Everything You Need To Know About Bearings | Hambini Engineering Special

Everything You Need To Know About Bearings | Hambini Engineering Special


Welcome to a special episode here
on the GCN Tech channel because I’m joined by a legend in the
world of bearings or it certainly is for me and I reckon by the end of this episode,
he’s going to be a legend for you too. Welcome, Hambini.
-Thanks very much for the introduction. I think you might have been a bit over the top
but I’ll give him my best show. Cool, okay. Hambini himself
is actually an engineer by trade so he certainly slightly more qualified
than myself to talk about bearings this size. Well, you’ve submitted your questions
for us to answer, so we’re going to do just that. Now, one of the most common questions we get
actually is what’s the difference between the low-end bearing and a high-end
bearing in terms of drag or resistance when riding along
and I’m pretty keen to know this because I love the marginal gain
hearing that, so hit me with the stats. If you get a bearing this typically no name
versus something that’s named and isn’t a fake, the typical drag for everything
so that’s your bottom bracket and freewheel, the hubs, the jockey wheels is about
somewhere between 7 and 10 watts. Okay. Well, that’s up to me.
-It does. The vast majority of the drag
comes from the seal. It’s nothing to do with the bearing material
whether you buy ceramic or steel. It’s almost irrelevant. The vast majority
comes from the seal and if it’s contacting. The next proportion of the drag
is from the lubricant you use. If you use like a thin oil which
is less viscous, you’ll have less drag. The problem with doing that is you will
have to maintain it more frequently. Some of the top cyclists,
I think it was Alberto Contador, he used to take all the seals off
and put in a drop of mineral oil. That’s what his mechanic used to do to reduce
the drag to the absolute bare minimum. What’s the difference between
a cartridge bearing which is what these types of bearings
are commonly known as in the bike world up against a cup and cones style bearing?
A cup and cones style bearing is what– Well, traditionally, in the bike trade,
we used to use for– well, forever until the invention
of these bad boys. Yes, a cup and cone bearing is in effect and angular contact bearing
that is constrained. An angular contact bearing
that we’ve sliced in half- -That’s so cool.
-is one of these. Yes.
-What we’ve done is I’ve tried to draw them pretty poorly, try and draw pretty poorly and a section
through it and that’s what you see here. At the same time, this type which is what’s
commonly known as a cartridge bearing– Again, I’m drawing a section through here
or describe what the difference is. The first obvious one is when you look
at that one, it’s symmetrical through the axis, so you can go both ways, looks the same.
This one, the angular contact is not. One side is the cup which is this side Yes, that’s better in it. The cup is the inner race and the cone
is the outer race. Now, unfortunately, in order to do this little prop,
I have to weld in there. That’s a small bit of metal,
it shouldn’t be there. If you show them that piece,
you can see the shape is not symmetrical. What happens is on the cartridge bearing, because it’s symmetrical,
it takes a load in either direction. You can run it in either way and
a lot of manufacturers use that ability. Notably SRAM with its GXP bottom bracket. One bearing is fixed
and it takes a load both ways whether you’re pedaling
with your right foot or your left foot. All the axial load is going through
the non-drive side bearing. The turning load which is called the radial
load is being transferred on both, but the axial is just one on side.
When you look at the angular contact bearing, the ball for the same outside diameter
is bigger. The contact angle which is called
the alpha angle, which is this angle here, some bearing manufacturers put
the angle slightly differently, but I’m drawing like this for consistency, is much further towards an axial direction
than the cartridge bearing. The cartridge bearing is designed to take
radial load and not much axial. The angular contact
will take a lot of axial seeds. This is called the load center
where the two lines cross. If you had the bottom half of the bearing
and drew it across, you would have a load center and be offset
by X millimeters, maybe 20 or 30. The actual load carrying capabilities
significantly more. The original question was, what was
the difference between cup and a cone. A cup and cone is an angular contact bearing.
