3T Mistral Di2 Cable Routing

[shredz2000]

Hi Everyone, I'm new to the forum, but have been checking it out lately for ideas as I recently bought a Kestrel 4000 LTD. I have an idea of my own that I would like to share. The Kestrel has DA Di2 components, but was not optimally set up when built. Kestrel made 100 of these bikes in 2011 and I bought one that was used, but still completely stock. The aerobars are 3T Mistral. The bike came with the Di2 TT bar end shifters SW-7971, but not with the ST-7971 brake/shifters because the Mistral bar does not have internal routing for Di2 (though other higher end 3T aerobars now do). I've wanted a Kestrel 4000 frame ever since it was (re)introduced as a production model at the end of 2010. The LTD has been optimized for Di2, but why they chose a bar that doesnt internally route Di2 on a top-of-the-line TT bike I will never know. For that price they could have put on a Pro Evo Missile or HED Corsair, but I digress.

The budget I had covered getting the bike at a very reasonable price and allowed me to purchase the ST-7971 separately. It wasnt until I went to install the brake/shifters and pulled out the existing brakes that I realized I was going to need to figure out how to cleanly route the Di2 cable to the brake/shifters. I'm a bit of a perfectionist and after finally getting my dream bike with DA Di2 I want the thing to be sleek, clean, and mean, and not half-assed. I cant afford to spend another $500-$1000 right now on a new base bar/cockpit that has Di2 fully routed internally, plus I dont want to mess with the position I've dialed in right before I start racing this season. So that got me thinking this week and here is what I have come up with for my DIY Di2 ST-7971 cable routing for the 3T Mistral (and any base bar that is not Di2 internally routed).

After getting the connectors covered with heat shrink tubing I taped the Di2 cable to the bullhorn on the Mistral. The connector sits about 3/4s of the way towards the back of the bullhorn. There is enough clearance for me to grip the bullhorn when braking or shifting without feeling the protruding connector under the bar tape, but if I'm climbing and want to slide my hand rearward at all its really bulky and feels weird. Basically you know the connector is under there. The bullhorns on the Mistral seem longer than most TT base bars and if they were shorter the Di2 connector would sit directly underneath part of the base wing and not extend out to the bullhorns, and therefore be completely out of the way of the grip. Part A of this project was to cut the bullhorns down, since there seems to be a longer handle than really necessary on a TT base bar. This is pretty simple to do if you have ever cut carbon fiber extensions. I used a fine-tooth hacksaw, wrapped the bullhorn in tape and lopped off about 1.5" from each.

With the bullhorns cut down part B of the project was to secure the Di2 cable to the rear edge underneath the wing where it would not disturb the airflow. I tried taping it down with electrical tape, and this does the job, but it doesnt look all that great, and with electrical tape the potential is there for it to start sliding around if it gets wet or heats up in the sun, and it gets all gooey and nasty. I wanted to keep the aerodynamics of the base wing as unaltered as possible and use something that wouldnt have the issues with tape. I came up with using liquid rubber. You can get it in a can that can be sprayed or it can be brushed on. I've tried Plasti-Dip. It easily adheres to painted surfaces and can be easily removed if you ever want to take it off without damaging the paint.

Using masking tape I taped a channel where I wanted to lay the Di2 cable and then 'tacked' a small area with the spray at the junction of the bullhorn and wing to hold the cable in place. Once this tacked area set up a little I then sprayed the entire length of the cable on the underside of the wing. This will hold the cable securely in place giving it a protective coating in case it gets scraped in any way. The heat shrink tubing provides good protection for the connector joins and I sprayed right up this. I did not used the dual walled tubing because you can use the liquid rubber to seal the ends of the heat shrink tube around the cable and the regular heat shrink tubing can easily be removed. I left the connectors uncovered by the liquid rubber so I can easily get at them should I need to take the shifter off. The liquid rubber will just peel away if you want to remove the entire cable from the bar.

For the cost of the liquid rubber can I was able to keep my position the way I wanted with this particular aerobar and not spend hundreds on a new one and have to try to get the position to match or get used to a new position. Maybe I'll replace the Mistral at some point with a newer 3T bar that has internal routing, but for now this seems like its going to work really well.

[pritchet74]

How about some pics?

I am about 3/4 of the way thru a nice bottle of Merlot, so pics would help me greatly. This sounds great, but I am more of a visual guy.

[shredz2000]

I should have some pics to put up in the next few days. I've been adding a few more layers of the Plasti-Dip over the weekend to build up the bond over the cable and will post them when I'm finished. Something that would have improved the process that I thought of last night would be to put a very thin layer of wax underneath the Di2 cable so that its already fully stuck to the length of the wing. Trying to tack areas was a bit of a pain as the cable wanted to flop around, but it did work.

[Ypsylon]

Or maybe some electrical tape to hold it in place while the plati stuff dries? I think I know what you did, but pics would be appreciated.

[shredz2000]

Okay, finally got some pics to put up. The first one shows what it looked like 24 hours after applying the first coat to get the cable stuck to the wing. This was definitely the most difficult layer to apply as it forms the basis of the bond between the Plasti and the painted surface. I fully coated it 3 times on the first layer allowing about 20-30 minutes in between each spraying to let it start to set up. I removed the masking tape about an hour after the last spray. This can be a bit tricky as the outer-most coat has already turned to rubber and may require a razor blade with a very light touch to the edge of the masking tape to fully separate. The bottom layers around the cable where it was built up were still pretty liquid. The cable was firmly stuck to the wing after just that first layer.

The second photo shows how I taped the channel before applying the second layer. The third photo shows the second layer applied. Again I did 3 coats allowing about 20 minutes in between each for it to start to set up. You can tell its ready because the Plasti goes from looking very liquid and glossy to having a more dull shine.

Any over-spray is easy to clean up and you can just wipe it off with your finger. Now that all the layers are dried I am going to take a razor blade and clean up the edges where the plasti meets the wing to get a nice, smooth line. It pretty much looks like electrical tape, but has a pretty strong bond.

Taping and spraying only take minutes, its the half hour or so between coats and the multiple layers that take a little bit of time with this, but so far I'm pretty happy with the results.