First time building a bike from the frame up. I am confused on how I should route the shift and brake cables.

This is the Seaboard/Tsunami CX03 gravel bike frame. It is made of chromoly steel.

There are 2 internal cable slots on the downtube, and one external cable hanger.

I am using the Shimano 105 R7000 groupset and mechanical disc brakes. Until GRX comes out with crankarms that are 160mm or smaller, I will have to use the 105 crankarm. This is why I am sticking to having a front derailleur. When most people build on this or similar frames, they use a 1x drivetrain, so I am unsure where to put the front derailleur cable.

My cables are the Jagwire 2X Sport Shift Gear Cable Kit and the Jagwire Pro Road Brake Cable Kit. I just tried opening the Pro Road Brake kit, and there is only one cable. I am questioning whether I will have enough for both front and rear brakes.

How should I go about this? I would like Left brifter to be rear brake and Right brifter to be front brake (I apologize if this is not the standard layout!). So I was thinking to have the Right brake cable cross in front the headset and down the fork to the disc brake.

In the picture above, I labeled 5 positions. After that, do I put the Right shift (rear derailleur) cable in #1 or in #2? Do I put the Left shift (front derailleur) cable in the other slot, and hang the rear brake cable on #3, or the other way around? If I do hang the rear brake cable on #3, do I wrap it under the BB (and induce rubbing) or hang it over the top of the BB to reach the brake?

All advice on how to route the cables would be highly appreciated! Thank you!!

Right/Rear derailleur is 1-1-4
Front derailleur is 2-2-5
Rear Brake from Left brake lever is all the #3 clamps but you may want to play around with which side of the headtube to run it. I would guess running it around the front of the headtube and down the right side will work best but can't say for sure and you would want to rotate the top 1 or 2 #3 downtube clamps 180 degrees to route the cable to the right but leave the clamp near the bottom bracket as is.

For me, to be sure, rear brake on the left hand for road bikes too. Just like my motorcycle days, and all throttled wheelers...

Thanks for the reply! Do I not need to cross the derailleur cables in front of the headset, for example, Right/RD 2-2-4 and Left/FD 1-1-5? Or maybe even 2-1-4 and 1-2-5, somehow crossing the cables/sleeves inside the down tube?
Your suggestion of 1-1-4 and 2-2-5 is much neater, but I worry that the shift cables will have too steep a bend near the headset.

Unless athanasis is used to left hand braking, the more traditional use of the no. 3 clamps would be for the right hand brake. Right/rear is much more common and there are lots of bikes that run the cable along the left side of the bike to a brake. I don’t usually take pictures of the left side but I happen to have this tandem picture. The rear brake cable runs along the same line as anthanasis’ bike on the left side but is connected to the right lever.

You appear to be running a mechanical disc. Your bike is set up for external routing of the brakes (clamps #3). That’s a plus if you want to run hydraulic. Personally, I hate internal routing because it is around royal pain to work on and hydraulic internal is particularly difficult…you have to cut the hose to change the brakes. But kudos to your frame building for the external brake routing. You will need to run housing for the entire run, however.

For the shift cables, first I would check if the routing in the downtube has guides for the cable the whole way or not. If not, I would have the right cable cross over to port 2 on the non-drive side, then exit out the drive side. The left cable would go into port 1 on the drive side, and exit out the non-drive side. This will get you the lowest possible resistance. If the frame has internal guides that prevent this, then you will have to do right shifter to port 1, and have it exit on the same side. If there are no internal guides, an internal routing tool and a flashlight will help reduce headaches. The Jagwire Pro internal routing tool is fantastic.

With the rear brake, it looks like those guides can be flipped around. For setting up left lever controlling the rear brake, I would flip around the upper downtube guide to face towards the drive side, have the cable cross over the headtube to that guide. The middle guide could face either direction, I suspect facing towards the drive side would be better, but it would be worth trying both options to see if one works better. The lowest downtube cable guide looks like it might be low enough that routing the housing underneath the bottom bracket would offer less resistance, but again, mocking up both options to see what will work better is worthwhile. If the housing goes underneath the bottom bracket, it seems like the chainstay guide could go up or down, pick whichever offers the smoothest transition to the caliper. Adding a zip tie around the chainstay between the bottom bracket and the brace can help tidy up the cable a bit more, reducing the chance of it rubbing against the tire.

If you know the bike is going to be a perfect fit with the parts you have, you want to cut the housing to a length that allows for nice graceful curves, lets you turn the handlebar all the way to the left and to the right without binding up, and is otherwise as short as possible. If you don't know that it is a perfect fit with the cockpit you have, then add an extra inch or two to all pieces of housing coming from the bars so you have some room to change up handlebars and stem without having to redo all your cables. Either way, get your bars, stem, and levers positioned exactly where you want them before deciding on the length of the housing.

