[KaiMana]

Engineers out there: At first blush it would seem that hollow crowns would be significantly weaker, but on the other hand if done right maybe they could be just as strong.

I am specificaly looking at the pike forks where you drop approx. 1/4 lb by going to the team(hollow crown, alum. steerer).

 

[zedro]

last time i checked, most bikes are 'hollow'...

 

[KaiMana]

crowns aren't round though and take forces bending and twisting from more directions than any frame tube.

 

[buildyourown]

crowns aren't round though and take forces bending and twisting from more directions than any frame tube.

The material in the middle does the least amount of good when it comes to stiffness and strength. (for most loads) By making the crown larger and hollow, you can make it lighter and stronger. Cost is the limiting factor.

 

[zedro]

The material in the middle does the least amount of good when it comes to stiffness and strength. (for most loads) By making the crown larger and hollow, you can make it lighter and stronger. Cost is the limiting factor.

yup, and i believe those ultra light Maverick DC forks have hollow crowns which are welded to the uppers. Hollow cranks are another good example and would more ressemble the type of loading crowns have. All the principals are the same, comes down to inertial mass properties.

 

[Sir_Crackien]

most upper end single crown forks are hollow.
psylo,pike,reba,skarabe,shreman(even the slider),minute,black,nixon
don't worry about the crown being hollow. i have ridden hollow crowns for years now and they have never let me down

 

[HTFR]

so you don't think its any weaker?

 

[dropmachine]

I wouldn't worry about the crown, i would worry about the steerer first.

 

[zedro]

so you don't think its any weaker?

its all about the strength to weight ratio, so the specific strength of say a hollow beam is higher than a solid one of equal dimention.

 

[Sir_Crackien]

one thing to remember is surface effects. more load is put on the surface of the object than the hollow part. hollow crowns give you more surface(alot more) and many times are stronger than their solid counterparts(but not always)

and like the other guy said worry about the steerer first

 

[zedro]

one thing to remember is surface effects. more load is put on the surface of the object than the hollow part. hollow crowns give you more surface(alot more) and many times are stronger than their solid counterparts(but not always)

has nothing to do with surface, not sure what school taught you that.

 

[Westy]

Like others have said, the center of a stressed member carries little stress. Generally a solid member is required only in cases of high sheer load, tension/compression. These forces are not much of a factor in crowns. The only major reason to have a solid crown is to reduce manufacturing costs. Once a manufacturer decides on a hollow crown they can decide on a wall thickness that will handle the same abuse as a solid unit.

 

[Westy]

has nothing to do with surface, not sure what school taught you that.

Maybe he is an EE and thinking about high frequency/high voltage electrical applications.

 

[zedro]

Maybe he is an EE and thinking about high frequency/high voltage electrical applications.

i'm thinking its a misconception that i've seen float around some forums, like someone saying hollow BB axles are stronger because they have more surface area

 

[scurban]

I wouldn't worry about the crown, i would worry about the steerer first.

I've seen a ton of 03 crowns crack on Marzocchi DJ forks, which were solid, and very heavy duty. I think it was a design flaw though, because they were really good about warranties with them. They cracked underneath right near two small screw holes, (I'm assumeing that were for fenders) Anyways, I am now riding a nixon, and I must say I was a bit concerned about the hollow crown, but it seems to be holding up just fine.
Beyond the different characteristics of the metals, why worry more about steerers? I have a reallitively long head tube on my frame, so I assume that takes the stess off of the fork, and I can run alloy steer tubes without too much worry, or am I just foolin' myself?

 

[lovebunny]

the dj prob can be solved just by putting screws in the holes i hear

 

[Kornphlake]

the dj prob can be solved just by putting screws in the holes i hear

I highly doubt that, unless you are setting them in with a structural epoxy. The crowns are likely failing because the holes create a stress riser, or an area where stresses are concentrated. Generally smaller radiuses and sharp corners should be avoided as cracks usually start in these areas.

 

[scurban]

I highly doubt that, unless you are setting them in with a structural epoxy. The crowns are likely failing because the holes create a stress riser, or an area where stresses are concentrated. Generally smaller radiuses and sharp corners should be avoided as cracks usually start in these areas.

I'm pretty sure they've fixed the problem, but yeah if screws in the holes would have fixed the problem, they probably would have sent them out as a recall to save warrantying the cracked crowns, it would have been more cost efficient.

 

[zedro]

I highly doubt that, unless you are setting them in with a structural epoxy.

even then, you'd probably need that epoxy and screw to have a similar stiffness as the aluminum with a perfect bond. Even then it might not discount what simply could be a bad design even without the holes.

 

[buildyourown]

I have a reallitively long head tube on my frame, so I assume that takes the stess off of the fork, and I can run alloy steer tubes without too much worry, or am I just foolin' myself?

You're foolin' yourself. The stress is concentrated where the crown meets the steerer. No matter how long your headtube is, the stressed area is still the same.

 

[BikeFan84]

shouldn't be weaker

 

[scurban]

You're foolin' yourself. The stress is concentrated where the crown meets the steerer. No matter how long your headtube is, the stressed area is still the same.

makes sense.

so what should I do, just take my fork off, and inspect it every couple of rides to make sure the steertube is not cracking?

 

[buildyourown]

makes sense.

so what should I do, just take my fork off, and inspect it every couple of rides to make sure the steertube is not cracking?

I wouldn't worry about it, especially if it is a steel steerer.
If the fork is being used for it's designed purpose, it should be fine.

 

[scurban]

actually is alloy.

 

[zedro]

actually is alloy.

steel alloy? aluminum alloy? lotsa different alloys....

 

[scurban]

sorry I ment to say Aluminum