Marginal Gains via Bike Components?
I sat on my patio bored and beat in the sun staring at my bike thinking about how to kill time. I thought to myself that it's probably time to throw on a new chain and maybe lose the 11-25 cassette now that I'm not riding much, I'm back in the pool, and my knees are starting to develop a twinge indicative of pushing perhaps too big of a gear. I threw on Shimano's newly designed 11-27 cassette and before I threw on the chain I spun the ceramic bearing equipped pulleys on my Red derailleur and noticed how badly they moved. I ignored this for now and installed a 6700 Ultegra chain (only after obsessively comparing it's length to my discarded chain). After I scoped out SRAM's website for some insight on my gunky bearings and found this:
Attention Red: the ceramic pulley bearings require regular maintenance. Re-grease bearings using SKF LGHP2 grease after 100hrs of use in dry conditions or immediately following any significant exposure to water (riding in heavy rain, water crossings).
I thought aloud, "100 hours?! Are you kidding me?". I remembered that somewhere in my tool box hid a syringe full of blue grease (pictured) that came with my Red Group. It seemed like something close enough to the google results for the aforementioned "SKF LGHP2", but the question still remained, why do sealed cartridge ceramic bearings need overhauling on such short intervals compared to a standard bearing? A tech document a few years ago from Campy stated that ceramic bearings have such smooth surfaces that they push the grease out of bearings, rather than retaining it. I wasn't completely convinced by this and it seemed more like marketing for their CULT bearings (which are nice in their defense).
When you think about it, these pulleys contain the fastest spinning bearings on the bike. If you turn the cranks at 100 rpm, the pulleys are at 481 rpm in the big ring and 355 rpm in the little ring. Thus the more the bearings spin the more potential to suck up watts. On the other hand derailleur pulleys seem to have much less radial load than bottom bracket and wheel bearings and this load contributes to bearing drag. I temporarily removed my gloves and apron and went back inside to get on www.analyticcycling.com to try to get an idea of how much these pulleys can actually affect power. There I found a calculator that outputs speed based on the input of power (250 watts was the default). The system assumed a combined 75kg rider and bike weight on a typical flat asphalt road. The 75kg combo @ 250 watts travels 11.23 meters per second and will travel a distance of 40.428 kilometers in one hour. The second time around I inputed 250.5 watts, The .5 watts comes from the proven advantage of a ceramic pulley bearing versus a Dura-Ace pulley bearing (surfing the web for 10 mins). The 250.5 watt outputted 11.24 meters per second with the same variables. This equals 40.464 kilometers in one hour. This watt difference results in a 36 meter advantage, which is you've read any of our 40k time trial articles is a HUGE difference that can win or lose a race.
In the end I wont be overhauling my pulley bearings every 100 hours, but I definitely will consider doing it at least twice a year.