Coolpick87

Hey.

I'm looking for the forque rating for a single speed freewheel like https://https://www.amazon.com/Dicta-1.../dp/B001F2URGY

I asking about the strenght of freewheels not how much torque to apply when tighten.

Thanks

Kimmo 

NFI how to find out, but it's almost certainly more than you need.

Unless you plan to put V8 power through one or something...

I reckon it's safe to say an aluminium hub's threads would strip first.

surreal

pssssssssssssst-- here's a secret: thread the freewheel on, and finger-tighten it. Then, go for a ride. Congrats! You've just applied the correct amount of torque.

-rob

Coolpick87

Well, I'm asking because I'm looking tor buy a one way roller bearing for a different project.

I was wondering the strength so I could translate it over to the roller bearing and pick out the correct size.

Thanks

Kimmo 

Hmm, you could mount an inline scale between some chain wrapped around your chainring and cog, see how much force the chain exerts on the cog, and do some maths...

Bezalel

Why kind of numbers are you dealing with? Or what is the project?

Doohickie

Okay. How much do you weigh? 200 lb.? Maybe a heavy rider is twice that? Apply 400 lb. through your drivetrain, applying the various mechanical advantages (crank arm > chain ring > cog) and that should give you a pretty good idea. I have a 46/18, not sure about the crank length, but let's say it's a 170 mm.

So, force is applied at 170 mm = 6.7 inches

Torque applied about the crank is 6.7 x 400 = 2,680 in-lb (= 223 ft-lb)

With an 46/18 gear ration, the torque at the rear axle is 18/46 x 223 = 87.4 ft-lb.

So the torque applied at the rear axle by a 400 lb. rider putting all his weight on one crank through a 46/18 gear train is 87.4 ft-lb. That gives you a factor of 2 over a 200 lb. rider. If you're looking for a rating for the torque on the freewheel, it's probably somewhere around there, like maybe 100 ft-lb. I suspect the actual rating is a little higher than that.

FBinNY 

Given that the chains that run on them are typically rated to 1,100kg or so, I'd work out what torque that would produce based on the sprocket radius, (roughly 1.5" on a 15t). The freewheel should be built to withstand the chain's max load, so that would be a starting place. Odds are that they're even stronger than that.

tatfiend 

IMO it will vary sepending on make of freewheel and the quality of materials used. The White Industries freewheels, particularly the special trials version, are probably the strongest as they use 3 or more ratchet arms internally.

The calculation provided by Doohickie is probably the best estimate you will find.

FBinNY 

Actually this is a very conservative estimate, which assumes a large chainring. If the chainring were halved the torque would double. Likewise if the rear sprocket were larger. Since builders of freewheels don't know what sprockets will be used they have to allow for the most unfavorable situation, the limiting factor being chain strength.

I'd estimate that a range of 250 - 300 ft#s of torque would still be a conservative estimate ot their capacity.

Consider that the mechanism is the same as used on freewheels which use sprockets of 30t or more, driven by grannies. If you use Doohickie's analysis assuming a 24/30 combination you'd see that even my estimate might be conservative.

Obviously quality of construction is a factor, but the basic design is at the top of the scale for torque capacity in the category of over-running clutches.

Doohickie

Good point. That's part of why I doubled the size of the rider to begin with.

ElliotN

A decade later, this thread comes up when I search on the same question!

Any progress?

I am also working on a custom project -- a three-person pedal-car with 48-inch tall tires (penny-farthing wheels). The vehicle belongs to a friend and it used to have bicycle wheels, but I lucked into two of the penny-farthing wheels and want to use them to give the vehicle a steam-punky style.

So, I need to install some form of low-friction freewheeling mechanisms in the hubs of the penny-farthing wheels (which are replicas by Rideable Bicycle Replicas in Alameda, Northern California).
And I am looking at one-way bearings such as this:

https://www.vxb.com/CSK25PP-One-way-p/kit10971.htm

This one is good for 68 N.m, which appears to equal 50 pound/feet.

I have build a few large pedal-vehicles for Kinetic Sculpture Racing, but I always incorporated BMX freewheels further upstream in the drivetrain. Trouble with that, is the friction of chains and bearings downstream of the freewheel when the vehicle is coasting.

Yes, I can attach BMX freewheels to the penny-farthing hubs. But this is all about doing something "cool" and "neat". So, I am thinking about these industrial one-way bearings.

In the snapshot below, the new wheels are only loosely mocked up in position.

Thoughts? Facts? Good-natured ridicule?
Thanks!

70sSanO

I would think freewheels that are used on mid-drive ebikes should give you enough info. You can figure out the motor torque and go from there.

