Bearings is a hot topic for me, as for many bikeheads. Being a former mechanic worked on quite a lot of engines, cars and bikes, I had lots of experience with them; especially why and how they fail. Understanding bearings is useful if you’ re shopping, replacing parts – because, when you buy a particular component, like hubs or cranksets, you’ re also getting a certain kind of bearing type, which directly effects performance, longevity and of course, price of the component on the long run.
There are many “half-truths” or bullshit regarding bearings in bike industry. But let me quickly explain types of bearings used in bikes.
1.Cup and cone bearings
Shimano’s favorite hub bearing type. This is the best bearing type for hubs: it rolls nice, cheap, and handles both radial and axial forces best.
This is a “bearing system” that is integral to the part, like a hub or pedal. “Cup” is integrated to the hub or pedal body, and tiny steel balls are secured to the cup by “cone”, which is attached to an axle on the hub, or spindle on the pedal. This is far superior to cassette bearings, because cassette bearings on bikes are tiny, and need to resist quite a lot of force compared to their sizes.
Cup and cone bearings have 2 flaws: unlike cassette bearings with integral seals, like the ones with 2RS designation, this system relies on seals that attached to the parts. Higher end Shimano hubs are bulletproof. I wouldn’t recommend anything below SLX for MTB, and 105 for road. XT and XTR design differs from others: these have plastic caged, very robust ball bearings with boron nitrite treated cups. Boron nitrite is, in marketing speak, “ceramic coated”. They also have oversize aluminium axles. XT and XTR is internally the same. I don’t know why XTR is lighter but, probably Shimano shaved off some more aluminium. Do not believe anyone who says Deore or SLX is better, XT and XTR fails. No.
Looks like a crude design, but it is not, and interestingly, it needs proper and regular maintenance then other hubs with cassette bearings. Because, as I said before, they don’t have the best sealing around. Yes; cup and cone system needs regular maintenance. This is the second downside to them. And maintenance is hard, because you have to correctly torque the cups. Seems like its a dark art with no proper tools to make it easy for you. If you don’t adjust them well enough, you’ll destroy the cups, break the axles or start a nuclear war.
Do not use cheap balls when you have to replace them. This is a great setback for me, and should be anyone else, too – these cheap looking steel balls have grades, and price hugely varies how good the grade is. Unfortunately, at least for me, there is no way to differenciate a junk from the gold.
Cartridge bearings are for the lazy. In most hubs, they’re easier to replace. Such as Mavic hubs, which use standard, off-the-shelf bearings, and are easy to service. Not every hub: some DT Swiss hubs I came across needs some special tools for servicing, which is nothing a machine shop cannot make, but that means money and time. Cartridge bearings are also used on bottom brackets, headsets, pedals, even in rear derailleur jockey wheels.
If you don’t like servicing your bike much, get hubs/wheelsets with cartridge bearings: and get ones with off-the-shelf bearings, because “custom” bearings are not good as premium brands like SKF, INA, or NSK and are generally crazy expensive. I like the idea of choosing bearing quality: premium brands are generally 10x more expensive then Chinese cassette bearings. If I want to ride my bike in sand and heavy rain, I’ll probably buy some junk bearings. Even the best bearings get easily worn out in case of water or dirt ingress.
Cartridge bearings are not designed to work on bikes, though. They are not designed to handle radial loads. Does it make difference? In some cases, yes. If your hub has huge bearings with big balls, then no problem. This is not the case with bikes, though. We want smaller, lighter parts and cartridge bearings are heavy and bulky. Cartridge bearings in bikes sometimes have ridiculously small balls in them, like in the GXP or Hollowtech II bottom brackets, or headsets. These bearings dig into races quite easily, so they don’t last long. Cars have cartridge bearings in hubs, but they are HUGE.
Radial loads are not much on bikes. The real problem is, cassette bearings are tiny, balls are tiny, and they have to resist huge axial forces compared to their size, but also some radial loads, too. Combine all this, makes a huge dealbreaker.
I have a trusty old XTR 980 rear derailleur, which is perfect for me in every sense, except one huge flaw: to make it “fancier”, Shimano used cartridge bearings in pulleys, which is absurd. They are so small that they rip off when you try to remove them, because races are thin as razor. So after a few rides in rain, they go bust, guaranteed. They cost as much as a mid-range derailleur. I replaced them with proper ones having a bushing instead, and it runs perfectly one. Probably that costs me 0.001 watts.
3. Roller bearings
Roller bearings replaces balls with hardened steel cylinders. They are much robust than anything else because these cylinders have huge surface area compared to balls. They are also easy on the races, because the pressure area is also bigger.
These things are heavy and have more friction. I’m not sure if they really cause more friction in some cases, because tiny balls in cartridge bearings are not smooth under load, too. (they tend to spin like crazy when no force applied, so people tend to think they are nice!).
SKF uses such bearings on their square taper bottom brackets. Other than that, I don’t see any other applications on bikes. I still tend to think it’s the best bearing type to be used on bikes, along with needle bearings, which is also super lightweight.
