching is too much stretching?

Dear Lennard,
I recently read your article on gluing cyclocross tubulars, and I was hoping you wouldn’t mind a question about one aspect of the process. You recommend Pete Webber’s tip that once the glue on the tire has set up to then stretch the tire onto a clean temporary rim. I tried this with my last wheelset, and it absolutely accomplished the purpose of making the final installation easier!

Everything about the first wheel went perfectly. However, when I went to remove the second tire from the temp rim, it was a little difficult, and strips of glue got pulled off of the base tape and remained on the temp rim. In essence, the tire had started to bond to the temp rim. I put some additional glue down to patch up the now bare spots on the base tape and proceeded, but I certainly preferred the outcome of the first tire.

Could you provide more details about the step of stretching the tire onto a temporary rim? Do you think I installed the second tire onto the temp rim before the glue had fully dried? Both tires had dried overnight (approximately 10 hours) and both tires remained on the temp rim for about 12 hours before removing them to mount on the wheels. Did I leave them stretched for too long? Or perhaps my glue job on the second tire was just splotchier and less uniform, causing the chunkier spots to bond to the temp rim?
—Oscar

Dear Oscar,
You left the tire on too long, and your clean rim is no longer clean enough. I just put the glued tire on the unglued rim for a few minutes, right before installing it on the glued rim.

Just mount it on the unglued rim, pump it up, deflate it, pull it off of the unglued rim, and put it on the freshly glued rim. That accomplishes 90 percent of the stretching you achieve by leaving it overnight, with much less likelihood of it getting bonded to the rim.
―Lennard

How low can I go?

Dear Lennard,
In one of your columns on cyclocross you say tire pressure is often close to 20psi and should be less than 30psi. I am 195 pounds an often run 35psi and still feel like I could bottom out on my FMB SSC. What is your recommendation about psi and rider weight?
—Doug

Dear Doug,
My only firm recommendation is that the heavier you are, the more pressure you should put in your tires. But how much you are comfortable with is very individual.

A few years ago, 26psi was simply too low for me to ride; I felt like I had too little control of where the wheel was going. And yes, I certainly bottomed out plenty. I weigh 172 pounds.

Now, I am quite comfortable at 26psi and with bottoming out a lot. The latex tubes in good tubulars can take a fair amount of bottoming out without pinch flatting. I still can’t imagine the sub-20psi pressures some guys who are faster than me can ride.

My guess is that you can get down to maybe 31psi on the front and 33psi on the rear without damaging your tires. It will take some practice to become comfortable with that.
―Lennard

Why all the mechanicals in Louisville?

Dear Lennard,
I was sort of stunned by the number of mechanicals that happened in Louisville at the world championships. Katerina Nash lost a podium spot to a dropped chain when she shifted to the big ring in the finishing straight, Jonathan Page dropped out of the top 15 with multiple mechanicals and others had race-ending mechanical mishaps. I can’t imagine a more important event for things to go well and I’m sure mechanics were spot on with bike prep and in-race cleaning. So what gives? Is it pilot error during shifting (not likely given the level of expertise), not pitting enough, too much mud accumulating on one bike versus another, or just superior equipment on some bikes (haha)? I don’t recall hearing the Belgians or Dutch racers having such bad luck. What gives?
—Glenn

Dear Glenn,
Actually, Kevin Pauwels (a very fast Belgian and one of the pre-race favorites) had plenty of problems with his front derailleur in that race, so it was not limited to the Americans (or U.S.-based Czechs).

First of all, shit happens in muddy, sloppy races in the cold, especially when a championship is on the line and riders are going harder, as well as taking more risks, than they normally would.

In general, most mechanicals I am aware of at worlds were with the front derailleur. That’s generally the most problematic part of a ’cross bike.

There are a couple of things that I can say about it. One, and I’m pretty sure this applies to Pauwels, is that electronic shifting systems encourage riders to use their front derailleurs more than they normally would, because it’s so easy to shift. But even they can screw up if the rider shifts under too much load at low speed or gets a stick caught in there.

A single front chainring would eliminate a lot of the mechanicals you saw. You can do it with Di2, but, though few use Campagnolo EPS in ’cross, you can’t run a single front chainring on Campy EPS-equipped ’cross bike, because the system keeps going to sleep if the front derailleur is not connected. In other words, as long as you’re shifting constantly, it continues to work, but once you don’t shift for a while, you repeatedly have to hit shift buttons before anything happens.
―Lennard

Did I damage my rims peeling the tires?

Dear Lennard,
I recently bought a used set of carbon tubulars, with tires mounted. To be sure of the glue job underneath the tire, I am removing the tire and re-gluing them; the tires lifted off the rim fairly easily but it looks like it took a layer of the rim off in a few spots. There’s some carbon stuck to the base tape of the tire. The biggest spot is about two inches long and the width of the base tape, with a few other smaller spots around the base tape. I assume that I will need to glue new tires on, but is this a problem for the rim?
—Ryan

Dear Ryan,
Pulling off of some fibers in the top layer of carbon on the rim bed happens sometimes during tire removal, and it’s impossible to judge at this distance how much your rim is compromised. I have often gone ahead and glued another tire on in this instance, and I’ve never had a carbon tubular rim failure. However, if yours is a big or multi-layer patch of missing carbon, it should be repaired by a good carbon repair place (we’re lucky that there are a lot of them now).
―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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