Thursday, December 15, 2016

Review: A Twist of the Wrist II

A Twist of the Wrist II was recommended to me by Pengtoh as being one of the best books about bike handling. While I've never actually ridden a motorcycle, my understanding is that as 2 wheeled vehicles that move at high speed, some of the skills and thinking involved might be transferable to the lighter, more environmentally friendly vehicles.

To my disappointment, the first third of the book is all about throttle control. Motorcycles (and bicycles) are designed to handle best with a 40/60 weight ratio (40% of the weight on the front, 60% on the rear). When you corner a motorcycle you tend to have a 50/50 weight balance. How do you get the ideal 40/60 weight balance? You apply a constant 0.1g thrust at the throttle. That means that all through the corner you need to be accelerating (he calls this roll-on) throughout the entire process. This sounds scary but I guess if you're going to be racing a motorcycle the answer seems to be: "More gas! What was the question?" This has zero applicability to bicycles: not only is pedaling through corners difficult (you risk pedal strike if you have a low BB), but you just don't have the power to apply a constant 0.1g acceleration through any corners!

The second third of the book is more applicable to cycling. It's about relaxing. Basically, the barrier to high performance on 2-wheeled vehicles is what Keith Code calls SR (Survival Reflex). If your SR is triggered you will slow down. Worse, if your SR is counter to what the bike needs to be doing, you'll crash. The key to not triggering your SR is to relax. Most of the advice here is very relevant: keep a bend in your elbows, unweigh the seat, and don't keep a death grip on the handlebars! In particular, when you encounter road chatter, a frequent reaction is to tighten up on the handlebars. Don't do that! Keith Code notes that by tightening your grip on the bars, any oscillation will now get transmitted throughout the entire system through your body, which is a bad bad thing to have happen. Good stuff. He provides practical tips on how to get better --- including slowing down before you approach a corner, and then slowly speeding up your corner entries as you get more comfortable. A few things aren't applicable: for instance, a motorcyclist can lean all the way over to the point where his knee touches the ground. Bicyclists can't do that --- the tires will lose traction long before that. Furthermore, a motorcycle is so big and heavy that counter-steering is the only way to quickly change the lean, while bicycles (with the exception of tandems) can generally be steered without counter-steering, though Code points out that if you do counter-steer you can start the steering action later, which lets you get through the corner by leaning less at greater speed! Good stuff, and worth a refresher read even if you're a decent bike handler.

The last third of the book is about avoiding the tunnel vision that tends to happen when you start exceeding your comfort zone. He talks about picking a point far enough ahead that you still have sufficient situation awareness to know what's going on. Similarly, for cornering he recommends first look at the place where you've picked to turn the bike, and then just before you get there to look through the turn so you steer the bike there. He also recommends that every corner should have only one steering action, and if you second guess yourself in the middle you'll slow down. Again, useful advice, and worth a read.

Obviously, you can't learn to ride a bicycle at high speed by reading a book. But assuming you've had a few mountain descents under your belt, some of the counter-intuitive things Keith Code mentions are worth practicing. Some of the advice (like tuning suspension) isn't applicable to most road bikes, but hey, anything with two wheels simply doesn't behave like a car, so in general it's worth seeking out people who've spent a lot of time thinking (and practicing) bike handling.

The oddest thing in the book is the glossaries at the end of each chapter. They cover elementary terms (such as the phrase "vice-versa") that makes me wonder about the vocabulary limitations of motorcycle racers.

The book doesn't cover any low speed bike handling problems (which motorcycle road racers never encounter but mountain bikers do), so don't expect any special insight there.

Otherwise, the book's worth a read. It doesn't make me want to ride a motorcycle, but does give me some sympathy as to the problems a motorcycle road racer would encounter.
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