Sometimes ya just gotta know...

[matt glascock]

Why are the bearing balls in the lower race larger than the upper bearing balls? I have my theory to share in the form of another question. In a heavy front impact (ie casing a jump, duffing a set of whoop-de-dos), is the impact distributed over the upper and lower races similarly in terms of vector (+/- impact force magnitude ) or does the steering head act as a fulcrum of sorts.

[Bullfrog]

Well, if the impact is tending to drive the front axle toward the rear - the pressure on the steering head balls will be highest on the top/front and the bottom/rear. On the other hand, a flat landing on a "table top" will cause the highest loads to be on the top rear balls and bottom front balls. Adjusting the bearings for minimal freeplay helps spread the loads through many (most?) of the balls both on the top and the bottom. A loose steering head will tend to focus all the forces on only 2 (3? 4?) bearing balls at the top and bottom.

Why different sizes? It helps limit the development of "indexing" of the balls into matching "dents" in the top and bottom races (? micro-dents?). With different size balls, they necessarily roll out of, and into "micro-dents" at different speeds/times as the steering head turns. Same size balls would tend to "match up" and start to click into micro-dents at the same time on the top and bottom. So, (and I truly hesitate to type this in a thread I know you will read) - different size balls are a good thing.

Ed
PS:

[matt glascock]

Excellent Captain. I was up to speed with your first paragraph explaining of force bearing on the steering head associated with different impact vectors. The bearing ball explanation really makes sense now. I also wondered if the larger balls (I could never have this conversation in front of my daughters. To every thing I say, they would respond with 'That's what she said' and then I would take a reaming from my wife for purposely setting them up for a 'that's what she said' joke.)on the bottom race because it takes more of a hammering than the top under all impact situations.

Now, in a show of my impeccable maturity, I will forgo what would likely be an epic riffing session on the subject of ball variability and simply agree that different size balls are a good thing (That's what she said) .

Thanks Captain!

[viclioce]

Along the same lines, here’s my question.

Why did Hodaka decide on loose bearings instead of collared bearings. A lot of bikes use bearings in the latter caragory rather than loose. Some even offer tapered roller bearings. This would eliminate the detent dents referenced completely, right? Not that I mind the loose balls, but collared bearings were available back then too. Victor

[Bullfrog]

Bigger. Heavier. More expensive. (three strikes and you're out.)
Ed
PS: Not to mention minor (negligible?) improvement in steering characteristics for a light weight trail bike.

[JPark]

By collared bearings, I think you mean caged bearings. They offer even less load carrying capacity because there are fewer balls than a loose ball setup. They're used because they are easier to install.

Loose rollers are actually a better bet for rod small ends where the motion is similar, but not so great at the big end where the speed is high and the rollers are spinning against each other. Installing loose rollers in a small end is not as hairy as it would seem - use a dummy pin - but fishing them out of the crankcase [did you remember how many there were?] isn't optional like it is with balls all over the shop floor.

Tapered rollers offer way more surface area and pretty much eliminate all the problems other than lubrication and corrosion. It would be nice if there were a drop in roller alternative.

Most head bearings die from being too loose. Some are afraid to set them up tight figuring that they need some play. If loose, they will not distribute the load and also hammer about. Nothing like hammering on a ball bearing to wreck it.

[Bert44]

Interesting discussion. I hadn’t thought about the different size balls and issue of off set “micro dents” but it makes sense. By the way, I’ve always heard of that denting referred to as Brinnelling. This is in honour of Isambard Kingdom Brunel, an English engineer who designed ships, bridges, London’s underground water flow and many others. It’s worth YouTubing his achievements.
Another problem with caged bearings in steering heads is that preload has to be set with an accurate spacer tube whereas loose balls are much easier with the locknuts.

[matt glascock]

Yes Yes! This is great! I'm checking out Brinnelling right now!

[matt glascock]

Cool. Brinneling (Named for its inventor) is a method of determining a solid material's hardness. By driving a small metal ball of known hardness at a set force into the test material, the relative hardness of the test material can be determined by measuring the depth and diameter of the resultant indentation. The term is now used to describe the exact type of wear on the bearing races we are currently discussing. Groovie!

[JPark]

Interesting discussion. I hadn’t thought about the different size balls and issue of off set “micro dents” but it makes sense. By the way, I’ve always heard of that denting referred to as Brinnelling. This is in honour of Isambard Kingdom Brunel, an English engineer who designed ships, bridges, London’s underground water flow and many others. It’s worth YouTubing his achievements.
Another problem with caged bearings in steering heads is that preload has to be set with an accurate spacer tube whereas loose balls are much easier with the locknuts.

It's a good guess, but the guy in question was Johann August Brinell, a Swedish metallurgist, 1849 - 1925. Hence the spelling difference.

The caged bearings in steering heads are just loose balls held in a cage. There's no difference in setting them up. I've never seen cartridge bearings with a spacer like in wheels being used in a steering setup. They aren't really designed for that sort of use unless they are an angular contact type. Recent bicycles have some interesting angular cartridge, often full complement, bearings here and there and particularly in the steering.