There's an annoying/useful bit of space under each of the bottle holders on all of my bikes; I currently strap a spare tube there (which keeps the right tube on the right bike). The tube is in a bag but the bag tends to snag and rip, and dirt/grit gets in. It also doesn't look very nice. I should be able to make much better use of this space, to hold more than just a tube, and hold it better

Spare tube strapped under bottle cage

I don't believe there's a product on the market, so I think I'd like to repurpose/make something. It should be secure against falling off, and keep the dirt and the worst of the water out.

I've found this winter that on long rides (200km+, essentially unsupported but with occasional food stops) the bike is fully loaded. I don't really want to fit the rack/panniers (weight and drag) when I'm already pushing myself quite hard, and can't add a handlebar bag because of my lights.

I've already got a top-tube bag (snacks/gels, backup battery for phone/lights), saddlebag (first aid kit, foil blanket, more snacks/gels, spare tube, jacket and shoe covers strapped underneath if not on me), 2 water bottles, tool case in 3rd bottle cage, jersey pockets full (2nd breakfast/litter, money/cards, any extra warm layers)

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    Specialized make a little box for their bikes, but I'm after something generic, and that seems to only hold their multitool and CO₂ anyway.
    – Chris H
    Commented Mar 1, 2018 at 21:30
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    you could try a wedge bag. Use the bottom of the bottle cage as you would the saddle rails and the seat tube as the seatpost.
    – mikes
    Commented Mar 2, 2018 at 0:02
  • I wonder how hard it would be to take a block of styrofoam, whittle/ carve it into the perfect shape to fix that area for your specific bike/bottle combo, then use that as a mold to wrap a couple layers of fiberglass around (using a fiber glass repair kit from automotive store), then cut the end or top off that, and you have a container for the space. Figure out how to waterproof the seem around the cut, add velcro straps to your seat and down tube.
    – SSilk
    Commented Mar 2, 2018 at 1:27
  • @SSilk I've never tried fibreglass repair like that but the idea appeals. I could be tempted to join the fibreglass to some sort of sealed plastic cap on the left. An alternative but similar method would be vacuum forming; I'd quite like to make a vacuum former. Would you like to paste your comment into an answer so I can vote it up?
    – Chris H
    Commented Mar 2, 2018 at 7:35
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    @ChrisH Done. The plastic cap is a good idea. I'm not familiar with vacuum forming. Also, Mike's idea is great, a lot less work and more portable between different bikes. Probably lighter too although it won't max out that area the way a custom hard box would.
    – SSilk
    Commented Mar 2, 2018 at 16:52

5 Answers 5


You could try a DIY custom fiberglass tool compartment for that area.

Take a block of styrofoam, whittle/ carve it into the perfect shape to fit that area for your specific bike/bottle combo, then use that as a mold to wrap 1-2 layers of fiberglass around (using a fiber glass repair kit from automotive store), then cut the end or top off that, and you have a container for the space. Figure out how to waterproof the seem around the cut, add velcro straps to your seat and down tube.

For the repair kits, you can buy them from automotive stores or Amazon and a small repair kit probably includes enough fiber to do a small project like this. The kits I have in mind are in the $20-40 USD range. Example:



If you wanted it to be a little more slick and/or lightweight, there are also DIY carbon fiber kits and carbon fiber mold kits. You're looking about 3-4x the cost of the fiberglass kits.

  • I think you're right -- fabricating something properly is the way to go. I'm thinking a two-part design at the moment but we'll see. I may yet build a vacuum former rather than using fibreglass -- I've vacuum-formed years ago and never used fibreglass (maybe that means I should try it). If I do it I'll write it up.
    – Chris H
    Commented Mar 7, 2018 at 14:19
  • Please do. Thanks for the great link, it looks very doable at home. This would probably result in a way nicer looking product and be lighter as a bonus.
    – SSilk
    Commented Mar 7, 2018 at 14:51
  • I was assuming that if I made it out of fibreglass I'd paint it to match the bike, and would probably do the same with plastic, so the finish could be similar. Either way it's a proper project
    – Chris H
    Commented Mar 7, 2018 at 15:07

Good question - I've wondered the same.

I looked at the Specialized SWAT toolbox for inspiration, but it only fit certain models of frame.

From Spec's website

Another option is to mount things directly to the waterbottle cage mounts. Here's another specialized product to do exactly that:

enter image description here https://www.specialized.com/us/en/emt-cage-mount-mtb-tool-for-right-zee-cage/p/132369

Downsides of this is that it only fits their multitool and nothing else. Also exposes the tool to a lot of dirt and muck that it wouldn't see if higher up.

I have tried a solution of using a frame mount bag right at the front of the main triangle. Advantages are that its forward weight so helps me keep the front wheel down on a steel climb, and I can put a USB battery in here for powering my gopro on long rides.

enter image description here enter image description here

Alright this bag was measured for another bike so its a bit saggy here. The pump hook gets in the way, and the downtube is much smaller and a different angle from the designed bike. Flaws - the zip is the wrong way around, and should close forward so cables can come out easier. Velcro is all wrong for this bike.

I also use a top-tube bag for more storage when on a long ride. That holds snacks and my phone running on another USB battery (because its annoying when strava stops recording.)

