EPOisDope

I currently have a Rotor Aldhu 30mm crank. It seems like every 500 miles I need to "tighten" the preload nut in order to keep it from ticking when out of the saddle. The 2mm bolt itself that attaches the preload nut to the crank remains snug, meaning that the preload nut itself isn't moving - it just seems that as the bottom bracket bearings get seated, they need additional preload. I put enough preload on the crank each time that it doesn't spin as freely as it should, but it then spins easier and easier after each 100 miles or so, until it no longer has enough preload and starts ticking again with any significant lateral load a few hundred miles later. I can understand that for the first 250 - 500 miles or so with a new bottom bracket, but it seems odd that I have to do this every 500 miles or so. Putting grease on the crank spindle helps quiet things down, but I left the preload nut untouched for 1000 or so miles, I'd likely be able to feel a tiny bit of play in the cranks if I grabbed both pedals with my hands and tried to move the crank from side to side. It was also like this with a Rotor 3D+ 30mm crank on a different frame, both with threaded BBs. Do other people experience the same thing with Rotor cranks, or probably any cranks with a preload nut as opposed to a wavy washer? Up until now, I've always used Rotor BSA30 or ITA30 BBs, but this time around I went with an Enduro ITA BB, and am fighting the same battle. The Enduro BB also came with a wavy washer which I haven't yet installed. I'm now thinking of loosening up the preload nut enough to put the wavy washer in there that came with the BB so that I don't have to keep messing with, and eventually stripping, the 2mm bolt, but I have a hard time believing that a wavy washer is the perfect solution here. Wavy washers to me seem like a "duct tape"-level answer to the problem.

dabac

Welcome to the questionable design practices of the bicycling world.
The type of bearings used in outboard bearing bottom brackets do not tolerate axial loads very well, and axial load is what your preload is. By chasing what you think is the ideal operating state, you’re wearing them out.
If you insist on using a BB style built around a not-so-clever choice of bearing type, a wavy washer is a less bad option than manually adjusted preload.

Andrew R Stewart 

This! dabac hits the cable on it's head.

One problem that the bike industry has suffered with since before the Wright brothers is maintaining tolerances on such a low cost point product. How do you produce a bike that will work well enough for as long as the consumer accepts fo as little as they are willing to pay for? By employing components that expand the tolerance for component interfaces (think BB shells and head tubes as examples) the industry can get closer to the above goal.

Angular contact bearings allow for more bearing misalignments, whether from the factory or during the stress/flexing that happens when a bike is ridden. The common radial contact cartridge bearings used in most bike applications don't handle axial loads anywhere as well.

Any bearing's preloads speaks directly to its life span so a system that allows for adjustment to the preload allows greater bearing to bearing distance tolerance (or the manor that the bearings are kept apart from each other can be held to a loose spec). Remember what I said about the smaller the ball the less the load capacity? So too with the ball's ability to roll along a less than perfect surface. (Ride/coast a 12" wheeled bike over a curb or pothole then a 700c bike over the same bumps. For the same tire profile/pressure which feels smoother/faster?). The smaller balls that most bike speced cartridge bearings use contribute to the design (BB or headset as example) not tolerating a somewhat worn race or misalignments.

But all this mechanical design stuff isn't what the buying public wants to hear or embrace when they are in the buying mood. They want the promise of more sizzle. And the new bike will provide that, on the test ride and somewhat longer. But not for as long as the more traditional designs did IME. Andy

EPOisDope

Just out of curiosity, if I wanted to have an existing 11 / 12 spd crank / BB combination that WAS properly engineered (i.e. spins freely / good durability / hassle-free preload), what would that be? I've always had good luck as far as consistent / hassle-free preload, at least reasonable bearing life, etc. with Shimano cranks / bottom brackets. Let's ignore the fact that modern Shimano cranks that spontaneously combust for now! While I've seen several people / Youtubers point out flaws in many BB types, such as GXP overloading the non-drive-side bearings, I don't often hear of GOOD crank / BB combinations, much like I hardly ever hear of well-made bike frames. Do we have to go back to square taper BBs, or some other sealed cartridge type BB?

Andrew R Stewart 

Shimano cranks don't explode. They do have very few production issues with the hollow ones and those few get more attention than others do. when you're the big guy many take aim at you. I remember a comment by a helmet company. He said that bell had a lot of claims against them. Not from bad products but from their having the big insurance policy

Outside of that item you seem to have answered your own question. Andy

silverado8405

To answer the second question: a good quality angular contact bearing with a properly sized spacer for the distance between the inside of the inner races to help eliminate as much overloading and play as possible and take the guesswork out of “how much preload do I need”.