Hello Wrenchs:
Do you have a rule of thumb for cable housing length? One extreme for cable housing is that its so short you can’t turn the bars at all. The other extreme is to leave them so long that you can bring the bars all the way around till they contact the frame. Somewhere in between is probably an ideal, but where is that? Enough to move the bars 45 degrees? 30 degrees? 20? A simple rule of thumb like this could be really helpful to all of us who build out our own bikes.
Thanks in advance,
Jim
Okay, but that recommends the long extreme: The handlebars must be able to turn as far as they can in both directions without being limited by a cable pulling taut. Instead, the turning limit must be set by the handlebar bumping into the top tube or by the brake arm or reflector bracket bumping into the down tube.
Is that much cable really needed? So again I am asking the Wrenchs what they do for the bike of someone who is trying to minimize housing and therefore drag?
For a road bike I like to cut it so when the bars swing they are stopped just prior to the HB impacting the frame. For a TT bike as short as possible as long as I can turn with no issues.
Exactly, but what does that mean? If you go look at your tri bike right now, how far can you turn the bars before the cables stop the them?
Also: My question is only about tri/TT bikes.
all the way, but I am on a bayonet fork system 
and can push extra cable into frame if needed
.
There is really no absolute answer. Here’s some of what you’re weighing: Ideally, you want the cables as short as possible, for better aerodynamics, for lower weight, and for just better shift and braking action. However, you also want the housing and cables long enough to be able to turn easily while riding, my own turning guideline is to be able to easily do a 180 deg turn around a cone on a road at a very slow speed (slower than walking speed) and this requires substantial handlebar movement. So I would want my cables at least that long. Another thing to consider: If you’ll ever be putting the bike in a car, sometimes when you remove the front wheel, the handlebars will have be turned at least 90 deg to the frame to be able to lay down the bike or to put it in a narrow spot. So I like to have enough cable length to be able to do that as well.
In an attempt to improve aerodynamics I cut my rear brake cable too short so I can’t turn the bars right more than 45 degrees without it applying the brake. It doesn’t affect me during a race but it’s a pain in the ass when trying to make sharp right hand turns.
Of course, I’m too lazy to fix it. I just post here complaining about it instead.
On my bike, not very far. I estimate I can turn the HB about 30 degrees in either direction.
If you don’t cable the bike to allow absolute freedom of movement, then at some point the cables/housing will come under tension from turning the handlebars. They are not designed to limit such movement. It might not be an issue in a practical racing scenario, but I don’t think it’s good practice.
No hard rule but keep in mind that tight housing sweeps might actually create more cable friction than long ones. Keep the sweeps smooth, try to route the straightest line possible and stay aero. Or pick two.
Agreed with this. Road bike, enough that the housing stops the bars just before they impact the top tube. On road bikes you actually need to turn, generally.
Tri bike, as short as possible. No turning necessary
all the way, but I am on a bayonet fork system and can push extra cable into frame if needed
You shouldn’t be able to, as the housing goes thru tubes in the frame and there is nowhere for the housing to go but out the other end.