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Bearings, bearings, bearings(12 posts)

Bearings, bearings, bearingsMarlon
Mar 12, 2002 1:41 PM
I'm starting to get curious about bearings in general, after doing a couple of hub and pedal repacks on my bike and my friends' bikes.

Generally, what are the factors that are important in buying bearings? My first guesses (for sealed bearings) would be:

1) Lubricant (some sort of grease for increased longevity and performance given possible contamination, but would there be any performance upgrade in using oils?)
2) Type of seal (contact to keep out contaminants, but would the material of the seal make a difference, say, a teflon versus a nitrile seal?)
3) Axial/Radial clearances (how loose an internal clearance can you get to increase bearing speed?)
4) Ball material (would it be worth it to get stainless steel versus normal steel? What about ceramic balls? How would this affect longevity of the bearing?)
5) Cleanliness of bearing assembly (it's no good if it isn't already free of contaminants to begin with)
6) Retaining cage (would a nylon cage help to deal with unexpected shock loads?)

If someone can add to the discussion, I'd be happy to learn more.
Uh, quality?Kerry
Mar 12, 2002 4:50 PM
You left out the key point - bearing quality. There is quite a range in quality. The common US rating is the ABEC scale (Annular Bearing Engineers' Committee), with a rating from 1 (lowest) to 9 (highest). The European rating is (no surprise) ISO (lower numbers = better, except 0 is the lowest quality). Price is generally comensurate. You will have a hard time finding out most of the other items you list, but better bearings tend to have better grease, better seals, better assembly, etc. By definition, a bearing cage only serves to keep the bearings from falling out when the unit is taken apart and to aid in assembly - the bearings take the shock, not the cage.
But how useful are ABEC ratings?Marlon
Mar 12, 2002 7:47 PM
I heard from a friend who inline skates that the ABEC scale only measures bearing precision, and he said that while having bearings with higher ABEC ratings could theoretically increase top speed, the bearings would have to be used under very controlled conditions in order to take advantage of the increased precision - something like eliminating all sources of vibration and possible shocks. He also said that ABEC 1 bearings were rated for use at a maximum of around 30,000+ rpm, which seems pretty fast for me, given that ABEC 1 is the lowest quality bearing, relatively speaking. Bottom line, I was told that buying bearings with ratings better than ABEC 3 for low rpm use such as in inline skating (and I guess for cycling) was a waste of money, and that I should worry more about the lube used inside the bearing unit.
But how useful are ABEC ratings?slow-ron
Mar 13, 2002 9:26 AM
You are correct, ABEC ratings are a measure of precision. ABEC includes runout, width, bore o.d. & bore i.d. This does not include materials, assembly workmanship, seals, quality of the grease, etc. ABEC ratings are almost a non issue when working with mechanical devices that are non-precision i.e, bikes, skateboards, in-line skates.

What you should look for, in my opinion, is a bearing manufacturer with a good reputation since you're obviously not going to set up a test evaluation program. A Torrington rep. once told me that almost all the balls used throughout the world in ball bearings are supplied from a couple sources so the variation comes from the assembly and the cages & seals. It used to be that anything off shore was considered poor quality but the bearings from Singapore are very good. Chinese bearings are quickly improving too.

Here's who I like with my experience in bearing specification.

Torrington-Fafnir
FAG
NTN

The beauty of sealed ball bearings over cup&cone is that they are disposable. If you select a cheap ball bearing and it fails, you simply pop another one into the hub. Most bearing cups are pressed into hubs and when they get pitted the hub is trash.
Racegrzy
Mar 13, 2002 3:20 PM
What really matters is the quality of the race - the thing that the bearings come in contact with and ride on. The level of precision on a typical ball bearing is very high. However, the quality of the race is what really varies by manufacturer and really what you're buying. You can buy the most expensvie, highest precision balls in the world, but if the races are junk then it matters not. The same could be said about the ball bearings, but it is much harder to buy low quality balls. Stainless steel is actually softer than normal steel, but has a higher toughness (it can be deformed further before ylelding) and is corrosion resistent. SS is generally inferior for precision machinery UNLESS corrosion is an issue. Running without seals and grease will make a bearing "faster", but it won't last long.

In the grand scheme of things the amount of variation in frictional loads between decent bearing setups is marginal. A much larger effect is the inflation pressure you run in your tires and how low you can get on your bike to reduce frontal area. You can tell very little by spinning a wheel with no load on it unless it's some POS and way out of adjustment. If you keep the bearings and races clean, lubed and properly adjusted you'll be fine. If you think that getting ball bearings made from pure "unobtainium" is going to make you faster you're in for dissappointment. The military-industrial complex has had a lot of experience with ball bearings and most of the bugs have been worked out. If your componentry is coming from China then maybe you should be concerned. In general precision bearings are meant to run for something like 50,000 continuous hours at maximum rated load and speed - none of whihc we even come close to on a bicycle. The real virute of precision bearing s for bikes is that you don't have to maintian, adjust, and clean loose races - - you can spend more time riding your bike and less maintaining it.
What about ceramic nitrate? Worth the effort/cost?(nm)jim hubbard
Mar 13, 2002 4:34 PM
What about ceramic nitrate? Worth the effort/cost?(nm)slow-ron
Mar 14, 2002 7:00 AM
the ceramic balls have a better surface finish than steel so they reduce friction. The only time I've seen these used is in high speed precision applications or when there's an issue of the steel balls getting welded to the races. I guess if you can get them for around the same price or slightly higher than steel balls it would be O.K. but if the cost is much higher I don't know if it's worth it.

