Technical FAQ with Lennard Zinn: More cyclocross tech questions, answered
Editor’s Note: Lennard loves answering new questions but would like to point out that he’s answered many cyclocross-related tech questions already over the last couple of years. So to save him some time re-typing so he has more time to ponder new problems and work on his dismounts, please peruse all of Lennard’s recent columns about cyclocross tech. There are columns on tubular tire gluing, sealants, brake chatter and more. And if you still have questions, send them on.
Well, cyclocross (along with smoke from a big wildfire) is in the air in Boulder again. The Wednesday Worlds ’cross training ride just started up and was pretty well attended this week despite the bad air quality due to all of that smoke in the air. And the coming of the season immediately resulted in a bunch of questions about gluing tubulars for cyclocross and eliminating brake shudder (a.ka. brake chatter). So we re-posted my brake chatter article from last season and that drew even a couple of more questions.
Wouldn’t a simple solution to brake shudder for a carbon fork be to have a long cable hanger mounted normally at the headset. I would think that would take the issue of the stretching cable out of the equation. Does this make sense? I would have just enough cable exposed for proper brake operation.
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No it would not. The issue is that the length changes between the cantilever bosses and the top of the head tube as the fork flexes. As long as you have the cable hanger attached up there, it doesn’t matter how long it is, you’d get the same effect.
The ideal thing to eliminate any length change would be to have the hanger attached to the fork’s cantilever bosses. That is exactly what suspension forks for rim brakes (which came in during the days of cantilever brakes and before V-brakes) had. They had an arch with an integrated cable hanger, and the arch attached right at the cantilever bosses so there was no length change between the hanger and the cantilever bosses.
Of course, suspension forks for cantilever brakes have to have a cable hanger attached to the lower legs because as they compress or extend, the distance to the head tube or fork crown changes dramatically, and the brakes simply would not work at all with the cable hanger mounted anywhere else.
Vittoria has a new red valve stem on their 320tpi tubular tires that does not have a removable valve core. This seems incredibly annoying, as you cannot add Stan’s sealant once the tire is installed, and if you damage the core you have to take off the tire & replace the $30 valve, vs. replacing the $1 stem.
I am a big fan of using latex sealant in both tubeless & tubular tires & I’m hoping you know of a way around this frustrating new system. For example, does anyone make a ‘female-to-female’ valve extender that would screw on to the Vittoria valve base, and still accept a removable valve core?
Yes, I do know a very simple way around it. You simply use a standard valve extender upside down.
I have a number of these tires with this valve stem that I use for cyclocross, and I use Stan’s and other sealants in them and love them. You simply use a valve extender.
Clicking on the “larger image” from the link above, you’ll see that this is for a standard valve with a removable valve core, and it shows how to put it all back together.
However, on the Vittorias like yours with the long red valve stem, you unscrew the entire stem from the threaded nub sticking out of the tire. You screw on the valve extender upside down so instead of threading its male end down into the valve stem where the valve core was, you thread its female end over the stub sticking up from the tire. You’d squirt your sealant in at this point. Then you simply thread the red valve stem down over the male end of the valve extender, and voilá, you have a tubular tire that can accept Stan’s sealant.
I have read the VeloNews articles on ‘cross tire selection, yet there are some new tires on the market that make my choice for a back wheel set a bit trickier. I raced Challenge 32mm Fango tubulars last year, and will so again this season. For backup wheels (and for rocky courses, which we have a few of here in Georgia) I was considering the Fango clincher, or one of lower end Tufo Primus (not the Flexus version). My interest is easy reparability (clincher or tubular that works well with sealant). In your opinion, which tire would ride better — a high thread count clincher (260tpi) or a low thread count tubular (60tpi)?
By the way, I have read your articles in VeloNews about sealants, and found them very helpful.
Well, that’s a good question. I would guess that the tubular would still have the advantage due to pressure considerations. You can run the tubular at lower pressure, since the fear of pinch flatting is already lower for a tubular (no sharp rim edges), and it is non-existent for a Tufo, since it has no tube to pinch. And on side hills and rocky courses, the lower pressure will be a distinct advantage for both traction and rolling resistance.
Follow up from two weeks ago:
In my column from August 27, I neglected to point out that on some carbon steerers, the top cap is integral to the expander plug, and I got some feedback on that, most importantly from the horse’s mouth.
I’m pretty sure Kyle is talking about my bike (as I’m the only guy I know not running one on the mtb circuit) in your VN tech questions. His last question was skipped though. For carbon steer tubes, expander bolts often do serve a structural purpose and should not be removed. Aluminum steer tubes are another story.
And for adjustment, I just keep a carbon expander bolt in the toolbox.
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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. Zinn’s column appears here each Tuesday.