It’s just unconstrained. A cup and cone doesn’t have
the metal cage holding the bowls and in place as the true angular contact does. How’d you know what size bearing you need
for those DIY replacements at home? The best way to do it is to take it out
and measure it. If you can’t do that and you’ve just got
the numbers on the outside to go off, you can decide on the bearings. Once again, easiest job is to go into Google
and just type the number in, it’ll give you it. For interest’s sake,
I’ll go through it on this board. The first number on a four-digit bearing
will typically be a six or a seven. A six is a deep groove ball bearing, seven is angular contact. The second number is in effect
the outside diameter of the bearing. It doesn’t follow any particular coding. It just goes from 7, 8, 9, 0, 1, 2 and so on.
That’s just getting bigger. The 06 is the ball. Balls will go 00 which
is 10 mm. 01 which is 12, 02 is 15, 03 is 17, 04 is 20. When you get to 04,
all of the subsequent numbers, you just multiply by five. 05 is 25 and 06 is 30. From this, the BB30 bearing is six
which is deep groove ball bearing. The eight is just the second number
in the outside diameter series and it’s 30 mm ball, so it’s 30 X 42 X 7. This is not something off of a tank bang
because you’ve gone through that so fast. All I’m thinking is, “Hey, it doesn’t really make
any sense.” I’m not going to worry about that because I think for most people out there,
they’re not really going to look into that, in too much detail, are you? If you can look at the side of the bearing
on there for those numbers, basically, and that’s what you’re going to be looking for. How do you tell when a bearing is worn and when
is the best time to replace it if you can’t tell? From my own experience
or knowledge about bearings, at least if you were to cut it away like this,
you can see when you’re turning it, the different parts of the bearing
are moving at different speeds which I guess means they’re wearing
at a different rate. As Jon’s turning the inner race, this bit which
obviously, this is not a complete bearing. As the speed to that rotator
is called the inner race frequency. If you were to take a bottom bracket example,
typically, some people are going to pedal it. To make the numbers easy, let’s say, 60 RPM.
The reason I picked 60 is because it’s a minute. In a minute, you’re going to go 60 times. The inner race travels at a certain speed
and gives you a frequency. The balls, these things will turn
at a certain frequency. The whole thing is turning on
the fundamental train frequencies. The fundamental train frequency
is the rate that effectively the cage is going around them.
The cage rate is slower than the inner race. You’ve also got ball-spin frequencies
on the inner race and ball-spin frequencies on the outer race. There’s quite a lot of frequencies in there. Inevitably, the failure mode
on a bicycle bearing is usually from an external factor
such as contamination. You get a bit of grit in there,
the ball spins around and then grinds itself
into one of the races. That’s how that fails. If you are going to regrease your bearings, what sort of grease should you use
and how much? Because certainly when I used
to regrease cup and cone bearing, headsets that sort of thing, I would pack
as much grease in there as possible. Probably to make the job a little bit easier
of loading all those bearings and making they didn’t fall out around
on my mom’s best carpet or something like that which I got
in trouble for. Any tips or advice there. Bearing manufacturers, the big ones, ?SKF. Those people, they’ll give you guidance
as to how much grease to put it. Typically, it’s a third.
A third of the total volume should be greased. Say, this bearing here.
I’ve gone ahead, I’ve decreased it, tried to air because I will use some air,
glass over there. I’ve even used a hairdryer it before
that just to get it perfectly dry. Hopefully, that’s all right to do.
-Yes. Okay, good. Not going to get told off that one.
I should go, say, a third of the way round, should then just spin it to get it in there
just a little bit more? It’s a third of the total volume.
-Okay, right. You don’t necessarily need to go a third of the
clock face, just a third of the total volume. Just to spread it out evenly
but just at third. If you overfill it, what happens is the balls won’t be able
to move very well so you’ll have more friction. The aim of the grease is, as the thing warms up,
it actually turns to oil. It goes soft and becomes more of a lubricant
and that’s what you’re rolling in. What sort of grease am I going to put in there? General guidance is lithium grease.
