Silencing Rim Rattles & Checking Sealant Levels

No Oil, TPU tubes

Regarding Carl’s waxed chain getting oiled by an uninformed bike shop employee:

Dear Lennard,

Last time I ordered wax from Molten Speed Wax I got their “no oil” stickers that go on the drive side chain stay.

Patrick

Dear Patrick,

Thanks for pointing that out! One of those stickers was on my package of Molten Speed Wax, and it didn't occur to me that one like could go on the chainstay to warn against applying oil on the chain. I just thought it was a cute sticker.

Sticking one of those on the chainstay is a great idea to hopefully prevent others from having their chains unexpectedly oiled as Carl did.

― Lennard

Regarding checking the sealant level in a tubeless tire:

Dear Lennard,

As another simple check of tire sealant loss without removing the pressure and valve stem, I periodically weigh a wheel assembly and compare it to the weight when its sealant was last topped off. I’ve found that the weight of lost sealant is about equal to the weight of water, 1 gram per milliliter. My digital hanging scale is accurate enough to detect a 10 or 20 ml loss - about what I typically lose per month with my setups. Occasionally I notice a larger than normal loss, probably because I’ve had a puncture that bled sealant while it quickly sealed itself. While this method wouldn’t be useful in a retail shop environment because the benchmark weight of a customer’s wheel assembly wouldn’t be known, it has been a very convenient way to keep track of sealant levels in my own several tubeless wheel sets through each season of the last five years.

Bill

Dear Bill,

That’s an elegant solution well suited to riders who have an accurate scale and use it.

― Lennard

Regarding TPU inner tubes:

Dear Lennard,

Thanks. Good information. I have been using TPU tubes in a few tires. Have had good luck with no flats. Only issue is all my pumps have trouble staying on tubes when inflating Tubolito was brand that was issue. Vittoria had no issues. Takes two of us to fill tires.

Kim

Dear Kim,

That skinny plastic valve stem on a Tubolito TPU tube I was carrying as a spare caused me big problems on a ride once, too, but in a different way. When I flatted the latex tube inside my tire, I discovered that my carbon rim was too deep for the Tubolito valve to reach through. As is my normal custom in such circumstances, I tried to remove the valve core so I could add a threaded valve extender (which I always bring along) so that I could pump it up. Unbeknownst to me, even though the valve core had wrench flats on it, it was not screwed into that plastic valve stem! That was a bummer of a surprise. Rather, the valve core was just glued in, and my spare tube became useless when I broke the glue bond by rotating it with a valve core remover. I was on a dirt road high in the mountains above Boulder and ended up hitchhiking home. I was lucky to get a ride and have not used a Tubolito tube since, no matter how light they are.

― Lennard

Dear Lennard,

I had a catastrophic front flat using TPU tubes a few years ago. Fortunately, I was going uphill as I was doing hill repeats. The tube ripped trying to "stretch" around a spoke hole indent of my rim strip. I was running a 38mm tire and the correct sized tube at about 50 psi. I'll never trust them again.

Ron

Dear Ron,

Yikes! Glad you were not descending!

― Lennard

Dear Lennard,

I recently solved an annoying clicking sound coming from my front wheel and want to share my experience. About 8 months ago I purchased a set of Synchros road wheels that were a new bike takeoff, no use or very little. They are Synchros RR 2.0 Disc, aluminum rims, 28 hole, 21mm internal diameter. They were tubed; I set them up tubeless with 28mm TR tires and all worked as intended, but I noticed a "clicking" sound on each rotation of the front wheel. It wasn't too noticeable, so I ignored it. Over time it came and went; then when I mounted new rubber on the front it became more pronounced. My diagnosis considered, then eliminated, the tire and rim tape. After reading through internet posts, my new theory involved the "puck" or piece of aluminum used to join aluminum rims at the seam. I read that sometimes this clicking can be stopped by inserting foam or epoxy to secure the loose puck. I had a can of spray foam used to seal openings in an RV or car body to prevent critter entry (branded as Great Stuff PestBlock). I sprayed a small amount into the one of the spoke holes adjacent to the seam in each direction. After letting it dry overnight, my ride the next day was blissfully quiet. The foam weighs next to nothing, so there was no impact on the wheel balance. So pleased it worked!

Chuck

Dear Chuck,

Nice fix! Glad it worked.

As a note of clarification, I imagine that this fix primarily applies to “pinned” rims—where the rim is held together by one or more short metal pieces pressed into spaces in the rim extrusion under the rim valley on either side of the seam that create a splint across the seam. The seam will be visible as a thin line that you can feel with your fingers. The metal piece(s) holding the rim together can be a flat piece of aluminum or cylindrical pins; I imagine this is what you have called the “puck.” With the flat plate splint, there may be a dent in the rim bed on either side of the seam to make a bump on the underside of the rim bed to secure the splint in place so it doesn’t rattle around.

Pinning or splinting is not the only way to connect a metal rim; many high-end aluminum rims are instead welded together. The weld is not created by passing an arc from welding torch head over the seam and adding welding rod like bike frame joints are welded. Rather, high current is sent through the rim while the rim is being pushed together from either side of the rim, and the rim material itself melts at the seam and creates the weld as well as a ridge of weld flashing that sticks out to the outside as well as in the inside of the rim.

The rim decreases in circumference during welding, since material on either side of the seam is consumed in creating the weld; this is carefully calculated so that the rim ends up being the correct circumference. The ridge of weld flashing is ground off on the outside of the rim and in the rim valley, creating a signature small depression that identifies it as a welded rim.

While it’s possible to imagine some of the weld flashing in a welded rim breaking off inside and rattling around, I have never experienced it. If so, your spray foam fix might work then, too.

― Lennard

Subscribers can send brief technical questions to Lennard at: veloqna@comcast.net.

As a frame builder, Lennard Zinn has been designing and building custom bicycles for over 42 years; he founded Zinn Cycles in 1982 and co-founded Clydesdale Bicycles in 2017. His Tech Q&A column on Substack follows his 35-year stint as a technical writer for VeloNews (from 1987 through 2022). He is a former U.S. National Cycling Team member and author of many bicycle books including Zinn and the Art of Mountain Bike Maintenance, Zinn and the Art of Road Bike Maintenance, and The Haywire Heart. He holds a bachelor’s degree in physics from Colorado College.

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