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Technical Q&A with Lennard Zinn – Torque techniques, carbon questions and an idea that worked

  • By VeloNews.com
  • Published Mar. 6, 2007
  • Updated Oct. 8, 2010 at 5:19 PM EDT

By Lennard Zinn

Torque
Dear Lennard,
I recently purchased my first full carbon bike, absolutely love it. Yet, I’m scared of over-torquing the seatpost clamp. Is there a torque wrench you could recommend that works on Allen wrenches? What’s the worst that happens, the seatpost clamp needs replacing or I have this fear of the actual seat tube deforming, I’m not doing the Samsonite luggage monkey torque on it, but “hand tighten” is just too open to quantify.
ThomasDear Thomas,
First of all, carbon frames generally have a separate band clamp to tighten the seatpost, and, yes, the worst that can happen, assuming you are using the right size seatpost in it, is that you will strip the threads in the clamp and have to replace it. And any torque wrench “works with Allen wrenches,” as long as it is ¼-inch or ⅜-inch drive (or even ½-inch drive, as long as you have a step-down reducer to ¼-inch or ⅜-inch drive). You simply get Allen wrench bits in ¼-inch or ⅜-inch drive that fit on the square drive end of your torque wrench. Alternatively, for stem bolts, Ritchey now has a slick little torque wrench with a built-in 4mm Allen wrench on it.
LennardThe cosmetics of carbon
Dear Lennard,
I pulled the Giant brand OE carbon fiber seatpost (stock on OCR road and VT mountain bike models, among others) out of my Titanium Raleigh cyclo-cross frame with the intention of using it on a hard tail mountain bike. Unfortunately, the clear coat for the first two or so inches that were inside the seat tube (in what looks like an aluminum shim) is almost opaque, fading to merely cloudy by the bottom. I rode it on the mountain bike this weekend at near full extension and there were no scary cracks or pops, but wonder if its dangerous, or just ugly.Also, is there any way to prevent this discoloration on the new Alpha Q post that’s replacing it?
MarcDear Marc,
The discoloration is most likely just on the clear coat and does not affect the fibers and hence the strength of the post. Probably the galvanic corrosion reaction between the seatpost and the aluminum seat tube sleeve discolored the post. To prevent it from happening on your new post, at a minimum pull it out frequently and grease it (and if it slips use Tacx, Ritchey or FSA carbon assembly paste on it instead). I suppose you could also wrap it with something as was mentioned last week to shield it from the aluminum.
LennardCan you clamp carbon?
Dear Lennard,
I am curious if it is okay to use Park Tool bike stands with carbonfiber seatposts (specifically FSA SLK). Others have said that, “If it can hold up your butt, then it’s strong enough to handle clamping.” This may be true. However, unless I’m doing this riding thing wrong, my butt is putting very different forces on a seatpost that would a bike stand clamp.FSA offers no information on this at their website.
WilliamDear William,
Indeed, your butt does put very different stresses on it than a clamp. That said, while it is certainly true that you never want to clamp one of the frame’s carbon tubes in a bike stand, a seatpost is thicker and stiffer and can stand up to more clamping stress. But any aero seatpost or integrated seat mast should never be clamped in a bike stand, and it’s a good idea in general to do as pro teams do and use a bike stand that supports the bottom bracket and clamps the front or rear dropouts with a quick-release skewer. Try clicking either hereor here for good examples.Using this style of stand eliminates any chance of crushing the seatpost or the frame tubes and it allows time trial bikes and other bikes with non-round tubes and seatposts to be worked on.
LennardCreak?
Dear Lennard,
I recently bought a Basso Diamante that a friend of a friend of a friend put together. I believe the frame set is new. Great bike, but I am getting a creaking or cracking sound when I am aggressive on the pedals. This only occurs when I am seated. I can recreate this by riding in an animated fashion (sloppy/up and down), or if I perform a fast slalom when riding. I also hear this if the road is bumpy or uneven.We’ve changed pedals, seat, seatpost. We’ve checked/tightened the bottom bracket and rear wheel. No luck. We now suspect the inner sleeve in the seat tube.Oh, and one more thing. I am pushing about 250 pounds. Am I too big for this bike?I’d appreciate any ideas.
PaulDear Paul,
It may be the seat tube sleeve, but there are a couple of things to try first. There is a possibility that the seatpost is too long and its bottom end is moving below the sleeve, causing the creak. Try cutting it off so that its bottom end reaches just to the bottom of the seat tube sleeve and no further, when your saddle is the correct height for you.Another thing to try is to see if the creak is caused by the edges of the saddle rubbing on the seatpost clamp. If the leather touches the rails or the clamp when you sit on it, you will get creaking. Try greasing the edges of the saddle to see if it eliminates it.If those measures do not do it, you can try removing the seat tube sleeve, sanding it and the inside of the seat tube, cleaning contacting surfaces with rubbing alcohol, and gluing the sleeve in with epoxy.Certainly your weight will create more movement of parts than wouldthat of a lighter rider. But if the creaking is only happening when you are sitting on the saddle, the creak is not caused by enormous stresses and probably can be eliminated.
LennardA recommendation that worked
Dear Lennard,
I tried the Tacx carbon seatpost paste you recommended and it works great! I had two aluminum and one carbon seatpost that would routinely slip on me. All three received the seatpost paste and all three no longer slip. I’d vote this as a top-five tip of all time!
DavidCool!
Lennard


Technical writer Lennard Zinn is a frame builder (www.zinncycles.com),a former U.S. national team rider and author of several best-selling bookson bikes and bike maintenance including Zinn& the Art of Mountain Bike Maintenance, which is now availableas a 4-hour instructional DVDZinn& the Art of Road Bike Maintenance, and Zinn’s Cycling Primer:Maintenance Tips and Skill Building for Cyclists. Zinn’s regular columnis devoted to addressing readers’ technical questions about bikes, theircare and feeding and how we as riders can use them as comfortably and efficientlyas possible. Readers can send brief technical questions directlyto Zinn. Zinn’s column generally appears here each Tuesday.

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