Gear

Technical FAQ: Tubeless sealant in tubulars, SRAM front derailleurs, and tire pressure

VeloNews technical expert examines using Mastik tape and tubeless sealant with tubular tires, how to adjust a SRAM front derailleur, and more.

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

Dear Lennard,
I am washing the dust off of my 1982 Colnago and 1984 DeRosa. I haven’t ridden them for at least 20 years. Back in the day I enjoyed riding tubulars, but the damage from goat head thorns were too costly for me, and I had a set of clinchers built around Phil Wood hubs and that served me well until I hung up the bikes.

So, after reading the column for a while, I am guessing I can do the following to ride my tubulars and experience less flats with the same enjoyment. Now I can easily mount my tubulars with the double-sided tape, and then I can add the Caffelatex sealant (which is ok for the latex tubes). Do I need to remove the valve to insert the sealant?

Then, I’d ride frequently to keep the sealant moving around. It seems that you were handling your cross tires this way. I also found some tubulars that I have stored in a box away from heat and ozone.

They look good. Do you think:
1. There is any problem riding them?
2. Will they have removable valve stems? (how can one tell if they are removable?)

Any other tips or warnings would be appreciated.
— Paul

Dear Paul,
In principle, yes, you can do this, and new tubulars kept in a cool dark place protected also from ozone should be great to ride. Some details:
1. Do not use the Belgian tape alone as a way to glue your tires on; that tape works great when combined with multiple layers of glue, making it more work than just gluing, not less. If you want to avoid rim cement and have your tires held on well, then instead use Carogna tape by Effetto Mariposa.
2. Yes, you can use Caffelatex in tubulars; unlike some other sealants, it won’t damage the latex inner tube.
3. Yes, you should remove the valve core and inject the sealant with a syringe or squirt bottle into the valve stem.
4. You can tell if the valve core is removable if the little threads that the valve cap threads onto have a pair of flats on them for a valve core key or cylindrical valve core removal tool. If your well-cured tubulars are 20 or more years old, they might not have a removable valve core. In that case, you can inject the Caffelatex right through the valve. It will go in okay; the problem will be that over time it will tend to gum up the valve and make it slower to get air into it when pumping. If that happens with a removable valve core, it’s no problem; you just remove the valve core, rub the congealed sealant off of it with your fingers and screw it back in.
5. While I used to put sealant in all of my cyclocross tubulars from the get-go, I stopped doing that, because there is only one CX course around here where goats head thorns are ubiquitous. I instead waited until I actually got a thorn in my tire (the leak while the thorn was still in the tire was slow enough that it was no problem to get back to the pit for my spare bike) before putting any sealant in the tubular. I found that I could often go through an entire season without needing sealant in any of my tubulars.

With road tubulars, I also wait until I develop a slow leak before injecting sealant in them. I have a pair of 700C X 40mm tubulars on my gravel road bike right now. The front one has no sealant in it, and I have ridden that tire for at least six months. The rear one developed a slow leak after three months of riding on it or so, and then I put in sealant. Now both of them hold air well and do the normal gradual bleed-down overnight of latex tubes at the same rate.
― Lennard

Dear Lennard,
I’ve been troubleshooting an issue with my Red 22 Yaw mechanical FD for quite some time. The inside of the FD cage has a rounded tab that is perpendicular to the chain. SRAM is telling me that this tab is necessary to move the chain when shifting big ring to small ring. However, because this tab occupies nearly half the available space in the cage, and allegedly due to the chainstay length on my 2013 Cervélo R3, the Yaw feature will not work. Any sort of micro-adjustment to get the chain so it doesn’t rub in the big ring and the 32-tooth cassette (which Yaw is supposed to allow) means the chain is rubbing on the inside cage plate or on the tab. SRAM is standing by the Yaw design, but from what I can see not all their Yaw front derailleurs have this tab. I’ve had several mechanics try to get it to work and the front derailleur is otherwise aligned properly using the 3 guide marks – 2 on top of the cage and the 1 on the inside.

Do you know what the tab is for?
— Chris

Dear Chris,
I’m not familiar with a tab filling half of the space between the cage plates. The leading edge of the outer cage plate on Red 22 and Force 22 Yaw front derailleurs is bent inward a millimeter or two relative to the tail of the plate; this inward bend certainly doesn’t take up half of the space between the plates. It also doesn’t look to me like a “rounded tab.” The Red 22 front derailleur is no longer made, and the outer plate of the Force 22 and Rival 22 front derailleurs is shaped a bit differently than the SRAM Red 22 cage.

If that inward bend in the outer plate is the tab to which you are referring, it indeed is there to kick the chain onto the inner chainring faster.

The Yaw design causes the front derailleur cage to rotate while it moves laterally and thus maintain a more parallel alignment with the chain throughout its range (ostensibly eliminating the need for a trim adjustment). If your chainstays are very short, then the chain angles on your bike in the small/small and big/big combinations will be larger than the amount the Yaw system rotates the cage, and there will continue to be chain rub in big-to-big.
― Lennard

Dear Lennard,
Regarding your last tech FAQs column in VeloNews about Chloé Dygert’s crash, you may want to explain to Ray that F = P x A.
— Matt

Dear Matt,
Yes, pressure is force per unit area, which I should have said explicitly, rather than just describing that relationship verbally as I did. The units reveal this relationship; for instance, PSI is pounds per square inch. (Pounds is a measure of force, not of mass as it is incorrectly often interpreted.)
― Lennard

Dear Lennard,
Another way to think about this is the relationship between psi, square inches, and pounds of force: You can get 90 lbs force with 1 square inch at 90 psi, with 2 square inches at 45 psi, with 0.5 square inches at 180 psi, etc.

As long as there’s enough pressure to keep the rim from bottoming out, the footprint area will change as needed to support the load at a given pressure.

Sidewall and tread stiffness do have an effect, but it is usually small relative to pressure.
— Peter


Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), 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 on Twitter.