It is based on a scale, the grease type, of NLGI and something like a one on that scale,
would be the one to go for. It doesn’t really mean a lot to me
but I guess if you’re really into it, you could have a little look and research it. Have it on a data sheet and it’ll tell you. Now, I have to say, you mentioned earlier on
about it when the grease turns into a liquid when it gets up to a certain temperature,
that sort of thing. I recall I think it was either
Fabian Cancellara or Alberto Contador who we’ve already spoken about, the
roof seals, and bearings, that kind of thing. I have this weird feeling
that one of them had a guy at the side of the mechanics truck
who used to spin wheels before he raced in time trials
to get that lubricant turning into a liquid. Just getting the grease into a liquid. Is that going to give you,
do you reckon, hypothetically speaking, significantly better or less wrong
resistance in the bearing or not? It’s going to be so marginal, isn’t it? For the first few kilometers, probably.
The thing is, at their level, the difference between winning or losing
is that sort of attention to detail. If you’re just out smashing it on the weekends,
then it doesn’t matter. Yes, we’re not going to be like Formula 1 pits,
are we? We warm up the tires. I can’t imagine you sat in your garage,
me sat in mine before we go out, spinning our wheels to make sure that the bearings or maybe you do. No.
-Okay, that’s good. I don’t even wash my bike.
-Another cracker of a question here. Andrew Montgomery,
do ceramic bearings last forever? Thing with ceramic bearings on a bike is, they are technically
or the vast majority of them are hybrid. The balls in them are silicon nitride
or something along that lines. They’re very hard material
but the races aren’t. They just generally tend to be steel.
If you have a very hard material rubbing against a relatively soft material,
what happens is, it wears a track inside the bearing. While the balls don’t fail,
the track that it develops, does. It would be akin to getting a locomotive
and running on a road. The rails are significantly harder than
the tarmac so it would cut a hole in it. What you want is materials
that have a hardness that’s much nearer to each other
and they will last longer. Okay, so that’s the thing. A lot of people out there
and I’ve fallen victim to this in the past you see a ceramic bearing offered really,
really cheaply and you think, “I’ll get that.” It’s like £2 or something. Crazy low price. Ultimately, that is not going to last, is it?
I think we can safely say that. There’s a couple of things
with bearings as a whole, not just specifically ceramic. One is fakes. There are a lot of fake bearings on the market. You wouldn’t believe how much have crossed
my desk and the desks of my colleagues. In that sort of size,
so we’re not talking small bearings. That’s baffled me really because
I’ve never seen a bearing this size– well, I probably have but in the back of some big
machine or something like that in a factory. I wouldn’t have thought that someone would
be making fakes for that. I would have thought– because I’m, I supposed, obsessed with bikes, I would have thought,
“They only make fake bearings for bikes.” The fake bearing for a bike is probably
only going to cost £2, $3, €4, whatever the currency is
but one of these bearings costs a lot. If you can fake one of these, then the margin
that they get is significantly greater. In terms of the bike,
when you buy the fake bearing, what you’re getting is a bearing
that doesn’t have the dimensional accuracy. What they rely on is people
not having the instrumentation and the measuring gear to be able to tell
that the bearing is not quite right. Now, one of the most common questions
actually you see on the internet is someone who says,
“I’ve had a bottom bracket for 2,000 kilometers and it’s already worn out,” and then someone else will have exactly
the same bottom bracket and they’ll say, “Well, I’ve been riding for five years
that bottom bracket and it’s still in perfect condition.”
