Technical FAQ: Road discs and bottom brackets

This week, Lennard Zinn addresses questions about road disc brake options and a follow-up regarding creaky bottom brackets.

Rim brakes with disc-brake wheels?

Dear Lennard,
I have a 2012 Cervelo S5 and a Felt B2 Tri bike. I have scrimped and saved enough to get a new pair of wheels that I want, the new 404 NSWs (I run Clinchers). I do plan on getting a new bike in the next few years and would like these wheels to be part of the new system. When I was looking to buy the wheels, I was asked if I use disc brakes. Can I get a disc-ready wheel to use with my old calipers and convert the wheels to disc when I get a new bike with disc brakes, or do I need to stay with caliper wheels with my old caliper bike? I can’t afford to buy two sets of wheels and I am trying to be smart about the purchase.

— David

Dear David,
The short answer is no. There are lots of reasons for this.

1. The rear hub spacing is different. The “axle overlock dimension” from the face of one axle end cap to that of the other is 130mm on a rim-brake wheel and 135mm on a disc-brake quick release (QR) wheel. You would have to pry apart your dropouts on your rim-brake bikes to fit a disc-brake wheel. And that is with a QR disc wheel, which are going away; see the next item.

2. If you wait a couple of years and buy a disc-brake bike, it will almost certainly have thru-axles front and rear, not QR skewers. So, not only would the hub spacing be different from the current 135mm for a QR disc-brake wheel (142mm X 12mm is the current road thru-axle spec), but the attachment system will be completely different as well. Even if the length difference did not exist, the wheels would not be interchangeable.

3. The rims for disc-brake wheels are not designed to handle rim brakes. For carbon clincher rims to not overheat during rim braking to the point that the resin holding the carbon matrix together softens, the rim needs to have a resin with a super-high melting point. While disc rims may use such a resin with a high Tg (glass-transition temperature), they do not have to since they need not be designed to withstand heat from braking. So, if you apply a rim brake hard at high speed to a disc-brake rim, you just might experience having the rim walls fold out flat like a limp taco shell, exploding your tire. Furthermore, many disc-brake rims have decals and topography from the mold that would interfere with rim brakes.

If you want wheels now and a new bike years down the road, just get the 404 NSW wheels you were planning on and not the disc equivalent, namely the 404 Firecrest Disc.
― Lennard

Hydro brake levers on an aero bar

Dear Lennard,
I have a bike with hydro disc brakes and an aero bar. I would like to have at least one brake in hand when I’m riding in the aero position. Is there a way to control a single hydraulic brake from two different levers, one on the aero bar and one on the base bar?
— Jim

Dear Jim,
I know of none currently available, nor of any in the works. However, if you want to switch out your hydraulic disc brakes for mechanical disc brakes, you will probably be able to get a two-lever system to operate each brake next spring from TRP.

This is what TRP USA’s managing director Lance Larrabee says about it:

“We don’t have a two-lever to one-caliper system, but we do have one-lever to two-caliper hydraulic brakes. We are working on a new mechanical system for two levers to one brake aimed at kids and the city market; that could be adapted to performance bikes. That option should be announced to the public in spring 2018.”

― Lennard

Feedback on Campagnolo press-fit bottom brackets

Dear Lennard,
In response to the reader having problems with a Campagnolo Chorus UT crank and a press-fit BB: I, as well as numerous other riders, have had the same problem. There was a lot of creaking and I could visibly see the crank moving under load. Frankly, it was driving me insane to the point where I didn’t know if I should throw out my Campy Record 11 crank or the top-of-the-line carbon frame.

I tried epoxy — several types of very expensive epoxy, actually. But needless to say, no epoxy was able to withstand the pedaling forces in a joint between the BB shell and UT-crank, which is inherently wrong.

Fortunately, I heard of a small Belgian company called C-Bear. After installing one of their BB shells, the problem was solved. In five years, I have not heard a creak.

What I did was press two (non-threaded) sleeves into the OSBB of my Specialized S-Works frame. These are then held in place by two normal, threaded Ultra-Torque (aluminum) cups.

You can see the product here.

As you can see from some of the pictures on the C-Bear homepage, the Lotto-Soudal team used C-Bear bottom bracket inserts in its Ridley press-fit bottom brackets with Campagnolo cranks. I also believe Astana did the same when they were combining S-Works frames with Campagnolo cranks.

In my opinion, the combination of (most) press-fit BBs and Campagnolo cranks/BB is inherently unstable, since the UT bearing is by definition sitting outside the frame. This is different than, for instance, a SRAM press-fit BB, where the bearings are sitting inside the frame. In fact, I have two bikes running like this without problems.
— Henrik