Cages get bent. Most of the time people aren't removing and replacing the bottle as straight as they should and the cage bends. Plastic cages don't bend but they probably aren't as tight as they should be in the first place so they are slightly more prone to ejection, especially for cheaper cages. Aluminum bends easily while steel and titanium are tougher to bend.

It's nothing new either. My wife lost a water bottle in Utah that made for a dry ride back to the car. I've lost a couple of bottles while mountain biking that made for dry rides.

Of course all that went away with the invention...and use...of Camelbaks. No bottle to eject and if the Camelbak hits the ground, you have larger problems to deal with

I've never lost a water bottle while riding, but this thread is making me want to make sure the cages are tight.

It isn't just about tightness or clamping force although that can be a reason for ejection.

My experience is that water bottles eject when the lip at the top of the cage doesn't mate with the groove in the bottle correctly. This isn't the only reason but one of the main reasons.

Bad...



Good...



The higher quality bottle in the bottom picture takes significantly more effort to remove from the cage and "clicks" into the cage when inserted. The bottle in the top pic isn't even held by the cage. These are high end FSA Speed Cages pictured.

If you want clamping force then get X-Lab Gorilla or Gorilla XT cages. Together with properly shaped bottles you should never have an ejection again.
-Tim-

With the exception of the side entry cage I use on my fat bike, every plastic or carbon cage that I've used is a bottle launcher. I stick with stainless cages and I use the Elite aluminum cage with the gel inserts on my gravel bike: that thing is designed for P-R and has an iron grip.

Nah, neither the bottles nor the mounts. UA lost them along with my Cannondale bike.

The material the cage is made out of has nothing to do with the bottle ejecting or not.

Here's a former Pro's take on this

I had some Cannondale cages that used to eject bottles on a regular basis. Switched to Arundel cages and haven't had any problems.

The Arundel Looney Bin adjustable bottle cage seems pricey at $25, but might be worth it to retain an expensive thermos, or bottle of wine or whatever adult beverage you prefer.

I use a $6 Blackburn MC-1 aluminum cage. Very secure with Polar and Gatorade 24 oz bottles. If I hit anything hard enough to displace a Polar bottle I'll have a lot more to worry about than a lost bottle. It's almost too snug with Polar bottles. Just about right with the reused Gatorade bottles, but I don't expect those to last long before cracking.

Well, it does to...a certain extent. Bottle cages made of plastic (including carbon) can't bend. If the bottle ejects from the start, it will eject forever. Not much you can do to stop it. On the other hand, if the cage never ejects a bottle, it probably won't ever eject one because it stays the same shape.

Metal cages as I pointed out above can get bent with use or straight from the factory and may need to be bent back into shape so that they grip the bottle better.

From the standpoint of bottle cage interaction, a plastic cage and a plastic bottle has slightly less friction than a plastic bottle and a metal cage would.

Ejections occur in plastic or carbon cages mostly because the cage and bottle do not interface correctly. If the lip on the cage correctly engages the groove in the bottle then ejection is a non issue.

See my post above.