Angular vs Radial loads - bottom brackets - mechanical engineers where are you?

Triathlon Forum
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I’ve been interested in learning more about bottom brackets. I have an Enduro Bearings BSA30 ceramic bottom bracket and their Zero Gr3 ceramic pulleys. I used to have the Enduro Bearings XD-15 before I got a BB30 Quarq that I needed to use on my GXP P2. Please don’t get into the argument of ceramic vs stainless steel bearings. I have the Friction Facts reports and I’ve seen the data. I was reading this link here http://www.slowtwitch.com/…_Breakdown_2822.html

and have googled alot of stuff as well as talking with an Enduro employee over email.

How does someone create a lateral load on a bottom bracket? Angular bearings help to solve the problem of radial/lateral loads is what I have read.

Does the load come from cornering on a bike or swaying the bike side to side when sprinting or climbing? Since the crank doesn’t move side to side and is rotating in a circle, where does the lateral loads come from?

Maybe I should have payed more attention in physics during my engineering undergrad haha. Thanks for the help. Maybe someone else will find this useful

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It seems difficult to explain this without sounding tautalogical, but lateral loads are the result of lateral forces that are resisted by constraints in motion.

If you can imagine riding an unbolted crankset, each side held independently by just a pin with no lateral constraint - any pedalling motion that would pull out of the frame would have resulted in lateral loading on a normal installation. If you also imagine having to maintain an offest to the frame, then any motion that moves closer to the frame would have applied some lateral loading.

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How does someone create a lateral load on a bottom bracket? Angular bearings help to solve the problem of radial/lateral loads is what I have read.

Does the load come from cornering on a bike or swaying the bike side to side when sprinting or climbing? Since the crank doesn’t move side to side and is rotating in a circle, where does the lateral loads come from? Every time you try and apply a vertical/tangential force to the pedals it will be off that ideal axis and therefore have a lateral force component.

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Maybe I should have payed more attention in physics during my engineering undergrad haha.

This?

It’s a simple vector mechanics situation. Because the pedal force is offset from the reaction at the bearings, the bearings are under a moment and need axial forces to resist it. Also the bearings are preloaded so there will be a small axial force there too.

In practice though, the axial force must be pretty minimal since the radial bearings work just fine.

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[quote BryanD
Maybe I should have payed more attention in physics during my engineering undergrad haha. Thanks for the help. Maybe someone else will find this useful

Your dynamics professor isn’t mad at you, he’s more hurt deep down inside; he’s crying right now.

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ouch! tough crowd here. I actually did much better in the electrical side of physics. That’s probably why I have electrical and computer engineering degrees haha.

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Maybe I should have payed more attention in physics during my engineering undergrad haha.

This?

It’s a simple vector mechanics situation. Because the pedal force is offset from the reaction at the bearings, the bearings are under a moment and need axial forces to resist it. Also the bearings are preloaded so there will be a small axial force there too.

In practice though, the axial force must be pretty minimal since the radial bearings work just fine.

Agreed, axial force is minimal. A typical radial bearing race (i.e. groove that balls roll in) do have some ability to resist lateral loads. For cycling, I also suspect due to historical performance that forces are extremely small vs. bearing performance.

However, if designing a bearing in industry (read a lot more hp than a human), then attention to these lateral forces is important. The bearings for your cars front tires for example. When you are turning and going around corners, there can be substantial lateral forces going on due to dynamics.

Cycling has very light weight components and powered by a pitiful engine (youtube cyclist vs. toaster), and you will get an appreciation of what type of power we use during our everyday tasks.

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How does someone create a lateral load on a bottom bracket? Angular bearings help to solve the problem of radial/lateral loads is what I have read.

The biggest lateral loads are caused by preloading and misalignment. Angular bearings tolerate both better than radial.

But radial bearings will take the small lateral load that happens in hubs and BBs due to regular cycling (standing is typically the highest) without issue. And radial bearings have less drag when the loads are radial.

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Wouldn’t angular bearings take cycling loads better due to all of the balls making contact on the races?

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I think the only way all the balls will make contact under radial loads is when they are axially preloaded quite a lot. That isn’t a good thing. The drag is least when there is no preload.

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youtube cyclist vs. toaster

That video is awesome! The legs on that guy are bananas!

Since installing a power meter on my bike, every time I have pasta for dinner I find myself wondering if I could generate enough power to boil the water… now I think almost certainly not.

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youtube cyclist vs. toaster

That video is awesome! The legs on that guy are bananas!

Since installing a power meter on my bike, every time I have pasta for dinner I find myself wondering if I could generate enough power to boil the water… now I think almost certainly not.

Glad you enjoyed vid : )

Boiling enough water to make pasta?! No way. 1 cal. will raise 1cc of water 1 deg. C.

Off the cuff here… 100 C - 25 = 75 C (assume 2 liter of H20 = 2000 cc), that’s 150,000 calories! (assuming all energy goes into heating the water with no loss to atm. (totally not ideal).

We (myself included) use electricity all the time without a second thought on what it takes to drive an AC unit, boil water, or even heat water for our house.

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150,000 Cal or 150 kCal or ~630 kJ, an easy ride.

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150,000 Cal or 150 kCal or ~630 kJ, an easy ride.

Excellent,

Please upload your video of you bringing 2 liters of water to a boil using a bicycle.

I will ‘like it’ for sure.

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https://www.youtube.com/watch?v=fgHJlTCsJZw

Not mine, obviously, but I get a surprising number of hits when I do a search for “boiling water human power.”
.

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This reminded me of this clip I saw on bbc awhile ago, had to go look it up.

http://news.bbc.co.uk/2/hi/science/nature/8394055.stm

Apparently it takes ~80 cyclists to power a house.
.

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https://www.youtube.com/watch?v=fgHJlTCsJZw

Not mine, obviously, but I get a surprising number of hits when I do a search for “boiling water human power.”

From their data, I get a little difference of about 63,375 J (still close) when convert it to the 2L calc.

Also interesting is that he started with 3 cups and ended up with 1 cup of water. I figure this is due to it taking 30 min. to reach temp.

So the energy to boil water is more of a diff-equ. in real world application due to the water volume reducing by 2/3 over 30 min. Would make for some starchy pasta.

Thanks for sharing : )

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I know, math is hard.

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Glad you enjoyed vid : )

Boiling enough water to make pasta?! No way. 1 cal. will raise 1cc of water 1 deg. C.

Off the cuff here… 100 C - 25 = 75 C (assume 2 liter of H20 = 2000 cc), that’s 150,000 calories! (assuming all energy goes into heating the water with no loss to atm. (totally not ideal).

We (myself included) use electricity all the time without a second thought on what it takes to drive an AC unit, boil water, or even heat water for our house.

I’ve never bothered to do the calculation, just thought about it.

Your calculation looks good, except that’s 150,000 calories with a little ‘c’. That’s only 150 Calories with a big ‘C’ (or kcal) as reported on food nutrition labels.

So actually, I think bringing water to 100C is doable depending on how much energy you loose to the environment and equipment. Taking your starting point of 2L of room temp water at 1 g/mL density and an average energy of 4.19 J /(g * C) (this is equivalent to the mean calorie), the energy required to raise the water temp to 100 degrees C is:

(100C - 25C) * (4.19 J/(g*C)) * (2000 mL) * (1 g/mL) = 628.5 kJ

If you assume an average output power of 250W, then it would take (628.5kJ) / (250W) = 41.67 minutes to bring the pot of water up to 100C. Not a bad ride.

But, this only gets the water up to 100 C. It isn’t actually boiling at this point, you still have to overcome the enthalpy of vaporization to get a boil. For that you have to add an additional 4,520 kJ! And at 250W this would take 5 hours!

As you pointed out this neglects heat lost to the environment, whatever mechanism you’re using to convert the bike’s mechanical energy into thermal energy.

So I guess the result is the same: not feasible.

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Can we get this thread back on topic?

I’ve read a lot about the different bearing designs. It seems that radial is great because you don’t have to set a preload, but angular handles radial and angular loads better.

Thoughts?