I've never used them but I'm guessing that for the slow speeds of bicycles you'd never know the difference.
Agreedgrzy
Mar 14, 2002 9:43 AM
If a bearing has a better surface finish then it should have less friction, but given the nature of point contact there will be some deformation. If the ball is significantly harder than the race then the race will undergo all of the deformation and may wear out prematurely. A bearing assembly is a dynamic system and all of the parts must work together. A mistmatch in the parts means that somethings will wear too quickly. Typical failure modes for bearing assemblies are galling, pitting, brinelling, etc. Once you have bits of ceramic particles floating around things will go south quickly.

Given the magnitude of the bearing frictional forces are many orders below the other sources I don't see how you could justify it. An emprical arguement would be along the lines of given the absurd amounts of money people are willing to pay for bike parts they would certainly go for any bearing that would provide a measurable advantage. This doesn't necessarily prove anything, but you should acknowledge that we can't be the first people to think about bearings for bikes - if there was an advantage, even a small one, someone would be doing it - cost be damned. I also wonder how well ceramic bearings would take the normal impacts and shock loads transfered from the road - you might see the ceramic balls fracturing, which would really slow you down. It should be noted that heat related failure modes aren't typical for bikes - mostly it's contamination, improper lubrication and adjustment. A ceramic setup doesn't address any of these issues.
Agreed x 2speedisgood
Mar 17, 2002 8:51 PM
I read on another board that ceramic bearings are very brittle and don't handle deformation very well. Again, not ideal for bikes hubs. HOWEVER, check out Zipp's super-duper fancy hubs: http://www.zipp.com/hubs/z3_series.html

Wonder what they're thinking and how long these things would last in real-world racing conditions.
Nice postNessism
Mar 15, 2002 11:04 AM
The information about the stainless vs. ferrous steel ball bearings is interesting and brings up the questions of which is better for bicycle use? In my experience, water contamination inside the bearings is a real issue for bicycle applications. I've had quite a few "cartridge bearings" fail due to grease breakdown/water intrusion. While theory has it that these sealed bearings should have an advantage over loose ball setups, in the end this has proven not to be true. I think in many cases, "sealed bearings" are not sealed all that well. I've taken to pry the seals off of my catridge bearing components and grease them just as I would with a loose ball component. Of course, the loose ball parts are easier to service.

Another comment relates to the size of the balls used on loose ball components vs. cartridge bearing components. In many cases, but not all, the loose ball component uses larger balls in the bearings. These larger balls will distribute the stresses better and last longer.

Just rambling.

Ed
Deep Thoughts on Wheel BearingsUncle Tim
Mar 14, 2002 9:03 AM
I have always wondered about the secret life of ball bearings. Is there any of you engineer types that can tell me what their working life is like?

What happens to the bearings as the bicycle wheel spins? I know the bearings roll individually, but do they all roll the same way? I would think that as the bicycle wheel rolls, the bearings rotate around the hub. If this is the case, which way would they rotate? Would they rotate in the same direction as the rim or would they counteract that movement?

And what about heat in a well greased hub? I know that I have removed bearings from poorly maintained bikes that look as though they've been scorched. In hot weather, will well packed bearings built up a lot of heat? What about well packed bearings on a cold ride? Do they build up enough friction to warm up or will they stay around the air temperature?

Now there's something to think about!
Deep Thoughts on Wheel BearingsMarlon
Mar 14, 2002 12:29 PM
Don't know all the answers, but I'll give a few guesses...

I'd figure that in a sealed cartridge bearing unit, since the ball bearings rotate in the same direction, they'll "roll" in the same direction as the rim.

I'm not quite sure how hot the bearings would get, but I reason that the repeated heat from using your bearings would cause the gradual breakdown of the lube, causing it to escape from the units (hence the "weepage" you see from bearings), leading to increased friction inside the bearing, and eventual breakdown of the entire unit. The "scorching" you see on bearings from poorly maintained bikes would be (my guess) from those bearings not having had enough lubrication around them. One question though: does the lubrication breakdown follow an exponential pattern? If so, it would make sense to replace your bearings as soon as you notice that they're not rolling quite as smoothly, since the degredation of the bearings would occur at an increasing rate.

I don't think our bikes go fast enough to build up enough heat in the bearings, otherwise someone would have probably created bearings with heat sinks. As for cold weather biking and bearings... if you're using a grease lubricant, it's already solid under normal (room) temperatures, and I don't think the grease solidifies as a linear function of temperature. With an oil lube, it's even less of an issue, I'd think. So heating the bearings wouldn't really matter - the bearings wouldn't freeze up into a solid chunk under cold weather (unless you're at absolute zero in space).

Of course, I could be completely wrong about everything I just wrote.