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Technical FAQ: Swapping cages and rim width follow-ups

Swapping derailleur cages

Dear Lennard,
I’d like to know if it is possible to take the long cage from an Ultegra 6800 rear derailleur and use it to replace the shorter Dura-Ace 9000 cage? 

I’d like to have the ability to run a cassette up to 32 teeth but don’t want to lose the aesthetic by running an Ultegra on an all Dura-Ace drivetrain.
— Jean

Dear Jean,
Yes, you can do that. I have instructions for interchanging Shimano jockey-wheel cages in “Zinn and the Art of Road Bike Maintenance, 5th Edition.”
― Lennard

Grinding freehub feet

Dear Lennard,
Just read your column about 11-speed cassette installation to 10-speed freehub. It’s quite a clear idea, but how did you grind these “little feet” on the freehub? By which tool?

I’m solving same problem — I bought a 105 groupset and am pushing it to work with “Sora-ready” wheels. I regret that I didn’t buy a 10-speed group; I’m now having big difficulties with it.
— Alexander

Dear Alexander,
I just filed them with a hand file. I used a big file and used the side of it to file the feet back.
― Lennard

Feedback on tire pressure and tire diameter

Dear Lennard,
Your last article is very clear, and I’m 100 percent in agreement with your analysis. I’ve had this discussion with friends for years … usually related to FatBike wheels.

If you use the “exaggerated” FatBike tires as a tool to illustrate the magnitude of force involved, I think people visualize it better. A lot of guys over-inflate their FatBike tires to get them seated. Many believe that more pressure always yields lower rolling resistance, so they keep adding air. I have to strongly emphasize to all of my customers to NEVER exceed 20 psi on any fat rim but in reality, they should probably never have more than 12 psi in the tires for any length of time. The tires stretch because the amount of force is so massive. Poor rims will eventually fail after the tires stretch enough. You can lift a truck with these wheels just like an airbag.

When a FatBike tire “lets go,” it is way more dangerous than any skinny tires I’ve experienced. It’s pretty obvious when you think about the number of pumps you put into that tire vs any skinny tire. It is pure stored energy. The sealant will penetrate the skin like a tattoo — ears will ring for hours, your eyes will not have time to blink before the sealant hits the cornea. More than a dozen customers have written me to tell me their experience and embarrassment for not following instructions. On top of that, effective rolling resistance doesn’t change measurably above 12psi for a 170-pound rider.
— Jim Simons
President, FattyStripper.com

Dear Lennard,
I think some readers are confusing pressure and force. Same psi and more square inches equals more pounds of force.

 It’s why you can easily hold 100 psi with your finger if the tube is the size of a valve stem, but that rapidly becomes impossible as the tube ID — and cross-sectional area — becomes larger.
— Peter

Dear Lennard,
I just switched to wider 25mm carbon road rims from the 23mm width carbon rims I had before and installed the same 700 x 28mm tire I had been using on the standard width rims. My 2015 Ridley Fenix used to just allow the 28mm tire to fit, with some scraping on the seat tube when I would get gravel on the tire. With my new wider rims, they have much better clearance using the same tire. I love the ride of 28mm tires, but the scraping was irritating and it took some paint of the back of my seat tube. Wider rims may solve clearance problems for some frames and allow you to use 28mm tires for a softer ride.
— Doug

Still confused about rim width and tire stress? Refer to this PDF >>