Technical FAQ: Don’t melt that carbon seat tube

Lennard Zinn answers reader questions on melting carbon

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Editor’s Note: Lennard 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.

Dear Lennard,
I own a 2006 Orbea Orca, and the aluminum seatpost insert has cracked horizontally right where it meets the top of the carbon frame. I need to remove the insert and replace it with a new one. Orbea indicates that it is bonded to the frame.

The insert is cracked horizontally right at the point where it goes into the carbon frame. The crack is approximately halfway around the circumference of the insert. I am concerned that tightening the seatpost clamp will cause it to break completely — particularly when I am riding — potentially causing loss of control. Although the seat would not go anywhere vertically, it would move side-to-side since the seat tube is no longer clamped to a bonded-in-place seat sleeve. I have a replacement insert. Can I heat the existing insert (from the inside) and break the bond (epoxy?), which will allow me to remove it?

Any suggestions on how to remove it or other alternatives to consider?  I am retired and cost is a concern.
— Ed

Dear Ed,
What about just cutting the sleeve off flush and getting a seat binder clamp that slips over the top of the seat tube?

I would sure rather do that than heat the seat tube, which would be hard to control. Above a certain temperature, you will certainly damage the matrix. While I’m sure you’ll be careful, once you get it warm enough to budge the upper part but not the deeper part, the temptation will be to keep heating to free it, and it will be hard to avoid overheating the upper part of the seat tube in the process.

Of course, you could first try to yank out the sleeve without any heat. I doubt it would budge, and you could tear off the top edge. But I’m recommending cutting that off anyway…
― Lennard

Dear Lennard,
I have purchased a new pair of cycling shoes and will be mounting new cleats on them. If a rider has feet that are slightly different sizes (mine are about 1/2 size different) how should the cleats be mounted to compensate for the different locations of the balls of the feet?  The shoes are the same size, but assuming that the heel is held firmly in the heel cup, the ball of one foot will be in a different location (albeit slightly) than the ball of the other foot. If I mount the cleats so that both feet are properly positioned over the spindle of the pedal, then the heel locations and ankle locations are slightly off. Which would be the preferred compensation? Locate the balls of the feet slightly differently over the spindles so that the heels and ankles are rotating similarly, or center both feet over the spindles so that the heels/ankles are slightly out of sync?
— Augis

Dear Augis,
I passed your question on to Dr. Andy Pruitt, the guru of bike fit and 3D bike fit video analysis, and founder of the Boulder Center for Sports Medicine. He has a rule of thumb about cleat position for different sized left and right feet. He says, “You measure the distance from the heel to the first MP joint on the short foot and that is the cleat placement for both. You can then do the math for a new neutral cleat position if desired.” The First MP joint (Metacarpophalangeal joint) is the joint at the base of the big toe.

In other words, you don’t want to change the length of the lever arm from the heel to the cleat, but you can have more foot length extending forward of the cleat on one side than on the other.
― Lennard

Dear Lennard,
I have the Apex group from SRAM. I’m currently set up with the 11-32 cassette. My chain is about worn, and I would like to replace the chain and cassette. I was looking at picking up a SRAM PG-70 11-25 cassette. Will I need to change out my derailleur as well and go with a short cage, or is Apex derailleur compatible with the 11-25 cassette?
— Nathan

Dear Nathan,
I assume you mean an 11-25 SRAM PG 1070 cassette. There is no reason to switch out your derailleur for that cassette. The Apex derailleur will work just fine, with your existing chain.
― Lennard

Dear Lennard.
I am a big fan and about 10 years ago we finished side-by-side at the Birkebeiner ski race.

Anyhow, this year I got myself a pair of Shimano Ultegra tubeless wheels and Hutchinson tubeless Fusion tires. After adding a little Stan’s, soaping the bead and getting the tire on, the front blew off when I was near 90 pounds. I put it back on with less pressure.

On my third or fourth ride, the rear blew off while riding on a smooth, flat surface. I wasn’t hurt, but the “bang” sure was scary.

Have you heard of bad batches of tubeless tires?  I soaped up the bead like I would do to a mountain bike tire and it all appeared fine. Any idea what might have caused my bad luck and am I safe to try another set of tubeless tires?
— Timothy

Dear Timothy,
I have not heard of this with tubeless-specific road wheels and tires. I have found the beadlock ridge on the rim ledge to be quite effective at keeping the tire on the rim, even when riding it deflated.

That said, you can imagine that there is no instance where it is more important than with road tubeless tires to have absolute precision of the tire bead diameter and rim bead seat diameter. If the tire bead diameter is too big or the bead seat diameter of the rim is too small, there’s a very great danger of blowing the tire off of the rim. On a normal clincher setup, you have an inflated inner tube pushing outward, forcing the bead under the edge of the rim hook. With a tubeless tire, there is high pressure trying to yank the tire straight up off of the rim hooks, and there is no tube working to hold the tire beads outward under the rim hooks. So a non-stretch tire bead that is exactly sized to fit the rim is imperative (carbon fiber beads are chosen for this reason in Hutchinson road tubeless tires). I can only postulate that either the tires or the rims (or both) were out of spec.

For somebody like me who rides tubeless road tires constantly, I find this news disconcerting. But my overwhelmingly positive experience with lots of road tubeless tires leads me to think that you’re safe to try a new set of those tires. I doubt you’d have a problem. Your old ones might be worth trying a warranty claim with Hutchinson.

Last month (April), my daughter and I raced all of our local spring half-dirt road races (Boulder-Roubaix, Mead-Roubaix, and Koppenberg) on tubeless road tires (she on Hutchinson Atoms, I on Fusion 3s) without the slightest problem, including finishing Mead-Roubaix with an earring stuck straight into my front tire. In order to go straight into my tire that way, the earring must have been standing upright, post facing up, in the dirt road. The earring post wasn’t even bent; it was pushed all of the way into the tire, and the tire hadn’t lost a bit of pressure! In those races with so much dirt and gravel traversed at high speed, riders were constantly pulling over with flat tires (but we weren’t!). Maybe one of them found the mate to the earring that ended up in my tire. That would be an expensive earring on a tubular tire…
― Lennard

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