I do not take MOST ceramic bearings seriously. It’s a fashion statement. In most cases, the races are steel, and balls grind races. There are also full ceramic bearings, very hard to find and super expensive, or Chinese alternatives that are absolute junk. You know them from ultra expensive, carbon fiber derailleur cages with jockey wheels having the size of BMX wheels. They are the most expensive fidget spinners in the world, and won’t make you fast, but broke.
A word on balls
Cup and cone system looks very primitive, but in fact, its hard to adjust and pick correct balls. It’s not just size that matters. Steel balls have hardness and also “roundess” value. There is no perfect sphere. The “G” number, which goes from 3 to 2000, denotes how perfect the sphere is. a G3 steel ball means, it has only 3/1000 inch of deviation from “perfect” sphere. Anything under G100 steel balls are made to order, so I don’t expect to find them at my regular bearings store. So, what is the minimum perfect G value to get? I don’t know! 3/16 inch is a common size for Shimano hubs, and its about ~1.9mm. Let’s say 2mm: a G3 grade 3/16 steel ball have a tolerance of 0.0008mm, roughly(!), while a G1000 grade is, 0.025mm. There is no caliper available to measure these, even micrometers will fail. They are magnetically measured, with very complex machinery. I believe the worst grade will do, but even cannot be sure that I can get these from a store; as far as I know, no big brands, such as SKF, sells steel balls only.
I think the hardness is an important factor on longevity: these balls must be soft enough to roll without digging into cups and cones in long run, and hard enough to not deform. Given that most bikes are rated for 120kg, this shouldn’t be a huge problem. Most steel balls are rated having Rockwell hardness of 40-65.
Well, I think what matters most is, material, especially corrosion resistance. Silicon Nitride is absolute best, ticking all the boxes, such as corrosion resistance, hardness and fatigue life. They are crazy expensive: expect to pay around 20$ for a single 3/16 ball, G20 grade! Guess what it is? It’s “ceramic”. Actually, most people think ceramic bearings are white. White ones are Zirconium Dioxide, while blued steel look Silicon Nitride is even better, and a bit more expensive. Campagnolo uses them (CULT bearings) in caged form on some highest end components – so they can save a few, miniature but crazy expensive balls with this design.
So what to do about it? I know a good store that sells nice bearings, and tell them “give me the best you got” – I buy them bulk, like 200-300grs at a time (they sell steel balls this way, at least here) and replace balls whenever I service the hubs or pedals.
SKF MTRX bearings can be a great news for bikes, but we’ll have to wait.
SKF MTRX Bearings
SKF seems to show great interest on bikes: they produce high-end square taper bottom brackets, and now they come up with MTRX bearings.
MTRX bearings looks like ordinary cartridge bearings with one huge difference: an oil filled polymer fills the gap between the race and the balls. It’s much like a 2RS bearing sealed on both sides, but the seal itself is the lubricator, in this case, because its soaked with some special oil. This looks like a great idea. SKF says MTRX bearings are immune to even pressurised water.
I never tried SKF’s bottom brackets or these MTRX bearings myself, but at least I know 2 things: SKF makes great bearings and they’ re into bikes (and cars). They’re not cheap: smallest cartridge bearing of the series, SKF 608 2RS1, is nearly 15$, which is more expensive than most of my pedals. (Note the 2RS1 designation, instead of 2RS). If they live up to their expectations, it is a worthwhile investment; otherwise lots of cash thrown into trash. I’d still like to try them some time, but they’ re not available in my country. It’s nice to see they are also producing seal kits for suspension.
What they don’t tell you about seals in cartridge bearings
Reading about “bike technology” drives me nuts. There are really exceptionally few people know what they talk about. Like “sealed cartridge bearings provide long life” etc.
Seals in cartridge bearings on a bike DO NOTHING. In fact, if just adds to friction. Seals in cartridge bearings, like the ones you see at 2RS bearings, is there to keep grease in, and not let air in! They’ re totally helpless when it comes to water. That’s why so called “sealed bottom brackets” don’t last long, because they’ re not sealed, and you don’t know that. If you knew they’ re not sealed at all, probably you would fit fenders, even chain guards as in vintage bikes.
I had a marine engine repair shop. You know what? There are no “sealed” bearings in a marine engine; because engineers are smart enough to know they never work. Instead, they have proper labyrinth seals where there is water contact.
All the outboard bearing bottom bracket design I saw so far is not water sealed, including Campagnolo. They are consumable parts, and most of them only last long as disc brake pads.
There are many headset standards. Contrary to popular belief, not all 1 1/8, Ahead (threadless) headsets, thus the bearings, are the same!
I don’t want to go into every detail, because headsets deserve a post on its own. Still, you must know that you need to know a few details to shop for correct bearing.
Exotics and old 1″ threaded forks aside, head tubes have inner diameters of 30mm, 34mm, 44mm, 49mm, 56mm, even 62mm. So, first of all, when buying a new complete headset, make sure races will fit. This is the first number to look for.
