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Road Gear

Technical FAQ: Titanium spindle loads, injecting sealant into inner tubes, finish lines

VeloNews tech expert continues a discussion about titanium spindles for heavier riders, tubeless sealant in tubes, and more about finishline cameras.

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Have a question for Lennard? Please email him at to be included in Technical FAQ.

Dear Lennard,
Regarding the breaking of titanium spindles by heavier riders; I don’t think that the power output has anything to do with the breakage, because the forces aren’t that great. I think that the real issue is shock loading. For example, when you stand up a bit before hitting a pothole or other road obstacle. When you hit the hole, you get a multi-g impulse load that is much larger for a heavy rider than a light one. I think that is when you are likely to break a spindle.
— David

Dear David,
Very good point. Thanks.
― Lennard

Dear Lennard,
I read your recent comment about max load on Ti pedal spindles with interest. The reason a cyclist’s weight is key to pedal capacity is that the cyclist’s weight represents very nearly the maximum load one can exert on a pedal. Dynamic loads while sprinting or impact loads when standing on a pedal and hitting a bump increase the load beyond the cyclist’s weight. But the dynamic or impact loads are still proportional to the cyclist’s weight.
— Bob

Thanks, Bob.
― Lennard

Dear Lennard,
I just finished reading today’s Tech FAQ with the question about sealant in tubes to prevent a sudden blowout. While I’m guessing you’re correct about it not working on a butyl tube (I’ve never tried that combo) I can say that my decade-plus of experience using Effetto Mariposa Caffelatex inside latex tubes (Challenge and Vittoria brands) has helped prevent any blowouts, and most flats, to date — including on severely potholed Minneapolis, MN roads and incredibly rough, debris-strewn Portland, OR roads.

In one case, I got a front flat using a sealant-filled latex tube that was leaking fast enough to be noticeable, but still slow enough to ride safely to a spot to pull over away from traffic. Put a new butyl tube in after thinking I had found the offending object in the tire. Pumped it up, took off and within 100 meters, that tube went flat so fast that I was instantly riding on a thin layer of rubber on the rim. It had been so long since I had flatted with a butyl tube that I had forgotten how scary-fast they can deflate.

After finding that offending object and getting on my way again, I made certain to put a replacement latex tube and sealant in as soon as I got home. For your reader looking to avoid rapid blowouts, I would highly recommend latex tubes, knowing that Caffelatex is safe for them. (I’m sure you’ll have the chemistry to explain that; I just know it works.) It costs more initially, but the smoother ride and fewer flats make up for it for me.
— Andy

A 60ml squeeze package of Caffelatex tire sealant. Photo: Lennard Zinn |

Dear Andy,
If you have had that much success with latex tubes and Caffélatex, there is certainly no good reason to change your methods.
― Lennard

Dear Lennard,
With the increasing popularity of tubeless (and its need of a quick inflation blast) plus the room afforded by wider rims is it time to consider a new, larger inflation valve standard? Maybe something in between Presta and Schrader? Curious of your thoughts on the matter.

Thanks for giving me something to look forward to on Tuesday mornings!
— Kimball

Dear Kimball,
Have you tried seating tubeless tires with Presta tubes by removing the valve core? I’ve never felt that flow through a Presta valve without a core in it restricted airflow enough to hamper tire seating, even on a fat bike.

And while I think a somewhat larger valve would be an improvement on larger tubeless tires, I can’t imagine the bike industry going through the massive upheaval it would take to switch to a different standard. I guess modern pump chucks can switch from Presta to Schrader without disassembling the chuck, so maybe it wouldn’t be such a big deal to add another valve standard.
― Lennard

Dear Lennard,
Thanks yet again for your fascinating column. Regarding latex sealant in tubes, I have (another) anecdote. About two years ago, I suffered a pinch flat during a descent that resulted in immediate deflation and a painful trip to the pavement. That should not have happened on properly inflated 25mm tires.

The tire was almost certainly underinflated, as the bike felt just a bit funny on the descent (yeah, I should have stopped). Afterward, I discovered that my old pump’s gauge was reading 20 psi too high! But the bike had felt OK until shortly before the crash.

My guess is I had gotten a small puncture that resulted in slow deflation, leading to the pinch flat while cornering clumsily. Unfortunately, I did not test the tube for another little hole, so I can’t be sure. Had I had sealant in the tube, it would not have sealed the pinch flat, but it might have prevented it from happening.

I’m still not using sealant, but the real moral of the story is: Pay attention to what the bike is telling you!
— Jon

Dear Lennard,
Thanks for the comprehensive explanation of finish line cameras. Just one very small thought to add, in the case where the edges of the pavement are not parallel at the finish line, one way to go would be to establish the alignment of the road. The centerline or alignment of the road could be established by finding the midpoint of the pavement at the finish line and then establishing the center of the pavement, say 50 feet back on the course. Using a right-angle survey prism, standing over the finish line point, align with the second point and establish two points at the end of the pavement on the finish line. These would be perpendicular to the center. A quick check to make sure nothing is wrong would be to stretch a string line to make the finish line and confirm all three points are on the same line. I admit this is only an incremental (if that) improvement over using the barriers or just using judgment to develop a perpendicular finish line. Again, excellent article. I appreciate all the clarity you bring to a variety of issues.
— Tim

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder ( and purveyor of non-custom huge bikes (, a former U.S. national team rider, co-author of The Haywire Heart,” and author of many bicycle books including Zinn and the Art of Road Bike Maintenance,”DVD, as well as Zinn and the Art of Triathlon Bikesand Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn on Twitter.

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