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Technical FAQ: Cyclocross tire woes

  • By Lennard Zinn
  • Published Nov. 11, 2009
  • Updated Oct. 11, 2010 at 2:30 PM EDT

Flats at the Xilinx race in Longmont, Colorado, got Lennard to thinking. Photo: Brad Kaminski.

Next week I will talk about gluing tubulars to carbon rims, as I promised, but this week I want to address the huge influx of mail I got on flats on the Xilinx cyclocross course, sealant, and on tubeless ’cross tires.

First, on the Xilinx flats I discussed last week, here is the scoop on what caused those and thanks to the many of you who pointed out the problem. I’m sorry for your pain and expense.

Dear Lennard,

I just read your article on flats at the Blue Sky race at Xilinx. I raced that course as well and double-flatted. I was running tubulars. But the flats weren’t caused by thorns. The course had a number of sections that crossed a gravel sidewalk that is lined with metal edging.

That edging is notorious for causing pinch flats. It just cuts right through the tire. I think it was made worse with the mud (at least during my race) since the ground was really soft and the tire would sink even lower than normal before hitting the edging.

Not to mention that you couldn’t even see the edging on the sidewalk located right after the north side of the pit. The promoters put a lot of effort in covering up most sections of edging with carpet, but the course was such a mess and covered in snow the day before the race that I can’t imagine they covered every square inch.

Inspecting my tires after the race I had 2-1/4 inch slits in both tires. Unfortunately, no sealant would have saved my tires.
-Lee

On that subject, a number of people also wrote in saying they got pinch flats, rather than cuts, from that edging. I think that’s what happened to Matt Pacocha’s tire on his ill-timed flat when he was up at the front of the pro race, only to have to ride a half lap on a front flat.

In corresponding directly with a number of them, I questioned the tire pressure they were using, since Tom Ritchey long ago taught me the wisdom of using a narrow tire pumped up hard for riding in mud, since it digs in for traction, puts more force into a smaller area of the ground, and the soft ground makes a hard tire less jarring to ride.

But Stu Thorne, the owner of Cyclocrossworld.com and mechanic for Tim Johnson (who also cut a tire on that edging in warmup), Jeremy Powers and Jamey Driscoll, said this:

Dear Lennard,

For Saturday we ran 28 psi in front and 29 psi rear for all three riders.

Sunday we ran larger 34mm tires for more float in the sand at 26/28 psi. I used to run skinny tires for the same reasons as Ritchey mentions … they seem to get down to the good stuff and also slice through the mud vs. push it.

Ever seen a swamp buggy race? Skinny tires are the norm. But for these courses the 32mm tires at the pressures we ran seem to work best on the varying conditions incurred during each lap — road, grass, packed mud and full-on ankle-deep mud.
-Stu

Now, regarding sealant:

Dear Lennard,

How do you drain the sealant out the tubulars at the end of the season? I’d rather not remove the tires from the rims just for that purpose?

What is the reason to remove? Not sure here in the East sealant is necessary but anything I can do to be more bulletproof is worth it.

I’m a tubi-newbie and found this year the hard way that my Grifo sidewalls became porous after a season. Both went after extremely muddy wet races.

Unfortunately I had never heard of Aqua Seal or the need to maintain my tires.

I asked a couple people this past weekend and they mentioned that with Challenge tires you can’t use AquaSeal without removing the lacquer they put on first. Is this correct? What is the correct way to do so?
-Don

Dear Don,

You can drain almost all of the sealant out by deflating the tire completely with the valve at the bottom. Remove the valve core. Most of it will come out simply with the wheel standing with the valve at the bottom. You can push more out with your thumbs with the wheel almost horizontal and the valve side slightly lower than the other side. Then try to shake the last out of the valve stem. This won’t remove all of it, but that’s okay.

Replace the valve and inflate the tire and spin it occasionally, maybe deflating and re-inflating it a few times during the off-season to prevent the remaining sealant from hardening in a single glob somewhere in your tire.

It’s not critical to remove all of it; you are simply trying to avoid having a lot of sealant turn into a hard glob, adding useless weight and unbalancing your wheel.

