cartridge bottom bracket design
I just bought a Shimano cartridge bottom bracket, model UN 53 I believe. Pretty straightforward install, but I was surprised to note that only the right side screws into the bottom bracket shell. I got this plastic ring on the left side to fix that side of the bottom bracket, and that just seems silly. I can't see how the left side can be adequately supported when you're really hammering the cranks.
I want a bottom bracket that is equally supported on both sides of the shell. What bottom bracket can provide this? If this is a non-issue I'd sure like to know why I'm an alarmist so I can get on with the build, but having all the load borne on the right side of the shell (I can't acknowledge how a plastic sleeve, no matter how well it presses into the cartridge end, supports as well as metal to metal) just can't be good.
It's fine, don't worry about it!!!
You need a new bike
The design works on millions of other bikes. It'll work on yours.
The plastic sleeve does a fine job of supporting the non-drive side of the bottom bracket. Find something else to worry about.
BTW, if you remove the bb for a service check (you can't actually service the bb itself), remove the drive side first. The plastic sleeve will tend to break if you remove it first and the broken parts are a pain to get out of the bb shell.
I want to thank everyone for the prompt replies. I'll not worry any more about this. It's still queer in my mind's eye, but I'll find something else to worry about, like why my quill stem only goes so far down the steerer, and how many turns are enough for the locknut on my headset, since my mech said the steerer was a bit short.
Originally Posted by HillRider