  • Those seem to be common problems with those triangle bags. I used to use one on my commuter. I'd have the same issue as you with the pump hook, and the velcro doesn't work with the top tube bag as well. But I might try it anyway - if I can get it to work it might stop the top tube bag dropping to one side.
    – Chris H
    Commented Mar 2, 2018 at 10:17
  • @ChrisH your top tube bag should have a head strap around the steerer tube to help it stop flopping. I'm not cuitting off the pump hook, might want it someday. Inherent floppiness of the triangle bag could be fixed by some plastic inserts on the sides, or a whole backboard with the tools strapped down, inside the bag.
    – Criggie
    Commented Mar 2, 2018 at 11:53
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    The head tube start keep that end still but but it's quite a big bag and the back end flops around. Not too much but just enough that I can't read a route sheet easily. On a smaller bag I hot-glued some stiff plastic, but that was less successful on the big bag (big enough for my power pack with built in solar panel). I always seem to need to modify my kit!
    – Chris H
    Commented Mar 2, 2018 at 12:18
  • Actually, Silca makes a little storage bag that goes where the Specialized SWAT toolbox goes. The downside is that it only attaches to Silca's own carbon cage, and the cages are $70 each. The bag attaches to the lower face of the carbon cage. Problem is, I'm not sure how it attaches to the frame. The small top tube bags an option I've considered, but I have a small frame and they will impede my water bottle access. silca.cc/collections/bottle-cages/products/…
    – Weiwen Ng
    Commented Mar 4, 2020 at 21:24

I recently saw an instructional video that you might be interested in:

While there are some off-the-shelf products that are similar (the one I use is the Z-box by Zefal, in the large/adjustable size), this video's DIY hack has the advantages of being cheap (or free if you have an extra bottle laying around that fits the bill) AND the end result is kinda stealthy, in that it doesn't look like anything worth stealing.

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    Also tennis ball tubes are great for this.
    – alex
    Commented Mar 2, 2018 at 6:14
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    The plastic tubes used in plumbing for waste water come in different diameters and have matching end-caps, screw-on or push-in with O-ring seals.
    – Carel
    Commented Mar 2, 2018 at 7:28
  • That's really nice, if I could make it short enough to go under the cage and still secure. I might well make one to replace the obvious tool case so I can go back to leaving tools on my commuter bike. Thank you and welcome.
    – Chris H
    Commented Mar 2, 2018 at 7:30
  • Downside of this, you lose a bottle cage so you're down one bottle of water. Not a problem on short rides or wet days, but on long rides that could limit your range badly.
    – Criggie
    Commented Mar 2, 2018 at 8:11
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    @Criggie I'd be inspired by this idea rather than following it, unless to replace the case in my photo. I'm bad when thirsty so anyways carry plenty of water. I have a vague idea around side access cages and offsetting the existing cage from its mount
    – Chris H
    Commented Mar 2, 2018 at 10:20

You might also be interested in the B-RAD system by Wolf Tooth.


It looks pretty adaptable and enables you to reposition the bottle(s) to allow for an accessory strap mount. For example, like this:

enter image description here

NOTE: The frame they chose to model the product doesn't look like the best use case. Removing/inserting that aft bottle deson't look easy. Regardless, they have more photos at the link above.

  • They do look handy, like nicely machined versions of what I mentioned I could make in my comment under your other answer
    – Chris H
    Commented Mar 2, 2018 at 20:30
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    Yeah, whoever took that photo wasn't thinking too hard. Commented Mar 3, 2018 at 1:01

Another option (for completeness) is to move the dead space up by moving the bottle cage down.

I hinted at this in a comment, but I've tried it recently:

lowered bottle cage

I had to swap to a cheap plastic bottle cage on the seat tube, with the top screw hole using the lower boss on the frame, and a heavy-duty cable tie at the bottom of the cage (unfortunately hidden by the crank in the photo). That then makes room for a small frame bag above (even with a 1 l bottle like the Magnum in the downtube cage). It's a bit of a stretch to get at the lowered bottle, but at least in my case it can be accessed when freewheeling.

The spare tube, tyre levers, chain link and brake pads that I used to carry under the bottle cage are now in a pouch between the seatstays and rear mudguard (visible at the top of the pump in the photo). The black cylinder with the yellow tape under the downtube is my full toolkit; the pouch containing tube etc. is a set of cheap consumable parts so the right parts are with each bike.

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    I never think to take photos when the bike is clean, only when I've got back from a filthy ride
    – Chris H
    Commented Feb 15, 2020 at 18:48
  • I like this idea. When riding, I drink from the front bottle on the downtube, and when its empty I swap them over. So the seattube bottle is only stored and accessed once. It also lowers the center of mass a bit. Personally I'd add a velcro strap around the lower toolkit and cage, so it can't pop out and be lost.
    – Criggie
    Commented Feb 15, 2020 at 22:51
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    @Criggie I used to do that, and it seems to be common practice to use the downtube bottle as the primary. I now run with electrolyte drink in the seat tube bottle, and drink from that when stopped, to keep the electrolytes trickling in. I do sometimes have a velcro strap round the tool kit, but I've bent the cage tighter (that's a an aluminium one)
    – Chris H
    Commented Feb 16, 2020 at 10:43
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    @ChrisH if you take photos when the bike is clean, we'd all assume you never ride it. This way, we know they get used. :)
    – FreeMan
    Commented Mar 5, 2020 at 20:18

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