Talk about torque on the rear freehub.

[GuyBoden]

I'm slightly concerned that having these modern large rear sprockets (46t+) on a roadbike freehub is creating too much torque for some freehub internal ratchet and pawl designs.

I've changed over to using Hope freehubs, that are based on mtb design and seem a stronger design.

So, lets talk about torque concerning freehubs with large rear sprockets. What do you think?

 

[Ming the Merciless]

It'll come down to the gear ratios

A 30 / 50 gear ratio and 22 / 36 gear ratio (common as low gear on triples for many years) generate almost the same torque at the rear.

For instance 30 / 50 and pedalling at 90 rpm and at a torque of 10 nm at the cranks, generates at the rear 16.67nm and 54 rpm, and 22 / 36 and pedalling at 90 rpm generates at the rear 16.36nm and 55 rpm.

Thus you are not going to see vastly different torques at the rear that haven't been seen before with triples.

I doubt the torque you can put apply at the crank matches anything close to what World Tour Pros can do.

 

[presta]

I'm slightly concerned that having these modern large rear sprockets (46t+) on a roadbike freehub is creating too much torque for some freehub internal ratchet and pawl designs.

I've changed over to using Hope freehubs, that are based on mtb design and seem a stronger design.

So, lets talk about torque concerning freehubs with large rear sprockets. What do you think?

The torque is determined by the gradient of the hill, the weight of bike & rider, and the size of the wheel. Increasing the sprocket size just reduces the tension on the chain and the torque on the chainset.

Torque = mgrsin(arctanG)

m: mass
g: 9.81 m/s/s
r: wheel radius
G: gradient

 

[presta]

I've changed over to using Hope freehubs

I think Hope hubs are the ones that Chris Juden was criticising for being machined instead of forged, leading to premature failures with fatigue fractures in the flanges at the spoke holes.

 

[GuyBoden]

The torque is determined by the gradient of the hill, the weight of bike & rider, and the size of the wheel. Increasing the sprocket size just reduces the tension on the chain and the torque on the chainset.

Torque = mgrsin(arctanG)

m: mass
g: 9.81 m/s/s
r: wheel radius
G: gradient

The smaller torque at the input chainring side is transmitted as a larger torque at the output rear hub side via the rear sprocket. Obviously, the calculation of this torque depends on the number of teeth in the front chainring and the number of teeth in the rear sprocket.

 

[fossyant]

Like has been said, you are unlikely to provide enough torque to damage a freehub in any gear unless your name is Chris Hoy

 

[GuyBoden]

Like has been said, you are unlikely to provide enough torque to damage a freehub in any gear unless your name is Chris Hoy

That's not my experience, having broken two hubs in the last few years cycling up steep hills (20+% max) with either a 22t + 42t or 24t + 46t (front+Rear).

The ratchet in the hub shears or the pawls break.

Hope mtb hubs on a road bike seem a good choice and have not broken yet.

 

[Jameshow]

That's not my experience, having broken two hubs in the last few years cycling up steep hills (20+% max) with either a 22t + 42t or 24t + 46t (front+Rear).

The ratchet in the hub shears or the pawls break.

Hope mtb hubs on a road bike seem a good choice and have not broken yet.

You had Miche hubs?
What about Shimano hubs?

 

[GuyBoden]

You had Miche hubs?
What about Shimano hubs?

I haven't had any problems with the steel Shimano freehubs, but I use them mostly for flat rides. But, the pawls have gunked up on a few bikes.

Most of the older Shimano freehubs are made from steel, including the ratchet and pawls.

 

[Ajax Bay]

that having these modern large rear sprockets (46t+) on a roadbike freehub is creating too much torque

Why do you think that, Guy? Give us your calculation (assuming a hill of x% gradient and a speed of v mps) with a (say 34t) chainring and a 32t and a 46t sprocket. Anyway who rides a 46t sprocket on a road bike?

The smaller torque at the input chainring side is transmitted as a larger torque at the output rear hub side via the rear sprocket. Obviously, the calculation of this torque depends on the number of teeth in the front chainring and the number of teeth in the rear sprocket.

If it's obvious, it'll be easy to show us.

my experience, having broken two hubs in the last few years cycling up steep hills

Then you say Shimano hubs are OK so which hub (makes) failed you: don't leave us in suspense!

 

[fossyant]

That's not my experience, having broken two hubs in the last few years cycling up steep hills (20+% max) with either a 22t + 42t or 24t + 46t (front+Rear).

The ratchet in the hub shears or the pawls break.

Hope mtb hubs on a road bike seem a good choice and have not broken yet.

I've never broken any freehub, from being a racing snake doing 1 in 4 climbs on 42 x 21, to hauling myself up mountains on an MTB. Possibly crap hubs.

 

[GuyBoden]

I've never broken any freehub, from being a racing snake doing 1 in 4 climbs on 42 x 21, to hauling myself up mountains on an MTB. Possibly crap hubs.

Yes, Miche Syntesi hubs.

Torque is cheap, so fill in the example equation below with your own numbers to calculate approx torque:

 

[fossyant]

I'm going with shoot hubs rather than fretting about amazing power one may have ! I know a few people that are really fast, and one lad who outputs a massive amount of power - hasn't broken a freehub, but bottom brackets, breaking spokes, and rear mechs get bent regular... not saying who...

 

[Ajax Bay]

Torque is cheap,

Very good
The best speed a cyclist rides up a hill of gradient 'x%' will depend on the maximum power they can generate (at any particular moment).
Your 'cheap' hypothesis "concerned that having these modern large rear sprockets (46t+) on a roadbike freehub is creating too much torque":
is that a rider, with a determined peak power (eg in watts), just needs to use a larger sprocket and they will increase the torque delivered to the rear wheel (risking breaking a weak hub) and ride up the hills faster for the the same power?
A pro team needs to sign you up in a consulting role. To advise on not using Miche Syntesi hubs perhaps.

 

[Jameshow]

Very good
The best speed a cyclist rides up a hill of gradient 'x%' will depend on the maximum power they can generate (at any particular moment).
Your 'cheap' hypothesis "concerned that having these modern large rear sprockets (46t+) on a roadbike freehub is creating too much torque":
is that a rider, with a determined peak power (eg in watts), just needs to use a larger sprocket and they will increase the torque delivered to the rear wheel (risking breaking a weak hub) and ride up the hills faster for the the same power?
A pro team needs to sign you up in a consulting role. To advise on not using Miche Syntesi hubs perhaps.

Guy does have a point that torque will break a freehub, so a big rider might well do so. However power is torque x rpm.

So the big guy won't turn over the pedals as fast or as efficiently as the lighter guy who turns the faster.
A diesel engine might produce
250n/m at 3000 rpm

But a petrol

125n/m at 6000rpm
but they are still producing the same HP.

However the diesel will need a bigger drive shaft to account for the torque.