Then, you have to determine if your headtube is “oversize” – standard, new 1 1/8 threadless forks are 28.4mm in diameter, but recent ones are 1.5″ or 1.4″ at bottom end. That means, races that goes into headtubes are different. Top crown still has 28.4mm (1 1/8 inch) but bottom ones are 1.5 or 1.4 inch. There are also conversion kits.
Once we press over cups, we have to know which bearing goes into them (if you buy them as a kit, you don’t need to worry as they come with bearings) Now what? It’s getting even more complicated here! Top cover and bottom crown race complicates matters, again: these 2 parts sits between your fork and bearings, and have different sizes. And some brands like Specialized or Cannondale use “proprietary” headtubes. Are we done? No! Lets say you get the correct size cartridge bearings with inner and outer diameter. It may still don’t fit, because of chamfer angle.
Oh, I didn’t mention some headtubes accepts integrated bearings, without cups.
These parameters together makes it almost impossible to get the correct bearing; so people tend to buy a whole set.
Lately, I’m pissed of with this, and bought a Neco headset for 1 1/8 tubes with caged bearings. I ditched the caged bearings, and put some nice, shiny ball bearings instead. Works perfect, cheap to maintain, and I always know what to buy. I usually run on narrow tires and without suspension, so cartridge bearings do not last. Luckily, races are pretty solid.
Bottom bracket bearings
For square taper bottom brackets, almost each brand and model uses different bearings, either one or both sides using non-standard (AKA expensive or non-existent) cartridge bearings. So, either look for a bottom bracket with standard cartridge bearings (good luck!) or replace the whole bottom bracket.
Good news is, there are also “cup and cone” style square taper bottom brackets. You know what? My wife’s 10 year old, supermarket bike with lowest-end parts crankset is much more fluid then my Deore XT’s or SRAM GXP’s. They have cup and cone, square taper bottom brackets. They are not sealed. Caged bearings are horrible quality. But if you buy a nice, sealed set, and know to adjust tension on them, they’ll serve you forever.
No one bothers to develop better cup and cone square tapers anymore, the longest surviving and world’s most common bottom bracket standard. If they are good for hubs, why not for bottom brackets? Yes; they’ re heavy, but anyone seen a larger diameter, hollow titanium axle? Or nice, “ceramic” bearing balls? Rene Herse at least, makes great square taper cranksets weighing in low 500-grs. If you have a beater bike, get cup and cone style square tapers, and maintain them regularly. They’ll last forever.
For 2-piece cranks, where the bearings sit on external cups, it’s a different story. These bottom brackets use tiny cartridge bearings which is a bad joke. I lately bought a genuine, SRAM GXP bottom bracket and started creaking a bit after 300-400 km’s. Shimano’s Hollowtech lasts a bit longer. GXP uses standard bearings on one side, which is perfect, and uses non-standard bearing on other side, which is bad. Even all bearings standard, cartridge bearings of good quality is expensive, and won’t last long given the design of the cups. Unfortunately, bottom brackets are consumables like brake pads.
I’d like to have pedals with ball bearings. Do not buy pedals with cartridge bearings: bearings in them are extremely tiny, and won’t last long. Most of them comes with garbage cartridge bearings. Good pedals have very high quality steel spindles, and ball bearings do not damage them. They are very easy to maintain.
Jockey wheel bearings
If you have jockey wheels with cartridge bearings, do not bother to change them. Get ones with proper bushings instead. They roll like fidget spinners when they’ re out of the box, and give up at first heavy rain. Replacing them is painful, won’t worth the hassle and not to mention, those bearings are hard to find and not cheap.
General bearing shopping advice
Bikes have size limitations, so it’s not easy to use different sized bearings, even if you have a lathe and CNC milling machine. So you’re stuck with what you have: you cannot convert cup and cone hubs to cartridge bearings, or vice versa, in majority of cases.
So, being sensible first is important: I wouldn’t use a Hollowtech II or GXP crankset for a beater bike. On the other hand, I’m damn happy with cup and cone hubs and pedals, because they’ re cheap and relatively easy to service. You can change cups on some models, too. But for a beater bike, I think cartridge bearings are better: cup and cone bearings have generally proprietary seals, so if they swell, worn or tore apart, your hubs are paperweight. On cartridge bearing hubs, changing the bearings pretty much “resets” the whole hub.
If you want total serviceability with minimal expense, get Shimano hubs, at least Deore, or SLX. XT and XTR have plastic caged bearings on one side, which are expensive. It’s nice to have same size loose ball bearings on each side, and each end (front and rear). You’ll probably need smaller ones for trusty cup and cone style pedals. So, if you can live with cup and cone style square taper bottom brackets, loose ball bearings headset, pedals and hubs, you’ll probably need 2 or 3 different size ball bearings. This is super cost effective. Ball bearings are dirt cheap, easy to stock, and do not need special tools like pullers to replace.