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Technical FAQ with Lennard Zinn: Tires for cyclocross

  • By Lennard Zinn
  • Published Jan. 15, 2013
Challenge and FMB suggest that diluting Aquaseal (Aquasure in Europe), but Dugast points out that Aquasure does not contain toluene, which is barred in Europe. Photo: Lennard Zinn | VeloNews.com

Editor’s note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

Dear Lennard,

I read the whole photo article on your bike, and I really enjoyed it. You asked for replies if you wanted more “geek-out” on cyclocross tires and wheels. Please put me down for one vote “yes.”

—Chris

Dear Chris,

I’ll answer this question generally here for tires only. And, as the cyclocross national championships are fresh in my mind and cyclocross world championships are coming soon, I’ll follow this up in subsequent days with more detailed specific tire information from that perspective. Next week I’ll talk about wheels.

Tire choice

When it comes to tire choice, there are three basic tread choices in tubulars: mud, file and mixed condition. Width since inception of the UCI 33mm-restriction is usually 33mm and sometimes 32mm. A larger tire floats better and has more surface area for traction, whereas a narrower tire is lighter and can dig down for traction in soft conditions.

Popular mud treads are Challenge Limus, Clement PDX, Dugast Rhino and FMB Gripo XL and Super Mud. A good mud tread has tall, widely separated knobs with angular edges to shed mud and provide grip. The knobs can be big and sharp because the soft conditions don’t tend to wear them down rapidly or tear the knobs off when cornering.

File treads you commonly see in domestic racing are Clement LAS, Vittoria Cross Evo XN, Challenge Grifo XS, FMB Sprint, Dugast Pipistrello and Pipisquallo, and Tufo Dry Plus.

Also called “diamond” tread, these have small diamond-shaped bumps down the broad central tread strip and usually side knobs as well. The Pipistrellos have almost nonexistent side knobs, while the Pipisquallos have Rhino-like side knobs. Challenge promises to have a Limus XS soon, which will have larger side knobs than the tiny ones on the Grifo XS.

File-tread tires tend to be great in sand (since they don’t churn down through the crust as much and keep the rider a bit more on top of the sand). They are also good on grass; hard, fast courses; tacky “peanut butter” surfaces; and ice (more contact area). They tend to be the lightest tires, since they have few knobs and thus less rubber.

Mixed-condition tires generally have central chevrons and linear arrows bounded along the edges by round and semicircular side knobs. Popular versions are Dugast Typhoon, Challenge Grifo, Vittoria Cross Evo XG, Tufo Prestige or Flexus Primus, and FMB Grifo or SSC.

Obviously, if you only have one set of tires, this is the type to get. The knobs on mixed-condition tires tend to be tall enough to offer reasonable mud traction and are separated enough that they shed some mud. With the central arrows, they roll reasonably fast, and they have good edge grip.

Typhoons save weight at the expense of some cornering traction by having one less row of side knobs than Grifos. The Fango tread from Challenge and FMB is also a very good mixed-condition tread. Despite the fact that “fango” means “mud” in Italian (“limus” means “mud” in Latin, by the way), the knobs are neither tall enough nor separated enough to be really good mud tires. But they have great cornering edges, roll very fast on hardpack and grass, don’t dig badly into sand, and offer quite good snow traction.

Pressure

Tire pressure depends upon rider and course. The more traction required, the lower the pressure. The more pinch-flat and rim protection from sharp edges required, the higher the pressure. The lighter the rider, the lower the pressure, and vice versa. The less a rider can deal with a squirmy tire, particularly on pavement, the higher the pressure.

It takes a while to get used to riding tires that are close to flat. As an example, road riders might be surprised to know that 35psi is very high, and 30psi is definitely on the high side, for tubulars in cyclocross. In super-slick conditions, top riders often run close to half that pressure — 17-18psi. Given that ambient air pressure at sea level is 14psi, you can see that this is almost flat.

Obviously, you cannot hit hard edges fast with pressures this low and expect to not get a flat or a damaged rim, but when the course is super slippery and is either soft or the speeds are very low, this kind of pressure can make the difference.

Gluing

The tires must be glued on well, because they are running at low pressures and are so large that they don’t fit the top profile of a road rim very well. Both of those things mean that they will not adhere as well as a road tire with the same methodology and gluing will need extra attention. I’ve discussed this issue a lot here.

Sidewall protection

Tubulars with cotton casings can be compromised by all of the abrasion and washing from a muddy race. The cotton can be abraded and can rot. High-end tires have very thin casing threads, so only a small amount of abrasion resulting in fuzzy sidewalls can mean that the threads have lost much of their strength. And obviously, rotten cotton is not strong.

What to do? After they’re glued on, so you can seal the edge of the base tape right down to the rim, coat them with a waterproof protectant. Tubular tires generally have an unvulcanized latex coating on the sidewalls, which can be rapidly removed in cyclocross. And superlight tires will of course have less latex on them so that they’ll tip the scales less, which sells more tires.

The standard method is to coat them with McNett Aquaseal urethane repair compound. This stuff is waterproof and protects well, but it adds considerable weight and stiffens the casing, making the tire less supple. It is also very thick and hard to apply and get smooth. In the next installment, I’ll describe how to apply it.

Another option is McNett Tent Sure tent-floor sealant. It’s waterproof and thin and very easy to apply with the supplied foam brush. On the other hand, it doesn’t last long. Same goes for liquid latex.

FILED UNDER: Bikes and Tech / Cyclocross / News / Technical FAQ TAGS: / /

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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