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ASK RBA: ASK RC: AERODYNAMIC ADVANTAGES OF INTERNAL CABLE ROUTING
Richard Cunningham
February 22, 2010
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(Photo: Yuzuru Sunada)
I've been riding a few decades so I remember back in the early days of aero bikes when exposed cables were no big deal based on a wind tunnel study. (It got a lot of press at the time.) In that study, a bike with no cables at all had the same drag as one with fully exposed cable runs. Why then bother to run them internally?
Of course, nowadays, hiding cables in frame tubes, behind fork steerers, etc., is de rigeur for a TT bike, and even shows up on road bikes – Cervélo and Felt are two examples. So what changed everybody's mind? What did the guys who did the earlier study do wrong?
– John
Wow, you have touched upon a tender subject. As long as the cable housings are parallel with the air stream and riding in disturbed air (like they would be mid-way down the top tube or behind the fork on the down tube), there should be no significant drag penalty to route them outside the tubes. BUT, when you are spending all the time and effort in the wind tunnel and at the computer to make an Aero TT frame, why wouldn’t you clean up the cable routing? PLUS, who would buy a $12,000 TT bike with exposed cables if there was a sleeker looking option? That said, aerodynamic improvements are gained by making small changes on every part, so designers would not risk giving up a little drag to make cable routing easier. The old data was not wrong, but now that advanced carbon fiber molding techniques are available to all TT bike designers, greater reductions in drag have been achieved and thus a “relatively small” increase in drag back then represents a much greater loss today.
Contact Richard Cunningham for questions or comments, or just to talk bikes at: askRC@roadbikeaction.com
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