Tech & Wearables

Technical FAQ: Shimano GRX chainrings, tubeless-ready road tires with tubes, rivnuts

Lennard answers questions about Shimano GRX drivetrain compatibility, tubeless-ready tires on standard rims, and how to manage sticky bottle-bosses.

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

Dear Lennard,
I bought your road maintenance book in 2007, and I still refer to its grease-smudged pages with some frequency.

I’m currently trying to make it a little easier for me to get my 2018 Surly Straggler up some of those gravel hills (I just hit Medicare age). It has a Shimano 105 groupset with a 50/34 crankset and an 11-speed 11/32 cassette.

I just bought a Shimano GRX FC-RX600 46/30t 11-Speed Crankset. It sounds like my current 105 shifters will still work. Do I need to get a GRX RD-RX810 11-speed rear derailleur or can I use the105? And can I still use my 105 front derailleur? You may have guessed that I’m trying to keep the cost down.
– Tim

Dear Tim,
The 105 rear derailleur should work fine. I doubt that the 16-tooth jump on the front with the GRX crank is enough bigger than your current 14-tooth front jump to cause it any problems.

The front derailleur is a different story, however. There are two issues with the GRX crank that will be problematic for the 105 front derailleur. The first one is that the chainrings are so much smaller than the cage of the front derailleur will be far away from the chainring for much of its length, because its curvature is matched to a much bigger chainring. The second is that the chainline of the GRX crank is 2.5mm further outboard than that of standard road cranks. Your 105 front derailleur was not designed to operate that far away from the frame. My guess is that you will have to resort to a GRX front derailleur to get this system to work acceptably. Fortunately, front derailleurs don’t usually break the bank, although the pandemic has made them hard to find.
― Lennard

Dear Lennard,
I have a question about tires. Recently, I’ve been using a set of Mavic tubeless-ready rims and Mavic tires that came mounted on the rims. I’ve loved the ride and feel of the setup.

My question is, can tubeless-ready tires be mounted to “old” style hooked-bead rims with an innertube?

Or should I just keep like to like: UST tires to UST rims and regular clincher tires to hook bead rims with inner tubes?
— Peter

Dear Peter,
Tubeless-ready 700C tires can be mounted on 700C hook-bead rims with inner tubes.
― Lennard

Dear Lennard,
My wife used to race and has an old 2001 Schwinn Homegrown Factory that now fits my 11-year-old son. He is going to do a little bit of ’cross on it this fall. I attempted to remove the bottle cages, and one of the mounting bolts just spins and spins. I assume it is stripped. I can’t get it to ‘let go’ of the frame, so I can’t remove the bottle cage! Any inside tips on how to get this out so I can remove the bottle cage? After I get it off, will there be any hope of fixing it so I can put it back on in the spring?

Thanks for all your help over the years.
— Tim

Dear Tim,
I doubt the bolt is stripped. I think what has happened is that the rivet nut, a.k.a. “rivnut” that serves as the threaded bottle boss has wiggled loose from the wall of the tube and just spins freely when you turn the bolt. Aluminum frames have rivnuts instead of welded-in bottle bosses to avoid heating the thin-wall section of the aluminum tubes. A rivnut has a weaker, unthreaded area just below its flange that bulges out as it is drawn up during installation

My guess is that the bolt will easily unscrew if the bolt is not rusted, and you can keep the rivnut from turning while you unscrew the bolt (counterclockwise). Squirt or spray some lube (penetrating oil, or WD-40, or any thin oil you have around) around the bolt, then wedge a small flat-head screwdriver in between the rivnut flange and the water bottle cage to keep it from spinning. If the bolt isn’t rusted and stuck to the rivnut, it should come out. Twist the screwdriver to maintain pressure between the rivnut and the bottle cage while unscrewing the bolt.

If the bolt won’t come out, just drill off the head of the bolt (wedging it as above) to get the cage off.

As for how to subsequently mount a bottle cage again next spring, you will need to replace, re-set, or glue in the rivnut.

If the bolt came out easily, and the rivnut threads are in good shape, you can re-set it in place with a rivnut installation tool.

Lacking a rivnut tool, you can reset the rivnut with a long M5 bolt and nut. Thread the nut far up onto the bolt. Screw the bolt into the rivnut until you are sure that it is sticking out the bottom end of it; otherwise, you will mangle the rivnut when drawing it up. Screw the nut down against the top of the rivnut. Hold the bolt head with one wrench and tighten the nut down against the face of the rivnut with another wrench. Keep tightening the nut until the rivnut has bulged enough inside the down tube so that it is secure and will not rotate.

Instead of resetting the rivnut, you can also superglue it in place. Superglue won’t stick to corrosion and oil, so repeatedly spray rubbing alcohol on it and spin the rivnut to flush out oil and corrosion. Cover painted areas surrounding the rivnut with tape so the superglue won’t attack it, and get glue in under the rivnut flange and around the hole as well as you can.

If the bolt was frozen to the rivnut so you had to drill the bolt head off to get the cage off, there should be enough bolt sticking out of the rivnut to either cut a screwdriver slot in it or grab it with vise grips. Then peel up the edges of the rivnut and grasp, or snip off the top of it and push it down through the hole into the down tube and rattle it out into the bottom bracket shell (after you remove the bottom bracket).

Getting a new rivnut of the same diameter with an M5 thread without having to buy a big quantity of them will be your next challenge. Try calling a local frame builder to not only get the rivnut, and, better yet, to have him or her remove the old one and install a new one.
― 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.

Follow @lennardzinn on Twitter.