What the Cog?

It used to be that the big gears on a bike were up front and the little gears were in the back. This has all been turned upside down now. Bikes went from two chain rings to triples, back to doubles, and now 1-by drive trains seem to be the norm in the MTB world. Funny how the pendulum swings like that. And people just gotta have that latest setup too. I think 1-by drivetrains are stupid.

I ride a variety of terrain - uphill, downhill, dirt roads, pavement. A mountain bike works on all of it. My Santa Cruz Tallboy has a 2x10 drivetrain, meaning a small and large ring up front with complement of 10 cogs in the back. I use all of those gears regularly. I could use more gear on both low and high ends, actually.

Sometimes on the road, I spin out with a tailwind or heading downhill. A bigger ring up front would be nice, like a triple. But then on the other end, I could use an easier gear or two for some climbs. If a double crank is not enough, how could a single ring drivetrain possibly be enough. Yeah, the mocho types say just grow a pair and tough it out. How about join me on a 5000ft climb to 13,000ft in Colorado with your 1-by?

The predecessor to my Tallboy was 26" wheeled with a triple crank. The 22:34 ratio gave me a 16.8" gear. Then 29ers came around, and the industry graciously gave us a 36t cog to ease the burden of turning that wagon wheel. But they also took away the triple. The new ratio of 24:36 with the bigger wheel pushed gear up to 19.6", a 17% jump! That is almost two gears harder on the low end. Two hour long climbs at 3mph already hurt. I didn't need them to hurt 17% harder.

So now new frames are being produced that are not even compatible with front derailleurs. This will limit selection of future frame purchases for me. Again, to mitigate some of the impact of loss of range, the industry now provides 42t cogs! Cogs have now become bigger than rings on most mountain bikes.

New 42t cog on left to supplement a 36t cassette with BIG ring on right.

When I mate a 42t cog to my 24t ring from my double crank, I get a 16.6" gear, pretty much right back to where I was with a triple crank on a 26" wheeled bike. Nothing I regularly ride around here requires such a low gear ratio. Only a ski area service road or two I infrequently hit might benefit.

Several companies now offer conversion kits. I went with One Up. Basically, you start with a standard 36t, 10spd cassette. The largest cogs are all bonded to an aluminum carrier. So you first slide on the 42t cog, then the cassette, but leave off the 15t or 17t ring to keep cog count at 10. Rather than have a big gap from 19 to 15 or 17 to 13, the kit includes a 16t cog, so you remove 17t and 15t cogs and add the 16t. This way the steps are 19-16-13. Still biggish steps, but not huge.

I head to Colorado for two weeks in September. There are several climbs out there that will see heavy 42t cog usage. Carson Rd up to highest point on the Colorado Trail, Black Bear Pass in Telluride, Maybe Gunsight Pass in Crested Butte are all motivation for lower gearing. Amount of hike-a-bike will be reduced and the legs will be fresher to ride again the next day.

The Tallboy will be going with me. It had developed a nasty bottom-bracket area squeak the last couple rides. Pulling things apart, the BB itself was buttery smooth. No delamination of alloy inserts in carbon frame either. I next moved to the VPP (Virtual Pivot Point) bearings. Pulled the assembly apart and found the bearings trashed.

I was not surprised, I had logged over 8100 miles on this bike so far and these were still the original bearings. I have never even ridden a third this many miles with my other full-squish bikes bikes without having to replace bearings or bushings. The Enduro Max bearings and grease fittings on the pivot link are key to the longevity of these bearings.

I already had the bearings on hand, as I had just replaced the upper rocker bearings because they were developing some play, which bugged me. The VPP bearings were so gone they fell apart when I tried to press them out, making it a heat and punch operation for removal. What a PIA. New ones went in fine, but the outer rubber seals that are not part of the bearings were trashed.

Hunting online, these could not be found anywhere, including Enduro Fork Seals, where I bought the bearing kit. So I emailed Santa Cruz service department inquiring where I might find them, as their online store didn't have them either. I got a quick response saying four were in the mail to me. How awesome is that?