Technical FAQ: Tire width – rim fit, bottom brackets and silencing disc brakes

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

Dear Lennard,
Assuming that my road bike frame has clearance, what is the widest tire that I can install in my current wheel? My current wheel is a 2011 (year) Mavic Ksyrium SL. The width of the wheel is 15 mm, measured on the inside from the interior end of each hook.

I currently have 700 X 23mm and would like to go to 700 X 25 tires.

The reasons for me wanting to move to a 700 X 25 are: To have a more comfortable ride and to have more stability, especially when going downhill on steep roads. Is my thought process making sense? Do you recommend me to move to 700 X 25 or should I stay with the 700 X 23?
— Omar

Dear Omar,
Yes, you can use that combination of a 25mm-wide tire on a hook-bead (crochet) rim with a 15mm inner width. ETRTO (European Tire and Rim Technical Organization) sets standards for what tire can be used safely with what rim and at what maximum pressure to preclude blowing it off of the rim. Based on ETRTO standards, the widest tire you can use on that rim is a 32mm, with a max pressure of 7.85 bar (114psi).

Yes, your thought process makes sense. Using a 25mm tire on that rim would not only provide more comfort and traction, but it would also reduce rolling resistance and increase resistance to pinch flats. The only downside is added weight, which, in my opinion, pales in the face of faster rolling, more comfort, better handling, and fewer flats.

Mavic has a nice discussion of rim width as it relates to tire width and includes the ETRTO (standardized widths) chart.
― Lennard

Dear Lennard,
Perhaps the most significant change to new bikes seen at my LBS is the ubiquitous metal bottom bracket sleeve or cup system that replaces press-fit systems of the past. For 2020 models Trek has begun putting in T47 in some models and I’ve also seen other systems like Cervelo’s BB Right. When I researched this, I came to understand that these systems are increasingly being put in mass-produced carbon frames as a means of reducing customer complaints of creaky bottom brackets, but also as a means of reducing manufacturing costs in that they do not require such tight tolerances for alignment and roundness of the holes, thereby reducing frame rejects and QC testing costs. I can understand that, which comes to my question of what the best threaded BB system will be.

Some manufacturers (e.g. open mold producers) are still shipping frames with BSA threads, while the major brands are using T47. I see the latter as having three major benefits, namely a larger aperture (to accommodate a 30 mm spindle and larger bearings), the possibility of setting the bearings within the frame as opposed to being outboard in cups, and allowing for different BB widths, (as opposed to being limited to 68mm). In light of these considerations and as a frame builder, do you intend to make T47 the default for custom metal frames? Or is this something that is more relevant to carbon frames? Do you think T47, which is also an open standard, will ultimately replace BSA?
Marc

Dear Marc,
You are correct about a lot of the advantages of T47 threaded bottom brackets. I believe it to be a great improvement over threadless bottom bracket shells. I use T47 on my clydesdale stock-sized big bikes for many of the reasons you cite.

On custom Zinn titanium and steel frames, we offer both T47 and BSA. BSA is still on the majority of them, and I see no reason to eliminate BSA. Those bikes almost always get our own CNC-made cranks, which have 24mm spindles, which work fine in BSA shells. Creaking is not an issue, thanks to the threads and the metal construction. While BSA won’t work with a BB30 crank, it will still work with the longer 30mm spindle on a BB386 EVO crank, with external bearings.

For these reasons, I don’t am not predicting the imminent disappearance of BSA. T47 will continue to gain market share, which is great. If it does completely replace BSA, so be it.

With threadless bottom bracket shells, creaking can be reduced with thread-together bottom brackets.
― Lennard

Dear Lennard,
Just a few months ago my wife and I each got a new Trek Madone SLR7 with an Ultegra R8000 Di2 group with hydro brakes.

Although her first few rides were silent, soon after 500km the rear brake started to squeal. I several times cleaned the rotor with alcohol and lightly sanded down the resin pads. This did not work. The rear brake would squeal after just 50km of riding after each cleaning.

So, I bought a new set of L03A resin pads (despite the “old” pads having barely 500km of total use), performed the ritualized bed-in process, and this definitely solved the squealing problem. But not for long—the rear brake started shrieking again after another 50km.

I’ve recentered the caliper once already. But this, too, did not silence the rear brake.

I’ve the same bike/component setup, although a different size bike, and my ride is whisper quiet.

What gives?
— Greg

Dear Greg,
Sounds like you have done all of the right things. You didn’t say that you sanded the pads face-down on drywall-sanding screen, which allows anything that comes off of the pads to fall down through the screen, rather than being rubbed across the pad face. If you didn’t do that, you might try it.

If contamination of the rotor or pads can be eliminated, and assuming you have checked that all of the caliper bolts and rotor bolts are tight, then the squeal is likely due to vibration. Sometimes there’s just a harmonic in the frame that gets set up when the brake is applied. Your bike is quiet, and its different size frame would have a different resonant frequency that braking doesn’t sync with.

You could experiment with things to change or damp the vibration. The first thing to try would be significantly different pads to see if that changes it. Try sintered metallic pads; they often have a lower coefficient of friction and may change the vibration. The fact that her brake doesn’t squeal right away with new resin pads indicates that the vibration may be sensitive to small changes in the pad/rotor friction relationship, so changing the pad type might be enough to eliminate the problem.

With metal frames, we sometimes need to do something like weld in a strut to change that frequency, and the problem is solved. Not so easy with a carbon frame. If sintered pads don’t fix it, you could try damping the vibration by sticking something thick and damping to the stay, maybe like a long strip of thick Shelter tape, or maybe even taping a rubber strip or dowel stick to the stay.
― 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.