John

Kimmo 

At a guess, 68Nm seems a bit wimpy... bike drivetrains are unusually low rpm, high torque. But I guess since it's a trike, we're talking 136Nm of capacity? Is there a differential?

63rickert

Not sure if this will be useful information for the current project but...

Bicycle freewheels are strong. Real strong. Over the years I have known freakishly strong riders who do pop chains. Who do strip threads off the hub shell. Who twist Campagnolo crankarms. Who shear off pedal spindles. Freewheels are not a problem for those guys. Sure the little pawl springs fracture and they don’t work when lubrication fails. They do hold up to extreme load. Do not expect problems.

rickpaulos

sounds bizarre but I had a trail-a-bike in for repair (with single cog freewheel) where the kid stripped the freewheel threads off the hub.

I'd be looking for a decent hub for the project. Avoid those stamped sheet metal bso hubs. I've seen scores of failed hubs. Freewheel issues are almost always due to lack of any maintenance. Pawls getting stuck 'open' in -30F weather or rusty from being left out doors in the rain and snow.

and don't get a freewheel that has no remover slots. yeap, they make em like that.

For that creation, I don't think high speed is going to be an issue. You may need a 22t freewheel.

Andrew R Stewart 

Roller clutches have been used by the bike business for a long time although any one manufacturer's data might not be public I do remember that some problems with alloy hub shells withstanding the outward force the rollers can exert. Something about hub shells cracking about the clutch's circumference. IIRR one company solved this with a wrapping band of carbon around the clutch portion of the hub shell.

I'll add that roller clutches can have a somewhat different engagement "feel" compared to a ratchet design. Less "hard/solid" with initial engagement. Although for a while the police liked the silent coasting Andy

ClydeClydeson

I would use Doohickie 's strategy for estimating, but I would change the equipment to work out how much abuse would be possible under worst conditions.

I will use a 200kg (440lb, 1960N)) rider putting all their weight on a 185mm crankarm
Lets use a 20t small cog (smallest commonly available chainring)
and the largest available SS freewheel sprocket: 28 teeth was the largest I found in a 2 second search

T = 1960N X 0.185m X 28t/20t = 507Nm
or
T=440lbs X 185mm/305mm/ft X 28t/20t = 374 ft-lbs

ClydeClydeson

PS

THat's a big number - the 2.5L engine in my car only puts out 163 ft-lbs, but that's at some 1000s of RPMs.

I weigh about 110 kg (242lbs, 1078 N) and have 180mm cranks, and the low gear on my mtb is 22-32:

T=1078N X 0.18m x 32t/22t = 282 Nm, or about 207ft-lbs. So my Deore freehub body regularly sees a torque of 207 ft-lbs (at ~0 RPM)

cbrstar

As a BMX'er....

I could be a bit wrong on this. But with BMX in the first Olympics I believe Jason Richardson was peaking at 2,328 watts But I don't know how to work out the torque because I don't know the gear ratio. With the older style BMX freewheels the chain always snaps first. I've taken part vintage Suntour bmx and road bike freewheels and found that the pawls etc were quite similar. In 3rd world countries many have bicycle powered carts and haul huge amounts of weight.

But modern BMX 9t cassettes seem to brake often. The pawls chip or wear out, and the springs seem to break. They tried to go with a 8t and the torque was sheering / breaking the teeth off them. So I can't help but think a 18t is going to be a little stronger then a 16t.

ElliotN

Wonderful! I am mighty impressed with all these well-thought-out responses.

Yes, bicycle freewheels is probably the best way for me to go. And yes, they are generally stronger than the chain.

No differential. Instead, two riders will power one of the drive-wheels, and one rider (the strongest of the three, generally) will power the other drive-wheel. No connection between the two drive-trains. This way, no single failure will completely disable the vehicle. Also, individual control of the drive-wheels can be used to help the vehicle make tight turns.

The hub of the penny-farthing wheel is 6 inches wide.
So, I can stack a handful one-way bearings thru that hub. And thanks to the nature of the design, they would all share the load. That is, the roller-sprag-clutch design engages immediately.
Ratcheting bicycle freewheels, on the other hand, have free-play, and they would be synchronized only occasionally by sheer fluke, so only one of them would carry the load at any one time. And I could not easily install more than two per wheel. Still, this may be perfectly adequate.

Total drive ratio is not an issue, since there will be a jackshaft, where I can juggle any number of teeth I want. In fact, there will probably be a freewheel (a spin-on freewheel cluster from a mountain bike) on each jackshaft. What I am trying to avoid is having the jackshafts spinning whenever the road-wheels are moving.

Let me see if I can make a drawing, and maybe take a photo or two.
But yes, you are close to convincing me to forget about the industrial roller clutches.