Yaw know what I mean?

Canadian Cycling Magazine - - FEATURE -

The new cy­clist checks out a new pair of aero wheels. Let’s say it’s the Dura-ace R9170 C60 hoops for disc brakes. They fea­ture the D2 rim shape, which Shi­mano says re­duces air drag bet­ter than other aero-shape rims at yaw an­gles from zero to 15 de­grees. “Zero to 15 de­grees?” the rider might say. “That doesn’t sound like very much. What if I was head­ing north and a wind was com­ing right out of the northeast? That air would hit me 45 de­grees. Those wheels don’t seem able to han­dle that.”

If you know your physics, you’ll catch the new­bie’s mis­take: equat­ing yaw with wind di­rec­tion. “Yaw is the vec­tor sum of your for­ward speed and the wind an­gle,” says An­drew Buck­rell, ceo of Stac Per­for­mance. He knows about wind and its ef­fects on a rider and gear. His com­pany has de­vel­oped a method of scan­ning a rider and his rid­ing po­si­tions. This in­for­ma­tion can then be put in Stac’s vir­tual wind tun­nel to see how the rider can get more aero­dy­namic.

“A 45-de­gree yaw is gen­er­ally un­re­al­is­tic,” Buck­rell says. “In fact, the faster you are, the less yaw you ex­pe­ri­ence. Take an ex­treme ex­am­ple: if you were trav­el­ling in an air­craft at 800 km/h with a 10 km/h sidewind, the yaw an­gle will be roughly zero de­grees. For a cy­clist, it would take a huge cross­wind to get a yaw above 20 de­grees.” Since speed af­fects the yaw, then a slower rider, Buck­rell says, should look for wheels that work at a broad yaw range. If you are a faster rider, then wheels that per­form well in a nar­row range of yaw would suit you bet­ter.

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