OP mentioned he wants to run left brake to the rear in post #1

I would first try running the shift cables on the same side as the shifters which works fine for most but sometimes "cross cabling" (where you run each cable around the headtube and into the opposite downtube holes but exits the correct side at the bottom holes) works better and is fine to do. Do what is the cleanest and least path of resistance for bends when turning the handlebars and the least messy cable routing.

cyccommute Thank you for the advice and picture! (That is a sick tandem bike, btw!) This is my first bike build, so I'm trying to switch to right/front brake and left/rear because I'd like to use my dominant hand for the front braking and modulation. I honestly don't know if this is a good idea, because I have another commuter bike that has right/rear and left/front -- but maybe I'll end up switching the brake cables on that bike too, or just get used to it? I haven't fully settled on the brakes for the new build yet, as the build is going very, very slowly, haha.
I'm planning to use cable-actuated hydraulic brakes, i.e., the mech-hydro hybrid. I want to learn more about bike maintenance, and even though I used to have an MTB with hydros, hydro brakes are intimidating to me. I figured that mech brakes will be easier to learn on and repair on the road if need be. You and others have recommended keeping the rear brake cable external, so that's what I'll do!

Arrowana I did manage to poke around and somehow threaded the housing through the down tube. Twice on both sides actually! I followed your suggestion (so, 2-1-4 and 1-2-5), especially since that is similar to what the Park Tool video recommends for installing shifter cables. I didn't like the look of how much the cables stuck out around the headset. So I decided to go with Crankycrank 's original suggestion of 1-1-4 and 2-2-5. Much neater looking. I wouldn't do this configuration for EVERY bike, but I hope that it will work here.

I've only just finished routing the housing, and I have yet to tune-up the shifting, not to mention installing the brake cables...

The whole reason I am even doing a custom build is because everything I need on this bike is XXS or XS sized. The drop bar width is 360mm, the crank arm is 160mm, and the frame is 44cm (XXS). You can imagine how small and cramped everything will be once I attach all my accessories later, haha! Once I finish the build, I will post pictures!!

Thanks about the tandem.

I realize now that you want to run moto-style. I don’t think it’s that much of an issue to run one bike moto and another not but it is something you’ll have to be aware of constantly on both bikes. Whatever brake arrangement you settle on, running the cables to the rear is trivial. Just give yourself enough cable or hose so that you can turn the wheel 90°. Best to have too much cable housing than too little.


I don’t know if you noticed but the tandem has a very, very, very small stoker frame. Since my wife is only 5’ tall, I’ve become something of an expert on adapting bikes to small people. In that picture of the tandem it still has 175mm cranks on the rear. I almost ruined her knees on a long ride we did with those cranks. I’ve since had Bike Smith Design shorten cranks for me. 160mm is still to long for my longish legged short wife. We went to 145mm which she like a whole bunch more. We went to 145mm cranks on all of her bikes and she is very satisfied with them. She can even stand on a climb which is not something she has been able to do over almost 50 years of bicycle riding.

This is a Specialized XXS Sirrus we got for her a couple of years ago. It had 700C wheels and too long cranks.



I decided to change out the wheels to 26” to give her more standover and a better fit. The short cranks make that drop in height possible without risking pedal strike.



Very small bikes have several challenges that larger bikes don’t. If you are thinking of doing any bikepacking with your bike, you won’t be able to use a seat bike for carrying gear. The wheel is just too close to the saddle and even the smallest seat bag would rub. You’ll need to use a rack but as you can see in the picture above, the stays on the rack can’t be used on the frame braze-on mounts. Even with Ortlieb’s longest rack stay…240mm…is too short to reach the seatstay mounts and keep the rack level. That stays on the rack are as far forward as I can get them but they are still too short. I had to go with a seat collar mount instead,

Another consideration is brake lever reach. If you are going to go with a drop bar, look for shifters that allow you to move the reach inboard for small hands. The brakes on the Sirrus are hydraulic and have reach adjustment but only for moving the levers further away from the bars! I’ve swapped the brakes over to mechanicals with levers that can be adjusted for her smaller hands.

No need to apologize for this! Many riders have such an arrangement for various reasons.

Right / front is standard in the UK

If the internal routing is dedicated 1 to 1 and 2 to 2, in other words, there is an internal tube connecting them, I would run the front derailer in 2 and the rear in 1. If you can cross the housing inside the down tube, run the front into 1 and out 2, and the rear in 2 and out 1.
I run all my bikes right front. Right rear is a throw back to DT shifters, where you wanted to shift with your right hand but still have the most powerful brake accessible to the left.