Internal vs external cable routing - how aero?

[cjw66]

Hey, all--

I'm in the market to upgrade my aluminum TT/Tri bike to a full carbon frame. I'm currently riding the entry level Cevelo Dual which has worked well for me on short-course races but it's a bit heavy (20+ lbs w/full Dura Ace) and the ride is pretty harsh espeically on longer (40-50+) rides now that I'm training for a 70.3. I'd like to get the light weight and stiffness carbon can provide along with the more comfortable ride. I've got my eye on what looks to be a pretty decent full carbon TT frame but it has external cable routing (the Cervelo has internal).

My question is this: Does having thin cables running the length of the top and down tubes really affect the aerodynamic properties of the bike all that much? Keep in mind here that I'm a 40+ age-grouper who averages around 22mph on my bike legs in Olympic/International distance races so I'm not Norman Stadler averaging 26mph. So much of bike marketing is hype and jargon and I'm just trying to get a realistic sense of whether external cables really has any signficant impact on how areo the bike is.

Thoughts and suggestions are appreciated.

Thanks!
-Chris

 

[531Aussie]

It says here that internal cables cut about 1 to 2 watts of drag. If you Google the topic, I reckon you'll find similar numbers.

http://www.bikeradar.com/news/article/in-the-pits-time-trial-bikes-in-california-14601?img=7

That's obviously very small, but I guess you can calculate whether or not it's worthwhile in a time trial.

I suspect this isn't the best way to measure drag, but, according to this calculator, going from 400w to 402w (with all the other factors "factory set") increases speed from 42.02 kph to 42.10 kph

http://bikecalculator.com/veloMetricNum.html

 

[cjw66]

It says here that internal cables cut about 1 to 2 watts of drag. If you Google the topic, I reckon you'll find similar numbers.

http://www.bikeradar.com/news/article/in-the-pits-time-trial-bikes-in-california-14601?img=7

That's obviously very small, but I guess you can calculate whether or not it's worthwhile in a time trial.

I suspect this isn't the best way to measure drag, but, according to this calculator, going from 400w to 402w (with all the other factors "factory set") increases speed from 42.02 kph to 42.10 kph

http://bikecalculator.com/veloMetricNum.html

Interesting stuff. Given that I'm going to be averaging even slower speeds in the longer races I'll probably be happy to trade a tenth of kph for a more comfortable ride for my aging body. Thanks!

 

[Peter@vecchios]

It says here that internal cables cut about 1 to 2 watts of drag. If you Google the topic, I reckon you'll find similar numbers.

http://www.bikeradar.com/news/article/in-the-pits-time-trial-bikes-in-california-14601?img=7

That's obviously very small, but I guess you can calculate whether or not it's worthwhile in a time trial.

I suspect this isn't the best way to measure drag, but, according to this calculator, going from 400w to 402w (with all the other factors "factory set") increases speed from 42.02 kph to 42.10 kph

http://bikecalculator.com/veloMetricNum.html

Too bad rider performance, power out, etc isn't factory set, why so many of these calculations are fuzzy at best. BUT hard to measure performance on a bike so measure measureable things like the bike, but when you put a body on it, most are kinda lost in the noise.