Technical FAQ: Tubular patching, tubeless rolling resistance, crashed carbon

Lennard Zinn addresses questions on tubular patching, tubeless rolling resistance, and inspecting crashed carbon for this week's edition of Technical FAQ.

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Tubular patching

Dear Lennard,
I’ve been riding sew-ups since the ’80’s (when a Clement Criterium Seta Extra cost $40 and worth every penny, even when $40 was real money) and have had fair success repairing them when perforated. I have used up the last of my stash of liquid latex (Speedseal from England seems to be no longer available) and wonder if there is a recommended replacement. Is the liquid latex used for molds and Halloween makeup suitable for tire repair such as re-sticking base tape back in place and recoating sidewalls? I have heard that Barge Cement (the brand) is an answer for re-gluing base tape, but it seems that there are various versions of that product. At the recommendation of my local bike shop, I have also tried removing the valve stem and dumping in some tubeless tire sealant with mixed results. If you ride and repair tubulars, what do you use?

Dear Steve,
I have always used Barge Cement to glue the base tape back on after patching a tubular. I have had more success on sealing dried-out sidewalls with Tent Sure than with easily-obtainable liquid latex formulations. And if those really are Clement Criterium Seta Extras from 30-40 years ago, you want to put 303 Protectant on the tread.

Additionally, I no longer patch small leaks—I instead inject Effetto Mariposa Caffe Latex sealant in them through the valve stem (with the valve core removed, although really old tubulars don’t have removable valve cores). I stand the wheel up overnight with the hole down until it seals. The Caffe Latex won’t damage the latex inner tube as much as some sealants and it will fill small leaks.

I often find that, if the hole is big enough, I have to make sure that the hole is down (the sealant will have stained the sidewall where it bleeds out, so it is not hard to find) whenever the bike is sitting for more than a few minutes. If I don’t, I find myself stopping to pump some while I’m out on rides.

And when I get a puncture when I’m out riding, I first try injecting a pressurized sealant bomb like this or this into the valve. I let it stand with the hole side down for a couple of minutes before riding. Only if that does not work do I change the tire (and on most rides, I don’t even bring a spare tubular. I roll the dice and count on the sealant). Peeling a well-glued tubular off of the rim on the side of the road is not my idea of fun.
― Lennard

Tubeless rolling resistance

Dear Lennard,
Do high-end clincher tires with latex tubes have lower rolling resistance than high-end tubeless tires with sealant in them?

Dear Calvin,
Because of the differences in tire construction, there is no blanket answer to this. This article is a few years old and can at least give you an idea.
― Lennard

Acceptable drop out tolerances

Dear Lennard,
I refer to your frame alignment article dated June 2019, specifically the note which discusses acceptable tolerance on frame dropout width.

“If the spacing on the frame is 1mm less or 1.5mm more than nominal, it is acceptable. For instance, if you have a frame whose rear spacing should be 130mm, acceptable spacing is 129–131.5mm.”

Can you please advise if there is a recognized technical standard that outlines these acceptable tolerances? I have a carbon road disc frame using the 12×142 axle standard, however the distance between dropouts measures 144.36mm. The result is that the wheel is not held in place by the dropout lips without the axle bringing the frame together.

Dear Tate,
I have run into the issue quite often of the dropout lips being too far apart to snag both ends of the axle end caps on a through-axle rear hub. As far as I know, there is no agreed upon tolerance for dropout spacing by a standards organization or universally by all frame manufacturers.

Crashed carbon inspection techniques

Dear Lennard,
Great story on your fork and the value of inspections!

We are nearly at our 11,500th customer right now and have invested a lot of time, money and energy into quality inspection techniques. We have performed inspections for OEMs, ProTour riders, and hundreds of everyday riders that have crashed hard or have been hit by a vehicle. Ultrasound is a great method to inspect a carbon fiber object when there is any question. Our inspections start as low as $50 for a basic Ultrasound scan.

Next month I am getting fully NDT and Ultrasound Certified as a Level II inspector as we begin our Ultrasound growth plans!

Shawn Small
Owner || Engineer
Ruckus Composites

Dear Lennard,
Some years ago, when I worked in the Pentagon, I met a materials expert who tested carbon fiber parts in fighter planes. I asked him about the coin test, and about using it to detect damage to carbon bike frames. He said that the test worked well for large panels like those used in airplane fuselages, but that it could not reliably detect damage to small pieces with tightly curved shapes, like those found in a bike frame.

Dear Lennard,
This is not reassuring. Last year my Cannondale Super Six fell, hit the sharp edge of a metal electrical box and put a deep gash in the top tube of the frame. I suspected the frame was toast and disassembled the bike.

After checking with several frame repair shops, I was informed to use the coin test and if it passed, no worries. It passed. So this spring I reassembled the bike and began using it again, as a training bike rather than my road race / group ride bike. (Quit laughing; yes, I do an occasional Senior Olympic Road Race, but as I am always riding alone, I have just about quit RR’s and now spend my time and effort on Senior Olympic Time Trials).

So now, here I am, this summer having put over a thousand miles on this frame. Our roads are rough. The best area to ride just got chip sealed. We have lots of hills and lots of descents and now, I can worry again. However, the bike seems fine, even going through a hill repeats ride.

At the time the bike was damaged my local dealer quoted me a price higher than a comparably equipped Super Six for just a frame. I was a bit put out. They have since revamped their entire bike operation having hired the proprietor of the other local shop after he closed.

Dear Lennard,
Great article. My big take-away is that you need to REALLY REALLY inspect your bike (and helmet) after any crash. In my case, I would need to take it to a shop. I have never worked in a shop but if I did and that fork came across my bench, I would be tempted to put a hacksaw to it before I let it out of my sight.

Dear Lennard,
After a head-on with a dog at close to 30mph and a nasty somersault a few years ago, I removed the fork and cut it in half with a hacksaw before tossing it into the trash. The steel bike was mostly intact but the fork… I had zero confidence in it even with no visible damage and didn’t want someone dumpster diving and sticking a questionable fork on a bike.

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 Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”
He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn