freehub engagement?

[eddief]

i think i get the idea of angle of engagement being primarily related number of ratchet teeth but what is the value of the number of pawls. if you have two wheels where the ratchet has the same number of teeth but one has 3 pawls and the other has 6...is something better about one over the other?

even though maybe not the most secure would the mechanics be the same if the hub had a single pawl?

[bikinchris]

If it had a single pawl, it would twist the freehub body on engagement and it would fail faster.

[m_sasso]

Was that a 4 cylinder or a V8?

[Old School]

Your minimum pawls need to be three, otherwise the hub will go off center (three points define a plane)

A hub can have three pawls doing work at one time, and then another three pawls (six in total) doing work offset from the other three.

So three clicking 24 times per revolution, and than another three clicking at a different 24 times per revolution, will give you 48 engagement points.

[m_sasso]

Your minimum pawls need to be three, otherwise the hub will go off center (three points define a plane)

Incorrect, plenty of two pawl freehubs.

More about pawls https://www.dtswiss.com/en/technology/wheel-technology/pawl-technology/


https://images.worldwidecyclery.com/s/files/1/0349/7357/products/HU2144_x1024.jpg?v=1574288726

https://r2-bike.com/media/image/product/127851/md/extralite-freehub-body-conversion-kit-shimano-version-10-for-ultrarear-sx-spx-slx-hub~2.jpg

[eddief]

that my 185 lbs stands up on the pedals and all that power is transferred to the rear wheel through those tiny little pawl things. bikes ARE cool.

[Old School]

Incorrect, plenty of two pawl freehubs.



I never said there was no such thing, I just said "Your minimum pawls need to be three, otherwise the hub will go off center "

I won't ride a two pawl hub. They bother me.

[Louis]

that my 185 lbs stands up on the pedals and all that power is transferred to the rear wheel through those tiny little pawl things. bikes ARE cool.

The pawls themselves are mostly in compression, so no significant tensile stress.

Plus, little = no big bending stress

[happycampyer]

This is why I find the Onyx sprag clutch so cool.

https://www.youtube.com/watch?v=en1HhxKwdJo&app=desktop

[eddief]

what does that mean to liberal arts majors?

The pawls themselves are mostly in compression, so no significant tensile stress.

Plus, little = no big bending stress

[Veloo]

I opened up a set of lower end Mavics a few years ago to find only 2 pawls. Don't remember the model - either Cosmic Elite or Aksium.
I mentioned to my wrench and he said all their freehubs are 2 pawls.

[glepore]

The gospel according to pawl. More better.

[Mark McM]

I never said there was no such thing, I just said "Your minimum pawls need to be three, otherwise the hub will go off center "

I won't ride a two pawl hub. They bother me.

Then I guess you won't ride a Shimano freehub, because most of those were 2 pawl.

https://www.parktool.com/assets/img/repairhelp/freehubparts.jpg


And going back even further, most freewheels were 2 pawl as well.

https://www.sheldonbrown.com/images/IMG_0081-pawl.JPG


It is the bearings that keep freehubs (and freewheels) on center, not the pawls. The pawls just carry torque loads.

[m_sasso]

I never said there was no such thing, I just said "Your minimum pawls need to be three, otherwise the hub will go off center "

I won't ride a two pawl hub. They bother me.

Sorry, you are still incorrect, there is nothing inherent in the design of a two pawl hub compared to a three pawl hub that will cause a free hub to "go off centre".

The two previously pictured two pawl free hubs, one produced by Hope and the other Extralite are both quality manufactures and every builder from Mavic to Sturmey Archer has used a two pawl design. The number of pawls contributes little to nothing in keeping the free hub centered about an axel in a wheel hub.

Sorry, accept my apologies, no disrespect, however people who don't know what they are communicating about and spew fiction, bother me.

