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I recently purchased a Trek Domane AL 3 Disc. It has 4 mounting supports.

2 inside the frame for water bottle cages

1 next to the stem

1 on the frame bottom

I wonder if anyone know what kind of accessory you can put on the support next to the stem?

Also, the ones in the bottom are really for accessories or are holding any internal piece? I was thinking of adding a small pump there.

Photo of a Trek Domane with a red box highlighting the bottle braze-ons on the seat tube and the top of the down tube; another box shows the braze-ons beneath the down tube and a third box shows indicates the braze-ons on the top of the top tube

3 Answers 3

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The braze-ons beneath the down tube are traditionally for mounting a third bottle cage. Of course that bottle is more exposed to road dirt than the others, so many people use it for various utility purposes. (You can get water-bottle-shaped repair kits that will fit in there, batteries, air reservoirs for air horns and I'm sure other things as well.) It would definitely be a reasonable place to mount a small pump.

Braze-ons on the top tube are relatively new, but there are a number of small bags available that bolt on there. The advantage of these bags over normal (velcro-attached) top tube bags is that they are better affixed, so they're not going to start to tip over on you as you're pulling out a bar. You can also get computer mounts for some brands of bike computer/navigation systems.

Cable management might be an issue, but a bottle-shaped battery pack with USB out could be very useful for long rides or an older computer whose battery no longer has good endurance.

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  • thank you some much DavidW. I'll definitely go for the water-bottle-shaped repair kit. Jun 7, 2021 at 21:56
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    Those bottom mounts are loved by bike packers as a spot to store fuel bottles as well. Jun 8, 2021 at 0:48
  • @whatsisname when bike camping I use that position for my fuel bottle, otherwise for tools (note, tool kits can get wet and stay wet down there, leading to rust). In fact I've made a mini cage for a smaller fuel bottle (discussed here)
    – Chris H
    Jun 8, 2021 at 8:40
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    I wouldn't put a battery bank down there in anything but the driest climate. They're often not as well sealed as they say (and USB connectors aren't usually sealed at all). Even with full mudguards that's a very wet location if there are puddles
    – Chris H
    Jun 8, 2021 at 8:41
  • @whatsisname You mean you would carry a heavy gasoline stove instead of a light gas one? Jun 8, 2021 at 12:25
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+100

I would mention that, at least for the carbon bikes, the two on the downtube are not for mounting external accessories. To quote from the Domane SLR-SL FAQ document:

What are those two holes on the bottom of the downtube? These hold the cable routing guide and, if used, Di2 battery. They are not spaced appropriately for a third bottle.

Edit: As has been pointed out the carbon and aluminium models are different, I've since discovered in one of trek's own videos that the aluminium model does support using the downtube for mounting bottles

youtube screenshot from Trek's channel showing three bottles on the bike Source: (at 1:54)

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  • Welcome to the site - have you a link to this FAQ? I found trek.scene7.com/is/content/TrekBicycleProducts/Asset%20Library/… but that's not the same text
    – Criggie
    May 29, 2022 at 19:40
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    To Criggie's question, I'd also ask you to confirm that the carbon Domanes even have the 3rd bottle cage and bento box mounts. Looking on Trek's site, it doesn't appear that they do. @Criggie gave a link to the 2020 carbon Domanes; the OP asked about 2021 aluminum Domanes. It's possible the 2021/22 carbon Domanes have changed, but I did just look on Trek's site.
    – Weiwen Ng
    May 30, 2022 at 3:10
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    @Criggie sure it's on this page under the "bike tech" subheading, labeled "FAQ-Domane SLR/SL" trekbikes.com/gb/en_GB/bikes/road-bikes/performance-road-bikes/… The document itself is hosted externally for some reason, but for convenience I've linked it here: retailerassetsprd.blob.core.windows.net/techassets/… May 31, 2022 at 10:02
  • Bounty was awarded for the edit.
    – Criggie
    Jun 1, 2022 at 11:06
  • I saw a current model carbon Domane in my bike store. Roshan is correct, there are a couple of apparent mount points on the underside of the downtube. But they are clearly not for bottle cages.
    – Weiwen Ng
    Jun 2, 2022 at 19:18
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Several manufacturers, (Apidura being just one) make top tube bags that use a bolt on mount. Some use a shouldered screw for the mount. This mates to a keyhole shaped holes in the bag frame. It slips on and locks into position. You can search for bolt-on top tube bags to find a model that fits tour needs.

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  • thanks for your answer mikes. I'll picking the next answer as correct because he covered the braze-ons beneath the down tube Jun 7, 2021 at 21:58

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