Gear

Technical FAQ: Fixing a misaligned braze-on front derailleur mount

Lennard Zinn instructs on how to deal with a misaligned mount, addresses the advantages of tubeless tires, and explains the sailing effect when riding with the wind.

Dear Lennard,
I am at the finish line on a Colnago Master restoration, and I’m running up against an issue with the front derailleur. It seems the front derailleur braze-on is not aligned correctly. When we tighten the front derailleur, it aligns incorrectly. Do you have any thoughts on a remedy? Frame has already been repainted, so we can’t do anything to the braze-on at this point. We’ve tried three different derailleurs; all have the same issue. Thanks for your input!
— Eric

Dear Eric,
It’s been a few decades since I’ve had reason to do this, and I almost forgot the easy way and at first headed down that shim path with my thinking, too. Instead, using a small, thin flat file, you can easily widen the slot toward the outboard side and allow the derailleur tail to rotate outward until it lines up with the chainrings. You can still blend in the notches you made at the top and bottom corners of the slot look with a thin round file.
― Lennard

Dear Lennard,
In your recent posting about tubeless tires, you wrote, “Another is that energy can be saved by eliminating the inner tube, although this is often more than compensated for by the thicker layer of rubber inside a tubeless tire to prevent air loss.”

In tubeless car tires, the inner layer is, I believe, always butyl rubber, which is very good at retaining air. However, butyl is a high-hysteresis/high-rolling-loss material.

What material is used for the air retention layer in tubeless bike tires?
—Doug

Photo: James Startt

Dear Doug,
Mavic tire engineer Maxime Brunand answered your question this way: “It’s just (the air retention layer) rubber compound. The formula is the secret of each manufacturer, so it’s difficult to elaborate more than that. At the very beginning of tubeless tires, butyl was used, but the rolling resistance of butyl is horrible. And if you wanted the tire to be fully sealed without sealant, you had to use a lot of butyl! So, now it’s just a rubber compound that the sealant will make airtight.”
― Lennard

Dear Lennard,
Millions of words have been written about riding into the wind, but I’ve often wondered about riding with the wind when the wind is blowing above 25mph (which is fairly frequent in Oklahoma). On my ride yesterday I could tell the wind was blowing about 22-23mph as when I reached that speed I was riding in a dead calm. My question is, when riding at speeds below the speed of the wind, say 20 mph, is it more efficient to be as small as possible in order to punch as small a hole as possible through the air, or ride on the hoods a little higher up so that my body acts as a sail? I’m assuming if I rode with a power meter, I could watch the wattage produced, but since I do not, I’m curious to hear your opinion.

I forgot to include an important part of my question. The question is in regards to riding with the wind uphill. Not a super steep hill, but hills less than 5 percent grade. It’s in these instances that I want all the help I can get!
— Tony

Dear Tony,
Until you reach the speed of the tailwind, you are better off sitting up and getting the sail effect. As long as you and the wind are going in the same direction and its speed exceeds yours, you will not “punch as small a hole as possible through the air” by getting smaller, because you won’t be punching any hole whatsoever into the air. Your net speed relative to the wind is still negative until your speed and the tailwind’s speed are equal, and you will be creating a wind shadow in front of you, rather than pushing into the air. Since you’re going uphill, you might as well sit up, open your chest to breathe more easily, and focus on your pedaling dynamics; pedaling ergonomics can be better idealized when sitting up than when getting down into an aero position.

When your speed exceeds that of the tailwind, you will then go faster the more aerodynamic your position. Your aerodynamic drag is calculated based on the difference between your speed and the wind speed when their directions are the same.
― Lennard

Feedback about the previous week’s column

Dear Lennard,
For those who have purchased gravel bikes with 1x drive trains, and who have had an adverse reaction to them, I offer the following: As you noted in your last column, there are a large number of variables to consider when attempting hybrid (brand) drive trains. I bought a 1x Giant Revolt Advanced 1 and didn’t like the somewhat limited gear range, even with a SRAM 10X42 rear cog (42/40=1.05; 10/40=0.25). After looking at the possibilities, I bought a Shimano GRX 2x crank (46,32) w/bottom bracket, a GRX front derailleur, a front bar-end shifter, an 11 x 40 cassette, and a Wolf Tooth RoadLink. I thought it would work, but as you and my LBS point out, 1x rear derailleurs are not usually compatible with 2x drive trains. So, I got a SRAM Force long-cage rear derailleur as well. I can report that this not-too-costly adaptation works nicely. Being an older rider, I appreciate the extended gear range (40/32=1.25; 11/46=0.24) and the smaller gaps in the cog sizes. I run 47mm Teravail Rutlands on a 27.5 wheel in rocky and ‘rooty’ roads and trails, and the bike performs nicely. Finally, thanks to you for your dependable advice on all things cycling!
— Arthur

Dear Arthur,
Thanks for the good tips on widening a 1X drivetrain’s gear range.
― Lennard


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.

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