Bicycle Mechanics - 2 Questions wheels and axles

Hey all,

Two quick questions.

I have an older mtn bike that came with a 7 spd freewheel and today I finally broke the axle after using it for about 13 yrs. I had a spare so she's up and running again. Just wondering if I can use a wheel with a QR axle in a frame designed with a nutted axle, and also, can I fit a QR axle to a wheel that originally came with a nutted axle.

take care,
charlie

Yes and yes...

However.

You broke one axle already. A hollow one will not last longer...

QR axle is just a Tube , same thread as a solid one , but if you break a solid axle ,
a hollow QR one will fail sooner. just leave it as is, Or..


Part of a freehub improvement, is it relocated the bearing race to the outboard right end.

You would be advised to buy a new bike rather than convert a slug.

though I toured Europe several times with a 7 speed freewheel in back.
Phil Wood hubs are expensive, but do not break their oversized QR,axles.

Basically, the strength difference between a hollow qr axle and a nutted solid one is not much. The very center of a cylinder lends little to it's stiffness or ultimate strength and that's all that's removed from a qr axle. So, yes and yes as noted but any freewheel hub is going to be weaker than a Shimano freehub since the drive side bearing is much further inboard than on the freehub and the lever arm is longer. However, if you took 13 years to break the first one, a qr replacement using your existing hub should last about as long.

However, if you took 13 years to break the first one, a qr replacement using your existing hub should last about as long.

+1, with a 13 year life expectancy, any discussion of the relative strength of solid vs. QR axles is kind of moot.

One note on substituting, Rear axles are generally 3/8" (9.5mm) or 10mm in diameter, with QR versions available for both, and dropouts are almost always 10mm, so subbing is easy. But many solid front axles are only 5/16", and forks made for them the same, so even if you could find the QR axles and cones for a changeover, you'll also need to file the slots in the fork wider. This isn't a serious problem, but you have to be careful to preserve the axle alignment when you do so.

With a qr axle both ends of the axle must be within the thickness of the dropouts. The quick release must tighten against the dropouts, not against the axle. If needed the axle can be cut shorter.

QR axle is just a Tube , same thread as a solid one , but if you break a solid axle ,
a hollow QR one will fail sooner. just leave it as is, Or..


Part of a freehub improvement, is it relocated the bearing race to the outboard right end.

You would be advised to buy a new bike rather than convert a slug.

though I toured Europe several times with a 7 speed freewheel in back.
Phil Wood hubs are expensive, but do not break their oversized QR,axles.

I don't appreciate you calling my bike a slug, this faithful stead has over 50,000 miles on it and over the years I done a few upgrades. As for buying a new bike, what would serve me better? Replacing a wheel with a freehub body and cassette would be far cheaper than a new bike. Read the rest of the replies to my questions and notice how useful they are.

With a qr axle both ends of the axle must be within the thickness of the dropouts. The quick release must tighten against the dropouts, not against the axle. If needed the axle can be cut shorter.

Thanks man, I'm aware of this fact.

+1, with a 13 year life expectancy, any discussion of the relative strength of solid vs. QR axles is kind of moot.

One note on substituting, Rear axles are generally 3/8" (9.5mm) or 10mm in diameter, with QR versions available for both, and dropouts are almost always 10mm, so subbing is easy. But many solid front axles are only 5/16", and forks made for them the same, so even if you could find the QR axles and cones for a changeover, you'll also need to file the slots in the fork wider. This isn't a serious problem, but you have to be careful to preserve the axle alignment when you do so.

Thanks, great advice and just what I was hoping for and expecting from this form

Basically, the strength difference between a hollow qr axle and a nutted solid one is not much. The very center of a cylinder lends little to it's stiffness or ultimate strength and that's all that's removed from a qr axle. So, yes and yes as noted but any freewheel hub is going to be weaker than a Shimano freehub since the drive side bearing is much further inboard than on the freehub and the lever arm is longer. However, if you took 13 years to break the first one, a qr replacement using your existing hub should last about as long.

Thanks, I thought as much, nice to have it confirmed by someone who knows.

Basically, the strength difference between a hollow qr axle and a nutted solid one is not much. The very center of a cylinder lends little to it's stiffness or ultimate strength and that's all that's removed from a qr axle...I think there's a chance the nuts brace the solid axle from bending better than the qr does.

Not to mention, part of the load on an axle is tensile because in order for the axle to bend, it also has to lengthen due to the cone pivoting on the ball bearing that is taking the load.

I mean the bearing taking the load is the fulcrum around which the axle bends.

The metal in the middle of a solid axle takes plenty of the load of the axle trying to elongate so as to bend about the ball which is taking the load, which in turn reduces the stresses on the outer surface, because stresses are cumulative.

I think there's a chance the nuts brace the solid axle from bending better than the qr does.

Not to mention, part of the load on an axle is tensile because in order for the axle to bend, it also has to lengthen due to the cone pivoting on the ball bearing that is taking the load.

