Monday, February 06, 2017

A Bit of Science, Mixed with a Dash of Crash

2017 has started off with an aggressive uptick in my training. Probably too aggressive, but I'm having fun. Or I was.

I spent almost all of 2016 on the road bikes. I logged over 5000 miles in the year, and probably 4600 of those were on the road. I chased every moving part on the Blue more than once, rode the Fuji 'til it got stolen, and then was back up & rolling a week later on a new Fuji commuter/back-up-race-bike.

But in the Fall I got a cross bike, and while it was more of a novelty last year, it's really become something of a new obsession this year.

When we took a family trip to MD last year, I took the cheaper road bike. This year I took the cross bike with two sets of wheels: one for road, one for dirt.

I've spent time chasing the setup on the thing, too, and I really got it to the point where I could do just about anything on it, for any amount of time, and just love the experience. I'd dropped from 2x11 to just a single 40T chainring, and the road wheels run an 11-28 cassette while the mud wheels run 11-32. All run through Shimano 105, and yes thankyouverymuch a short cage derailleur works just fine.

But while I was able to leverage my 2016 knowledge to set up the tire pressure on the road wheels, I found myself watching waaaaay too many Internet videos for the cross tires. The videos said most racers run around 30psi, and might dip as low as 25. But when I asked around, I heard what sounded like impossibly low pressures of 20 - 22psi. At that range, the rear tire appears to be flat when I get on...and I only weigh 140lbs.

I'd long theorized that most people can't actually tell what the "right" pressure is, and that outside of an extremely narrow window (maybe +/- 2psi), it's either simply too low or simply too high. This theory came from my experience in motorsports, where a .25psi change in tire pressure can result in a net suspension change of 25lb-in. Bearing in mind that a Miata goes from "compliant" to "rock-hard" with a 50lb-in suspension change, I decided to test my theory.

I started my test by just running the bike at a fixed pressure: 22psi front & rear. I did this not-very-scientifically for about the last month or so on a pair of Clement BOS tires mounted on Easton EA90XD road-tubeless wheels. I found the setup to be absolutely buttery smooth on cobbles and gravel, but any slight bump went straight into the rim. On dirt & grass, 22 seemed to offer fantastic traction, as well, so it seemed like a great setup.

But then I rode with some teammates who were on matched bikes, but clearly much higher pressures, as their rear tires looked rigid. I noticed they were far less cautious in picking their lines through roots & rocks than I, so I figured it might be worth some further experimentation.

A bit of research suggested I might consider a 45/55 front/rear air-pressure split, so I aired the front to 26psi and the rear to 28. It was horrible: wildly bumpy on cobblestones, the tires meandered through gravel, and worse yet: roots still went straight through to the rim. But on smooth surfaces, the low-rolling-resistance made me faster than ever.

Friday afternoon I split the difference and ran 24 front / 25 rear and tried again. Once again, the bike wanted to wander on gravel, but seemed far more planted on cobblestones, while still offering a fair amount of speed on pavement. I found the bike to be very controllable on hard-pack dirt, too, but before I could find any grass to test...

I crashed hard. I guess after 8000 miles I was overdue for a big one. I was coming out of a long smooth trail, eyes up and moving fast, when it felt like something just grabbed and stopped the back wheel. Not like a lock-up, but like it snagged on something. I had just enough time to register the increased resistance before I went flying.

I've played enough sports in my time to know not to stick my arms out, and while I don't know exactly how I landed, I know it was hard enough to bend my handlebars around and smack my head on the ground hard enough to give me a good headache. So I avoided the common wrist & collarbone injuries, but there may be a rib or two that's not quite what it used to be.

The good news is I was able to ride out and get back to my car. The bad news is I don't know exactly what pulled me off the bike, so I don't know how to avoid it next time. Well, that and the need for a new helmet & handlebar. And possibly some ribs. But other than that...

So now I'm on a mandatory rest day off the bike. I rode yesterday outside to see my general condition, and while I felt ok then, I do not feel ok today. Racing season starts in 2 weeks. Yay timing.

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