Tire choices for ‘cross: Lennard Zinn revisits a demanding U.S. national championship

Tire choices changed as rapidly as the weather during the USA Cycling Cyclocross National Championships in Wisconsin. But by the time the elites took the course on Sunday, the selection was pretty straightforward, with pressure being the critical factor.

The tire types are all described in my previous article from nationals. Meanwhile, scroll down in this article for clarification of an error I made previously regarding pressure.

Elite women

Saturday night in Madison was very cold, and Sunday dawned at around 15 degrees Fahrenheit. The men’s collegiate races faced dry, rock-solid conditions. There were frozen ruts everywhere, although a USA Cycling official said organizers had knocked them down substantially using a Bobcat, whose operator spent the night driving the course in reverse, dragging its blade.

It was obvious in walking the course that this work had greatly smoothed many sections, particularly the switchbacks around the pit and on the last three climbs (above the library, just before returning to the finish straight). Ruts remained, and the grading had produced a lot of hard rubble, but the depth of the ruts (and, in my opinion, the danger they posed) was greatly reduced.

However, riders did not tend to walk the course, and it was not so obvious to those who hit this hard surface how much less rutted it was, since they were still being bounced around hard. And the sections around the soccer field and behind the food tent past the second pit did not look graded at all to me.

“I could wash one wheel of my car and say I washed my car, too,” said Ryan Trebon.

For the collegiate men, everything was solid save a single mud puddle on the westbound leg around the soccer field, where I saw a rider crash trying to avoid the puddle. He was thrown down hard when the ruts grabbed his tires as he tried to change direction.

The collegiate men could have used file treads as well as anything else, running sufficient pressure to avoid pinch flats.

Many elite women started their warm-ups on file or mixed treads, but the sun came out and turned the track into sticky mud despite air temperatures in the low 20s, and they pulled in after a lap dragging bikes laden with mud.

Most of the top women raced on mud tread and were pitting every half lap, as their bikes would pick up perhaps 30 pounds of mud. The ground had become soft enough on much of the course that pinch flatting was not the overwhelming concern it had been for the collegiate men.

Winner Katie Compton (Trek Cyclocross Collective) rode FMB Super Mud tires at 20.8 psi front and rear. She used three different bikes, and some of the FMB Super Muds she rode had the PRO casing sidewalls (coated with pink latex), “which don’t fold as much as the standard cotton,” according to her husband, Mark Legg-Compton.

“We had one white Super Mud, which is a little softer rubber; she wore out the rear tire,” he said.

Diminutive Kaitlinn Antonneau (Cannondale-Cyclocrossworld.com) rode Dugast Rhinos at 18 psi in the front and 19 psi in the rear.

Elite men

Temperatures stayed in the 20s for the men’s race, but the far northern sun disappeared early in the race, making mud buildup on the bikes a decreasing problem as the race wore on. Mud tires were still the order of the day, but most riders were favoring higher pressures.

“You wanted the low pressure for traction, but you needed higher pressure for protection [from the ruts],” said bronze medalist Jamey Driscoll (Cannondale-Cyclocrossworld.com).

The maximum 33mm section also seemed to be the standard. Driscoll rode Dugast Rhinos at 26 psi front and rear.

Winner Jonathan Page (ENGVT) said he raced Challenge Limus tires.

“But I am not sure what the pressure was as I ended up adding a bit and then taking some away at the start,” he said.

Cannondale-Cyclocrossworld.com’s Tim Johnson was on Rhinos at 25 psi front and 26 psi rear, and teammate Ryan Trebon used Clement PDX at 27 psi front/28 psi rear.

Silver medalist Zach McDonald (Rapha-Focus) was among those riding the lowest pressure, using Dugast Rhinos at 20 psi, while his teammate Jeremy Powers used the same tires at 23 psi.

Each Rapha-Focus mechanic uses a different gauge system and uses it exclusively on riders in his care, since discrepancies between gauges can be meaningful at low pressures. This ensures that a request for a half-pound difference, for example, will result in exactly that, as apples are only compared to apples. Tom Hopper, who controls Powers’ tire pressures, uses a handheld digital gauge, while Tony Smith uses a Craftsman cordless inflator alone on McDonald’s tires.

Many teams were expecting frozen ground and no mud whatsoever on Sunday. Stu Thorne, manager of the Cannondale-Cyclocrossworld.com team, had cut sipes into the knobs of some Dugast Typhoons in anticipation of seeking grip on the edges of frozen ruts. He also was considering the Dugast Small Bird tires with its numerous small, sharp knobs, with soft, grippy ones on the edges and hard, durable ones in the center, which Johnson premiered at the Derby City Cup stop of the U.S. Gran Prix of Cyclocross series.