I mean the bearing taking the load is the fulcrum around which the axle bends.

The metal in the middle of a solid axle takes plenty of the load of the axle trying to elongate so as to bend about the ball which is taking the load, which in turn reduces the stresses on the outer surface, because stresses are cumulative.
I eapect the qr clamp faces brace the axle against the locknuts about as much as the nuts do and an internal cam qr may even do it better.

A bending axle experiences both tensile (the outside of the curve) and compressive (the inside of the curve) stress.

The small hole in a hollow axle does very little to reduce its to bending resistance since the stiffness of a tube is proportional to the 4th power of it's diameters so the OD is vastly more of a contributer than the ID. S= K(R^4-r^4) where R=OD and r=ID and since r is small, it's contribution is also small. This is why a larger diameter tube of a lower modulus material like aluminum can have equal or greater stiffness than a smaller diameter higher modulus steel tube.

All of that said, except for very large impacts, freewheel axles fail from fatigue stress, not from overloads, and a nutted axle is no more immune than a qr axle.

With the Internet, you'll get responses you like and some you won't. Sounds like you'll be in good shape whether you stick with freewheels or switch to freehubs. If you want to relace the rim to a 7-speed freehub with the same flange height or pick up a used 7-speed wheel, you should be able to do it without spending much. :thumb:

A bending axle experiences both tensile (the outside of the curve) and compressive (the inside of the curve) stress. I think you're wrong. The axle experiences a small tensile stress on the side facing the load due to the camming effect of the cones, and a large tensile stress on the side opposite the load.

It is essentially being stretched over the side of the hub facing the load by the cones pivoting about the ball bearings.

Do not show me a picture from a statics text. You people do not know how to pick the right kind of picture. The arrows are wrong and the ends are wrong when you guys pick the picture.

http://kcsbikes.com/Fpics/29_square_wheels.jpg.FP

I think you're wrong. The axle experiences a small tensile stress on the side facing the load due to the camming effect of the cones, and a large tensile stress on the side opposite the load.

It is essentially being stretched over the side of the hub facing the load by the cones pivoting about the ball bearings.

Do not show me a picture from a statics text. You people do not know how to pick the right kind of picture. The arrows are wrong and the ends are wrong when you guys pick the picture.
Pictures, what pictures? :)

OK, I accept your analysis of the bending load distribution but still maintain that in realistic use, a hollow qr axle gives up nearly nothing to a nutted axle.

Pictures, what pictures? :)

OK, I accept your analysis of the bending load distribution but still maintain that in realistic use, a hollow qr axle gives up nearly nothing to a nutted axle.

I love these academic debates. You're both right and both wrong at the same time. The location of the neutral axis depends on the type of bearing (angular, vs. radial) amount of bearing play, and the extent that the cone/locknut are braced against the dropouts face.

In any case axles don't break from single overloads, but through metal fatigue from repeated flexing. They always break at stress riser caused by the root of the first thread outside of the cone. The best way to prevent failure is to eliminate the threads, as many designs do.

FWIW- most experienced shop mechanics will tell you that they see roughly the same number of broken solid and QR axles, but that doesn't mean anything because the QR axles may tend to be of better quality, but also may see more use.

I love these academic debates. You're both right and both wrong at the same time. The location of the neutral axis depends on the type of bearing (angular, vs. radial) amount of bearing play, and the extent that the cone/locknut are braced against the dropouts face.

In any case axles don't break from single overloads, but through metal fatigue from repeated flexing. They always break at stress riser caused by the root of the first thread outside of the cone. The best way to prevent failure is to eliminate the threads, as many designs do.Overload or repeated stress, the intensity of the stress has a lot to do with fatigue life. If you keep the intensity below a certain threshold, steel would have an infinite fatigue life, and increasing intensity above the threshold has a linear effect on fatigue life as I recall.

Why worry about other types of bearings that don't go in a 7 speed freewheel hub? I don't think it's a sealed Phil Wood.

I think the neutral axis is between the axle and the side of the hub facing the load, regardless of the type of bearing, however. Though, hypothetically, a press-in radial bearing might reduce the tensile load by eliminating camming the cones apart.

Overload or repeated stress, the intensity of the stress has a lot to do with fatigue life. If you keep the intensity below a certain threshold, steel would have an infinite fatigue life, and increasing intensity above the threshold has a linear effect on fatigue life as I recall.

Why worry about other types of bearings that don't go in a 7 speed freewheel hub? I don't think it's a sealed Phil Wood.

I think the neutral axis is between the axle and the side of the hub facing the load, regardless of the type of bearing, however. Though, hypothetically, a press-in radial bearing might reduce the tensile load by eliminating camming the cones apart.

You're much more highly invested in this debate than I am. I was only trying to point out that there were more variables than accounted for. As pointed out the axle life was very reasonable, and as long as it remains so there's no point in trying to fix it. If/when someone has a problem where the actual service life is too short, I'll post some practical solutions.