Bontrager XXX Carbon Aero Handlebars vs Shimano 9000 shifter

Discuss light weight issues concerning road bikes & parts.
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Posts: 29
Joined: Sun Jun 20, 2010 6:55 am

by wootenlakeguy

I'm trying to build up a new bike using the Bontrager XXX Carbon Aero handlebars and the Shimano Dura Ace 9000 mechanical gruppo. These bars don't weigh much more than standard bars (230 grams) but still offer an aerodynamic advantage and are comfortable while riding on the flat tops. When I received the bars I was pleased to see holes on either side near the shift lever which I thought would allow me to route the brake and shift cable housings internally through the bars to where they exit near the stem. However, on the 9000 shift levers, both the brake and gear shift cable housings exit the shifter body on one side, the inside of the handlebar.

Unfortunately, using only the hole provided on the inside of the handlebar makes it difficult to route both cables through the same hole. It can be done (barely), but the housings are forced into such a small diameter bend that friction is introduced and this affects shifting performance. There also isn't any way to wrap either housing around the handlebar to utilize the unused outer hole in the handlebar. Because of the shape of the handlebar, the hole near the stem is large enough for the exit of two housings, but currently I can't get both housings to fit internally near the shift levers without introducing friction. That being the case, the only alternative seems to be to run either the brake or shift housing on the exterior of the handlebar which doesn't allow a clean installation and mostly defeats the purpose of the flattened aero section.

I've talked with Trek (Bontrager distributor), but all they've told me is the Madone 7.7 is configured with exactly this build and they're able to make it work. They also said I shouldn't attempt to modify the bars in any way or it would void the warranty.

I've used the search function about this specific issue and can't find any reference. Has anyone else addressed this problem? It looks like all I'd have to do is bevel the inside hole near the shift lever so the housings aren't forced to make a 90 degree bend in such a short distance. By beveling both the leading and trailing edge of the hole appropriately, the housings would only have to bend about 45 degrees which would help to mitigate friction. Additionally, since the hole wouldn't be enlarged appreciably, I don't think structural integrity would be jeopardized.

Any advice appreciated.

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by Ozrider

Go into a Trek dealer and have a look how it's routed.
It seems stupid to me that Shimano oh as gone this route as most bars accomodate one cable exiting from Left side of shifter and one from Right side of shifter. My Enve bars have one groove in front of bar and one behind bar, and changing to DA 9000 has both cables running behind the bar now.

My Madone is still on SRAM Red using the XXX Aero bar, and I can see your dilemma. Not an ideal way to run cables at all.
Ozrider - Western Australia
Parlee Z5 XL (6055g/13.32lbs) Trek Madone 5.9 (7052-7500g)Jonesman Columbus Spirit (8680g)
Chase your dreams - it's only impossible until it's done

by Weenie

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by Svetty

Surely the issue isn't with Shimano but with Bontrager/Trek! They must have known that with the massive Shimano user base out there that the hole needed to facilitate smooth cable runs. :D

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by FIJIGabe

I don't think it's an issue with the shifters or the bar. I think the solution in your case is to run the cables through liners in the handlebar. Since Trek/Bontrager assumes you are installing the part at a retailer (who can provide the liner), they don't include it with the handlebar, but I think that's the proper way to go in your case (liners from the shifters to the end of the handlebar, then regular housing from there on.
Madone 9
Madone 5

Madone 4, Cobia. I own a lot of Treks.

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by mattyNor

See if you can find any 4mm brake housing at your lbs, may cost a pretty penny though....

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by wootenlakeguy

I don't think they make 4MM brake housings. After all, shift cables which are 1.2MM in diameter use 4MM housings and with brake cables being 1.5MM, there'd probably be friction introduced by using the same size housings. Besides, I don't think gaining a single MM over a traditional 4MM shift and 5MM brake housing would make a significant difference. The required bend would be reduced by a few degrees, but would still be close to 90 degrees within the less than one inch width of the handlebar at the location of the entry hole.

Another suggestion was to simply use liners instead of housings. This would not only reduce the diameter significantly but would also allow the cable to bend more freely. Unfortunately, I think it would also introduce a lot of compression into the system. After all, cable housings are specifically designed not to compress, but a small diameter plastic liner isn't. This could possibly be tolerated for the brake cable (would make brakes mushy with poor modulation), but would certainly make shifting iffy.

I do appreciate your suggestions.

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by CXTony

Use a bead-style housing like nokon to deal with bends?

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Joined: Sun Jun 20, 2010 6:55 am

by wootenlakeguy

Your bead style housing sounds intriguing. I had dismissed the Nokon or the Powercordz Swift system because I didn't care for the beaded housing appearance. However, for my application, they'd only be exposed for four or five inches where they exit the handlebars near the head tube and enter the frame. I'll hope to get away with a standard housing for the front brake which has a longer run of housing exposed. After exiting the frame near the rear derailleur or rear brake, since severe bends aren't an issue, I could simply switch back to normal housings.

I'm attempting a weight watcher build with a ready to ride weight of less than 6 KG, so every gram counts. Since these beads are able to make tighter bends and are lighter than a standard housing, they sound like the best available option.

Thanks for the suggestion

by Weenie

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Joined: Sun Jun 20, 2010 6:55 am

by wootenlakeguy

After reviewing the recommendations, I've decided using a beaded housing will best address my problem of a tight bend into the interior of my Bontrager XXX carbon aero handlebars. Since Bontrager advises against enlarging the entry hole, this seems my only option. The systems I'm considering in alphabetical order are the Aican Bungarus, Alligator Ilink, Nokon and Power Cordz Swift. After reviewing the information on this site, I've concluded there's not enough difference in weight or cost for these housings to be an important factor.

What I haven't seen addressed specifically is how well each of these four systems will tolerate a one inch 90 degree bend without introducing enough friction to adversely affect shifting or braking performance.

Does anyone have first hand comparative experience regarding the flexibility of these four systems. Does one stand out above the rest or since they're all beaded housings, do they offer comparable flexibility. Because of weight, I'll probably run Power Cordz cables through whichever housing I chose so would welcome advice on that as well.

Thanks again for your comments.

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