Saturday

Temperatures were dropping steadily all day after reaching a high of near 50 at just before midnight Friday. The sun was shining, and the mud was very thick, so there was only one choice: mud tires, and at relatively low pressure due to soft ground and reduced speeds due to the mud suction.

It was the kind of mud that almost pulled your shoes off, and when your shoes did come up, they were twice as big, with mud and grass clinging to them. The top four in U23 men and 17-18 winner Logan Owen (Redline) were all on Limus tires.

Wednesday-Friday

Tire choices were more fluid during the week, as racers arrived Tuesday to find Madison blanketed under deep snow and the course plowed in order to be rideable at all, leaving a firm inch or two on the unpaved sections of the track.

The relatively pristine white snow that greeted Wednesday morning’s non-championship events did not last, as sun and temperatures rising from 21 to 41 kept water flowing out of the snow over the frozen mud below.

There were some super slick corners where a thin coat of mud greased the permafrost underneath, but mostly the corners were either snow or mud and the big descent was straightforward with good traction.

Mixed treads in the morning gave way to mud treads by the final race, in which Adam Craig (Giant) toyed with the singlespeeders. It was slick enough to require most of his downhill skills and then some, though he said he was able to find “a bunch of traction out there.” Air pressure was low for the snow in the morning and to find any kind of traction on the ice later.

Thursday was far slicker. It was 15 overnight, and the day was overcast with a high of 38 and humidity of nearly 100 percent. The ground underneath was rock hard almost everywhere except near the pit area. The surface mud was thin and very slippery.

On Wednesday, sections of snow along the course tape on its eastbound sections had remained firm. But on Thursday, as the afternoon progressed, that snow grew rotten and soft, with slithering tires carving 4-inch-deep tracks and the best lines changing by the minute. The main issue was the ice underneath, however.

I raced at 2 p.m. Thursday and can speak from personal experience about how slippery it was. The defending champ, 25-time national titlist Paul Curley, sported the only non-mud tire in the front two rows of my race (Dugast Typhoons), and he must have crashed a dozen times by the end.

“I saw that and knew it wasn’t going to work,” said winner Bob Downs, a local who knows the course. The 145-pound Downs rode Dugast Rhinos, with 18 psi in the rear and 17 in the front, and never crashed.

I ran 28psi in the rear and 24psi in the front, and if I had a do-over, I would have gone considerably lower despite my 170-pound weight. I crashed so many times I lost count, including once on the big descent, where getting up was a challenge as the line was simply an icy trough.

Friday became wetter yet, as a quarter inch of rain fell overnight. The low of 34 neither helped freeze nor thaw the permafrost, and temperatures rose all day under damp, foggy, heavily overcast skies, reaching a high of 47 at 11:21 p.m. Mud tires at very low pressures were again in order, crashes abounded, and disc brakes were not helping.

Regarding pressure

I want to clarify an error in last week’s article that a number of you pointed out. Here’s one sample:

Dear Lennard,

You rarely make technical blunders in your articles, but you made an odd one with your last cyclocross tire article. You state, “In super-slick conditions, top riders often run close to half that pressure — 17-18 psi. Given that ambient air pressure at sea level is 14 psi, you can see that this is almost flat.”

Ambient air pressure is completely irrelevant as our tire pressure gauges are measuring the difference between tire pressure and ambient pressure (psi gauge).

—Steve

Dear Steve,

Oops. Brain fart. You’re absolutely right. If your gauge says 18 psi (“psig”) you have 18 full pounds per square inch above ambient pressure, not just a few pounds above ambient.

There are two types of pressure gauges. For reading “psi” there is “psia” and “psig,” with psia meaning “pounds per square inch absolute,” and referring to absolute pressure.

However, psia gauges are rare and never used in the bike industry; psig is what all bike pressure gauges read. The abbreviation stands for “pounds per square inch gauge.”

My friend Alan Hills, who works for the National Center for Atmospheric Research, where plenty of attention is placed on air pressure, says, “A psig gauge is two-sided with one side reading the upper pressure (in this case the bike tire) and a second side (the so-called gauge side) referenced to ambient pressure.”

At sea level a bike tire reading 30 psig would have 44.7 psia in the tire 30 psia + 14.7 psia of normal atmospheric pressure. Here in Boulder, 30 psig would be (30 + 12.1 = 42.1 psia).

For a cyclist, psig is the correct value for a gauge to read, because differential pressure is what gives a bike tire its float characteristics. For example, 30 psig in a bike tire — whether at sea level or in the high mountains of Nepal — will ride identically.

― Lennard