As for the AquaSeal, as you probably know, that is particularly important for muddy races and repeated washings when using Dugast tubulars. Challenge and Vittoria tubulars have a pretty good latex coating on the sidewalls, as you know, and the AquaSeal won’t stick well to it.

However, after riding them for a while at low pressures, you will see that crisscross pattern on the sidewalls along the perpendicular directions of the casing threads. This shows that the flexing of the tire is effectively chafing away the latex sealant, and Aqua Seal will now stick to them. I do not recommend using a solvent or an abrasive method to remove the latex.
-Lennard

Dear Lennard,
When I glued my tubies I immediately put Stan’s in them, so they never saw dirt without sealant. Over the last several weeks of racing/training here in Colorado and in Oregon I have not experienced a flat.

I have had several thorns in my wheels, but I just pick them out, or break them off at the tip. Some day when my Fangos die I’m betting I see hundreds of little dots that are remnants of thorns.

The problem with my setup is adding sealant adds weight, and it’s the worst kind – rotational weight at the rims, but the additional weight is marginal. The advantages of tubulars over clinchers and tubeless outweigh the issues of flatting, rolling off the rim and price, in that I have noticed significant increases in my handling and confidence since switching from clinchers.

It seems a lot of people dither on wheel/tire choices and experiment a lot before finally realizing tubies are the way to go. Nowadays you can get a set of Williams tubulars for under $400 and tires for under $100 each, which is pretty good when considering the cost of road racing wheels and tires.
-Todd

Regarding tubeless ’cross tires, I said it a bit too strongly last week when I said the Hutchinson tubeless ’cross tires are “useless for racing cyclocross” since obviously, many people do use them for that, and, as you can see below, riders have come up with some solutions to make them work. That said, in my race in Brighton, Colorado, on Sunday, a guy ahead of me burped a tubeless tire so badly on a 180-degree corner that it made a loud explosion, and he went down.
-Lennard

Dear Lennard,

My daughter and I have been running tubeless ’cross tires all of last season and continue now, racing every weekend and lots of training rides.

We are using primarily Michelin Muds on Mavic Ksyrium ES wheels, no problem with set-ups and have been running 26/28 psi. This season I have set up Reynolds Assaults with the muds. I did have to wrap tape three revolutions before they sealed; also it is imperative to ream the valve opening so it seats and allows that area of the Stan’s rim strip to lock in.

I started using the Caffe latex in lieu of Stan’s, and it seems you need to occasionally clear the valve stem hole — it works so well it seals the opening.
-Bob

Dear Lennard,
I’m running tubeless for cyclocross (Hutchinson Bulldog & Piranha tires) and find the key to success is the rims – I’m using Stan’s ZTR which are specially designed to be run tubeless.

I’ve only had one burp and that’s when I hit a sizable rock during a race. I run pressure in the mid- to high-20s. They don’t have all the benefits of tubulars, but you can change tires far more easily and they are great on dry ground and sand.
-Linda

Dear Lennard,
I’m writing in regards to Greg’s problem with Dura-Ace wheels and Hutchinson tubeless CX tires burping.

I race a lot of ’cross in Norcal and see the same. But the Stan’s rims work brilliantly and they’re very light. I’ve only used the Hutchinson tires (I run 28-36 psi, I weigh 150 pounds) but have not had them burp at all in a year’s use.

I’ve gotten one flat from a sidewall puncture (easily patchable with a UST patch kit). My teammate runs the Stan’s rims with various non-tubeless clinchers, mostly Michelin Mud 2 and Kendas. I think he’s had them burp a little bit, but again it hasn’t been significant.

I suspect it’s Stan’s very wide rim profiles — 27mm I’m pretty sure — that makes the difference. The tradeoff is difficult wheel changes. In any case, there are a lot of folks running tubeless ’cross tires with success. For those of us with less time and money it’s a nice compromise between tubulars and clinchers.
-Brij

Follow Lennard on Twitter at www.twitter.com/lennardzinn


Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, 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.”

Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.

FILED UNDER: Bikes and Tech / Cyclocross / 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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