Technical Q and A with Lennard Zinn: On bearings and brakes

By Lennard Zinn

Dear Lennard,
I want to replace the Raceface X-type road bottom bracket on my Giant TCR C1 road bike.

I want to replace it with one that is smoother running, likely one with ceramic bearings. Will any Shimano compatible ceramic bearing bottom bracket work?

I guess this sounds like a very general question, but it is probably because
I have never changed or installed a bottom bracket before. I didn’t know if I would have to worry about spacers to keep the proper chain line, etc.
Darrin

Dear Darrin,
Shimano Hollowtech II, FSA MegaExo, and the drive-side cup of TruVativ/SRAM GXP are all interchangeable with RaceFace X-Type cups.

As for doing the work, I of course think you ought to just get my book or DVD and use it to work on your bottom bracket and the rest of your bike. You will be amazed at how easy it is to perform the task you’re asking about. Here is how you upgrade the bearings in your RaceFace X-Type bottom bracket with ceramic bearings:
Lennard

Dear Lennard,
I’ll be taking delivery of a pair of Shimano WH-7850SL wheels shortly, and for no good reason in particular, I want to replace the stock bearings with ceramics. Beyond the fact that no one seems to be able to give me a definitive answer as to how many ball bearings these wheels require, I am mulling over the issue of retainers vs. loose balls. The engineering drawings and parts list for these wheels imply 22 loose 3/16 on the rear drive side, and a retainer with an unknown quantity opposite, and two retainers of 5/32 in the front.

Should I “refill” the existing retainers (where they are used), or use loose balls entirely? In the 70′s, back when I co-owned a bike shop in San Francisco, we always, always replaced retainers with loose balls – hence more of them, better load support, longer wear, etc. Comments I find on various bearing mfg. websites and elsewhere, seem to support the improved wear contention of loose balls, but also imply perhaps greater friction (or not). Do you have an opinion? While I’m at it, is there a preferred lubricant for a hybrid steel race/ceramic ball application? Is there any reason to go beyond a grade 5 ball?
Michael

Dear Michael,
While you are correct about distributing the load over more balls, you want the retainers for reduced friction, because bearing retainers separate the balls from each other. This reduces friction by preventing neighboring balls, whose adjacent sides are turning in opposite directions, from rubbing on each other.

Although you can use any grease you wish in the bearing, it will run faster, in the hand at least, with lighter, less sticky greases. Rock ‘N’ Roll Super Web grease works well in loose-ball cup-and-cone bearings as well. I also like Slick Honey or Shimano’s fluorescent green grease for this; bearing companies and lube companies offer alternatives as well.

Finally, no, I can see no reason to go beyond a Grade 5 ball.
Lennard

Dear Lennard,
Seeing that I don’t do many time trial events per year, and the fact that I am pushing 210 pounds, I have foregone a TT rig for just a set of TT bars that I mount on my regular racing bike. I figure that unless I can punch a hole the size of Levi, why spend a bunch to save a quarter of a percent on aerodynamics.

However, a month ago I upgraded to a bike that came with an Easton EC70 oversized carbon handlebar and now that my favorite TT (Colorado’s own KMHTT) is here, my shop tells me I can’t use my Profile T2 bars with a carbon handlebar.

Is this true, or can I some how make it work?
Jess

Dear Jess,
The Easton EC70 oversized carbon handlebar is compatible with an aero clip-on bar.
Lennard

Regarding last week’s column on road disc brakes:

Dear Lennard,
Two things on road bike disc brakes. On running smaller discs, and the problem of heat: Yes, the greater speeds will generate more heat in the discs. BUT they will also be exposed to higher airflow than MTB brakes, offsetting the heat with better cooling. DH rotors are not oversized merely for stopping power; it is to create more heat dissipation at the lower speeds you experience in steep, technical terrain. This is offset by increased airflow, as seen on road bikes.

On carbon/carbon brakes on bikes: It quite simply it will not work. Carbon brakes are designed to (and in fact MUST) run at much higher temps than steel rotors. If you’ve ever watched an F1 race, you will notice how often the rotors glow red under hard braking. A bicycle simply cannot generate enough heat into the brakes quickly enough to bring them up to a temperature at which they will work consistently. Imagine waiting 5-10 seconds after you pull on the lever for your brakes to start working.

That is one reason for parade laps in motor racing; it gives drivers the opportunity to bring tires and brakes up to operating temps.
S

Dear Lennard,
I don’t think carbon/carbon brakes will work on road bikes.

On race cars, they work – once you’ve gotten them hot. The “warm-up” lap these days has as much to do with putting heat into the brakes as into the tires (the tires have warmers on them while in the pits; the brakes do not). Even then, braking at the first corner on any Formula 1 race is very dicey. Auto race brakes work well at insanely high temperatures – watch any 24-hour race and you can see the discs glowing red at night.

On a road bike, the disc and caliper would be exposed to fast-flowing cooling air. (In cars, the discs are enclosed in a shroud, inside the wheel – designed to maintain a constant brake temperature). Sudden emergency braking on a road bike would be much worse than it is with rim brakes today – initially there would be close to zero stopping power. Sure, on a long high-speed descent, you’d eventually get stopping power – but those descents don’t come up in races very often.
Paul

Dear Lennard,
Regarding the carbon-carbon brakes, I was previously an automotive engineer and had some experience with carbon brake pads on carbon-carbon rotors. Typically the coefficient of friction increases dramatically with temperature to the point where the rotors glow red-hot.
The biggest challenge has been achieving high enough brake temperatures, however this is with vehicles, which require a much higher braking capacity. I think bicycles will be able to get away with an almost paper-thin carbon rotor that can operate effectively at relatively low temperatures. If the concept could be developed, it could allow rim weights to significantly decrease while increasing brake capacity.
Richard

Dear Lennard,
I currently ride a flat bar road bike with hydraulic disc brakes for my commuter bike. The stopping power in all conditions, especially in traffic easily compensates for the weight penalty.

The only issue I have is that the cumulative effect of having a 10sp cassette on one side and the disc rotor on the other leaves little width for spokes on the rear wheel. The wheel is prone to deflection due to the shallow angle of the spokes (the rough Sydney roads and the load in a pannier don’t necessarily help either).

For disc brakes to really be the “next big thing” I would suggest that the standard for the axle length of road bikes be increased to allow greater room for the brake rotor, a 10sp cassette, and leaving enough room to allow the spokes to adequately support the rear wheel.
Richard

Lennard,
You quoted this rule in your latest column:

1.3.025 - Freewheels, multiple gears and brakes are not permitted for use on the track during competition or training.

Disc brakes are forbidden in cyclo-cross training and competition.

What in the world does it mean to forbid disc brakes during training? If Ryan Trebon goes on a mountain bike ride, and does a cyclocross dismount to hop a log, does that count as “cyclo-cross training”?

What is the penalty? Same thing for the track? If the guys at the velodrome don’t mind (they probably do, but let’s pretend), why does the UCI care if I ride my 30-speed road bike around the track for 10 minutes? This is just weird…
Rob

It should be mentioned that Campagnolo, much to their credit, offers “alternative” freehub bodies for their hubs and wheels that will accept ‘brand x’ cogsets (both SRAM and Shimano).
Peter