Technical FAQ with Lennard Zinn: Chain suck, wide range and when to seal

Dear Lennard,
I have a 2010 Orbea Orca bought about nine months ago and have been having problems with chain-suck. The bike shop where I bought it from cannot for the life of them seem to fix it.

I am running all SRAM Red components, Compact Double, even the chain is SRAM. When I downshift from the large chain ring to the small, I will occasionally have a chain-suck, especially if I need to shift under load. The whole drive train freezes up, makes a horrible noise and in some cases I have to dismount and fix the chain in order to get under away.

I have been told by a bike shop technician that SRAM Red is prone to chain-suck. Are there any fixes from the manufacturer or bike shop that I need to be aware of? I’m concerned, since  chain-suck can obviously damage frames, especially carbon frames like mine.
Dan

Dear Dan,
I haven’t had that problem, but we all saw it happen in the Tour to Andy Schleck. His chain got sucked 3km from the summit of the final climb of stage 16, the hors categorie Port de Balès.

That said, Schleck was not using the standard Red setup. Rather, he was using a non-standard 38-53 chainring combination on his SRAM Red crank and non-standard oversized Berner jockey wheels and cage on his SRAM Red rear derailleur. Furthermore, he was in a cross-over gear of 38 X 12, which significantly increases the likelihood of it happening.

In your case, I would strongly recommend checking your chainrings for damage and your chain for signs of wear. Replace your chain as soon as a chain gauge indicates it has significant elongation (a Rohloff Caliber chain gauge drops in on the “A” side, for example); an elongated chain will have a harder time releasing from the bottom of the chainring teeth. And tighten the rear derailleur b-screw and shorten the chain to get more tension on the bottom section of chain.

You should also check your chain line and make doubly certain that the lower limit screw on your front derailleur is properly adjusted.

Lennard

Dear Lennard,
I have a SRAM Red group on my bike. The crankset is 55/42, which I like. My question is what is the downside of putting a PG1070 SRAM 11/32 cassette in the back (with a mid-length Rival derailleur, since all derailleurs in RED/FORCE lines are short)? It seems like it will have best of both worlds, with nice big gears for criteriums and high cadence for hill climb races.
Erhan

Dear Erhan,
There is no downside, other than a bit of extra weight and slightly less crisp shifting and perhaps some aesthetic concerns. But it will still shift fine.
Lennard

Dear Lennard,
I’ve currently got an FSA compact crank (50-34). I had a mixed Dura Ace/Ultegra 9-speed drivetrain with this, with a 27-12 rear cassette. Everything was happy, but I just upgraded to Dura Ace 10-speed to eliminate the mixed group. I now get a kind of grinding sound when in my 34 chainring and either my 27 or 25 rear cogs (my two largest rear cogs).

I’ve had it adjusted at my local shop with little success, and it appears to either be coming from the chain trying to seat on the 34 in front, or the first pulley on the rear derailleur. We adjusted to make sure it isn’t any rubbing on the front derailleur, which it clearly isn’t. I’m wondering what might be the cause, and if something about the new Shimano Compact Crank might help address this issue, since it supposedly works better with their Dura Ace 10-speed chain?

One note…it is only noticeable when under load, namely when I’m climbing, and you don’t really want to listen to any grinding. Also, would this tend to quiet down as the chain/gearing works in? I’ve only ridden it a couple times since the component swap.
Dave

Dear Dave.
Well, since you didn’t mention the b-screw, I will. The b-screw on the rear derailleur, behind the tab on the frame’s rear derailleur hanger, adjusts how close the upper jockey wheel comes to the cogs. I wouldn’t doubt it if the noise you’re hearing isn’t the chain pinched between the upper jockey wheel and the large cogs. If you tighten down on the b-screw to pull the rear derailleur back in a clockwise direction away from the cogs, you might get rid of the noise.
Lennard

Dear Lennard,
I have finally graduated to the exclusive use of tubular tyres for road use! My question is in regards to the wonderful Tufo sealant (please let me know if your experiences have shown better products) and whether or not I can pre-install the sealant in my spare tyre? Will it go dry? How long until it goes dry? It seems like a good idea to have it already in my spare should I flat, but if it’s not going to serve its purpose, then obviously it would be pointless.
Thomas

Dear Thomas,
I wouldn’t put sealant in until after you actually glue the tire on. You hope that your spare tubular sits a long time, unused. During that time, the sealant could get dried out.

I always remove the sealant from my cyclocross tubulars at the end of the season to prevent the sealant from hardening up inside of the tires. If you have ever left a tubeless mountain bike tire deflated for months with sealant in there, you’ll know the problem—the stuff dries up in a thick slab at the gravitational bottom of the tire where it pooled up while liquid. It’s easy to get out of a tubeless tire, but you don’t want that to happen inside your tubulars.

As for types, I’ve only used Tufo sealant in Tufo tubulars. In other tubulars, I’ve only used Effetto Mariposa’s Caffelatex. I’ve heard unconfirmed stories about using other sealants in tubulars (with latex inner tubes) somehow bleeding through and causing the base tape to peel off of the tire. That certainly has not happened to me in years of using Caffelatex in tubulars, but I haven’t tried any other sealants in tubulars, so I can’t confirm or refute those claims.
Lennard

Dear Lennard,
One has to question the benefit of filling tires with N2 since air is 78.09 percent nitrogen, 20.95 percent oxygen, 0.93 percent argon, 0.039 percent carbon dioxide.

Prestacycle claims that “a tire holds nitrogen pressure six times longer than it does with air.” Assuming for the sake of argument that their claim is true, then the initial lost pressure would have to be composed of almost exclusively of O2, leaving a tire that is almost all N2, and since air is about 4/5 N2 the leak down pressure to when the tire is almost all N2 would be about 4/5 the original pressure, 100 psi leaking to 80 psi, not a show stopper. When the 20 percent that is lost is replaced with air that is again about 80 percent N2, the tire would be about 96 percent N2 and 4 percent O2. You can see where we are going. So pump your tires up with air, then fill the initial leak down again with air, and pretty soon your tire is almost all N2 if Prestacycle’s claim is true.
Paul

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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. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.