[bikinchris]

Then I guess you won't ride a Shimano freehub, because most of those were 2 pawl.

https://www.parktool.com/assets/img/repairhelp/freehubparts.jpg


And going back even further, most freewheels were 2 pawl as well.

https://www.sheldonbrown.com/images/IMG_0081-pawl.JPG


It is the bearings that keep freehubs (and freewheels) on center, not the pawls. The pawls just carry torque loads.

That's why many tandem riders were very particular about what freewheel they would use,

[Louis]

what does that mean to liberal arts majors?

If we're talking simple stuff, there are two types of stress, uniaxial (aka normal) stress and shear stress. Uniaxial stress can be either tensile (pulls things apart) or compressive (mashes things together). It's very hard to break something that's in compression, either due to static overload or in fatigue. It's easier to do it in tension, either due to a small number of very high loads, or, in the case of fatigue, a high number of lower loads. Lots of the time you get high tensile stresses from bending, not just simple tension. Shear stress can also be important, even in a case where you have compression.

I'm not sure what would cause the highest failure-inducing stresses in a pawl, possibly shear, but there are also plenty of local contact-related stresses that could be a problem.

Wiki provides some good info here:

https://en.wikipedia.org/wiki/Stress_(mechanics)#Simple_stress

https://www.fictiv.com/hwg/sites/default/files/inline-images/strength%20vs.%20stiffness-image03.png

[oldpotatoe]

Your minimum pawls need to be three, otherwise the hub will go off center (three points define a plane)

A hub can have three pawls doing work at one time, and then another three pawls (six in total) doing work offset from the other three.

So three clicking 24 times per revolution, and than another three clicking at a different 24 times per revolution, will give you 48 engagement points.

Not exactly....shimano and mavic wheels and hubs were 2 pawl for decades..
I wouldn't be surprised current shimano freehub bodies for their wheels and hubs are 2 pawl today(not sure, haven't opened one up in a while).
99.9% of the freewheels made were 2 pawl(Campagnolo were 3 pawl, probably others).

[coachboyd]

Not exactly....shimano and mavic wheels and hubs were 2 pawl for decades..


This is also when most people were riding a 23tooth for their easiest gear. As derailleurs have gotten better and can accomodate larger cogs in the back, the potential for torque load on a rear wheel goes up. Things like number of engagement points, number of pints of contact, and engagement speed can all affect how the hub internals hold up to torque demands. Slow speed, easy gear, and high power output from a low cadence puts the most torque on a rear wheel.

Give a mountain biker a 2 pawl rear hub and they'll probably destroy it in the first hour of their ride. Planning the driver around the torque loads that the hub will see (whether it be road, gravel, or MTB) is key.

[Mark McM]

This is also when most people were riding a 23tooth for their easiest gear. As derailleurs have gotten better and can accomodate larger cogs in the back, the potential for torque load on a rear wheel goes up. Things like number of engagement points, number of pints of contact, and engagement speed can all affect how the hub internals hold up to torque demands. Slow speed, easy gear, and high power output from a low cadence puts the most torque on a rear wheel.

Give a mountain biker a 2 pawl rear hub and they'll probably destroy it in the first hour of their ride. Planning the driver around the torque loads that the hub will see (whether it be road, gravel, or MTB) is key.

Mountain bikers have used (and are probably still using) 2 pawl freehubs without any problem.

If you take a look at the Shimano freehub disassembly drawing, you'll notice that the pawls are huge - about twice as wide as the pawls on many 3, 4 or 6 pawl freehubs. One big difference with Shimano freehub pawls (and also the earlier freewheel pawls) is that they are located within the freehub body (between the freehub bearings), where there is lots of width for the pawls, allowing lots of pawl/ratchet tooth contact area. With the advent of oversized (aluminum) axles, there is no longer room inside the freehub body for the pawls, so the pawls are moved to a narrow space between the freehub and the hubshell. This narrow space allows only narrow pawls. In order to increase total pawl/ratchet tooth contact area, more pawls have to be added.