We’ve got a graph. What’s this graph all about? One of the things that you have
in engineering principles is load versus life and that’s
typically called an S-N curve, but I’ve simplified it here
for the benefit of the viewers. Load is along the y-axis and cycles is along
the x-axis. The x-axis is a logarithmic axis. It’s going up in multiples of 10. It’s not
linear 10. We’ve got 10, 100, 1,000, 10,000 and so on. If you are pedaling with a very,
very low cadence but massive torque, you’re putting a lot of load
into those bottom bracket bearings. You’re be over here. You actually get less life
than someone who spun their cranks up and was putting less load,
but more RPM through. The limiting factor on a bike is not the speed
because it’s whether it’s 60 RPM or 100 RPM, that’s nowhere near the limit of the bearing, but the torque
that you put through the bearing is. That differential is. The person who
is only getting 2,000 kilometers if they are on the heavy side,
then they’ll be that way. The person who’s lightweight
and spinning at 120, they’re putting significantly less
torque rate so they’ll get more cycles and it’s just the way it is. You got like a track sprinter.
They’re going to be– Well, somewhere around here, aren’t they?
-Yes. You’re climber, you’re real lightweight rider,
they’re going to be– Well, hopefully, if they’re spinning,
away they’re going to be somewhere, hopefully, down there, aren’t they?
-Yes. Now, finally then,
what about maintenance of bearings because not everyone likes to get
their hands dirty and grubby like, “That’s in the workshop,” do they? What can the viewers do to try and
get longer life basically on their bearings? There’s a few things.
The biggest one is contamination. Contamination will make the life
of the bearing shorter, that’s the biggest one. The other one is when you come to install it,
when you install bearings, you tend to have a press
that presses directly onto the bearing like a BB30 press or something like that. One thing that people start aspire to
because I think it’s good, is having stainless steel presses. Stainless steel is a pretty terrible
material in some characteristics. It has this characteristic calling, it goals. That’s when it friction welds itself
to another material while the friction welds itself.
You can have an issue where you put the bearing in
and as you’re tightening the press, it goals on the surface, so it’s trashing
your bearing before you even get started. I’d recommend you use either plastic
or aluminum or if you are going to use a stainless steel, make sure it’s got a bigger clearance
than you would normally have. Another thing is when you’re pushing
putting the bearings in, the most common failure mode I’ve seen
is poor alignment. Alignment specifically embossed
and brackets because unlike wheels which tend to be machined on
the lathe bottom bracket is quite a lot, a lot of time on carbon bike frames
are glued together in the middle. What happens is you’ve got two bearings
and they’re slightly misaligned. If you take these two as an example, you might
have, what’s known as parallel misalignment. If the right hand is the drive side of the bike and the left-hand side is the non-drive side,
that’s parallel misalignment. They’re completely offset
or you can have angular misalignment so the center lines are in the same place
and won’t tip. If you have any of those things
and you’ve got moving parts in there, then what the crank tries to do
is it tries to straighten itself. It can only straighten itself
through the bearings because that’s the only point of motion and you’ll tend to do that which
you called fretting. Bearing is really, really hard. Carbon isn’t. It’ll just wear the whole out.
You need to worry about that. In terms of routine maintenance, I personally don’t take the seals off
to repack the grease. I just change the bearing. Do you think the life’s gone, basically?
-Life’s gone. Plenty of people take the seals off
to grease them. I certainly won’t recommend
knocking them out. Guilty. A massive thanks to Hambini today
for popping in and telling us all about bearings
and all sorts of graphs and some of that. I’ve learned a hell of a lot today
and I hope you have too. After all, if he wasn’t here,
I wouldn’t have had some of these. How cool is that? Now, remember as well
to like and share this video. Give it a big thumbs up.
Tell your friends about it especially if they’ve got bearings
are absolutely knackered and you need to just reaffirm the point,
they’ve got to replace them. Also, remember to check out the GCN shop at
shop.globalcyclingnetwork.com. We have a whole heap of products for you
to check out. What video should they watch now? Maybe they should watch you
pressing in a bottom bracket. Hopefully, I did that one right. I’m pretty sure
I did. It’s going to be just here.