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What cages do you like for MTB? Been doing shorter rides recently and it'd be nice to be free of the Camelback. Security would be my main priority.
Specialized Zee or Elite Cannibal.
Specialized Zee cages work well for me, never lost a bottle from one.
Bontrager Elite (formerly Bontrager RL) have worked flawlessly for me for years.
Elite Cuissi, with grip tape added if you want real grip. Not pretty or particularly light but you'll not lose any bottles.
As above never lost a bottle from a Zee. You can also fit the SWAT tool to the base of them
Cheap metal ones are best avoided.
The fibre glass ones (Elite?) seem pretty good.
King Cage Iris.
The standard Elite Custom Race ones are cheap and good.
Blackburn MTN cage
Tacx tao. I like mine. All eight of them.
Lezyne Flow. This one not the side loading version

Elite have a new side entry one out called the Prism, it was in FGF a few weeks back, has anyone used one?
Elite custom is/was my default, specialized rib cage and bontranger rl are good too.
But tbh cheap aluminium cages are fine if they fit the bottle, and can be bent to grip them. And suit the look of a lot of bikes better than plastic versions.
Bontrager Elite (formerly Bontrager RL) have worked flawlessly for me for years.
Plus one for these. Use them off road. In the Peak. On a cross bike. Never lost a bottle yet. There are side-entry ones too. And lots of pretty colours to match your bike.
Bottom line: whatever anyone recommends, someone else will have lost dozens of bottles with them. I wonder if some bottle / cage combinations aren't as secure as others, but the Bontrager cage seems fine with the SIS bottles, which are fairly standard.
I use this:
https://www.topeak.com/global/en/products/adjustable-cage/206-modula--cage-ex
as it's adjustable. Seems to work ok.
Arundel mandible for bling. Elite ciussi for non bling. Never lost a bottle# from either. The plastic Elites will rough up your bottles and look rubbish in no time.
#That includes the 1L SIS bottles I use for longer rides, so a proper test.
I'm a fan of the Lezyne above ^, I use them on the fork legs of my fully rigid 29+ and have never lost a bottle yet, despite some very cackhanded riding:D
King stainless steel. I can’t remember the last time I’ve lost a bottle. Might have lost my bottle though.
I have used cheapo metal ones for years with no issue. One advantage is you can bend them to get a really tight fit.
So IMO whatever metal one you can find cheapest
I've broken more of those cheap metal cages than I care to remember. Zee are doing well on all my bikes since I stopped buying the metal ones. Those Topeak adjustable ones are great as well, our kids have them on their bikes so they can just use any bottle they have to hand, rather then proper cycling ones.
I’ve had my King Ti cages for nearly 16 years now, never lost a bottle from them and they still look as good as new. Expensive but great value.
My leftfield choice would be the Monkii Cage by Free Parable. Works ideal for me mountain biking; it has never lost a bottle, can fit various styles from sports bottles to canteens and flasks, cans or cylindrically shaped food on longer rides where I use a bladder. Fact it can be quickly removed is also a plus for preserving the clean lines of you bike or when getting rad.
Avoid the cheap metal spring action ones.. Other than that I don't really have an opinion.
I've got a cheap carbon /plastic one, it works and it's really light.
My HT has inherited an elite custom from one of my road bikes.
Bottle ain't going anywhere in that thing!
Bit sticky to grab the bottle in a hurry while riding, but I don't mind that.
+ 1 for ti King Cage (pricey though) & MT ZOOM side entry for tight spaces
Tacx Deva. Light, holds bottle well and tough. Can be had for around a tenner too.
Metal one from Halfords has been fine for me. They were on sale when i got mine only £2
i have a couple of the planet x titanium ones https://www.planetx.co.uk/i/q/BOPXTIBR/planet-x-titanium-bottle-cage
doesn't seem to be a sale on them at the moment....wait a while, as I think I got them for £15 each.
Very good, never lost a bottle
Cheers, all. Opted for the Zee in the end, as my LBS stocks them and I liked the idea of getting a SWAT at some point. Didn't shed the bottle at Aberfoyle today, so feels like a good choice.
Need to get one also. Think I might need a side one as space on the Trek is limited due to the shock. Not that I have tried any yet.
Then need a decent bottle that also fits in the frame!
Then again this pic looks like the frame takes a massive bottle...
https://images.app.goo.gl/LWDsmiGAMaCxgP8w6
Not after one that big lol
aluminium ones wear out and cheap/light ones can break (same for plastic).
I have a Ti specialized one. Its silly light and haven't lost a bottle yet.
I have about 6 cheapo ones on my bikes - in more than ten years one metal one and one plastic one has broken. Once a bottle jumped out.