Reinforcing carbon fiber steerer tube

Waspinator · Dec 28, 2013

Please, don't bother responding to this question with statements like "why bother?" or "what's the point?". I am asking this more as an academic question more than anything else.

If one wanted to reinforce a carbon-fiber steerer tube (along the entire length of the tube), what approaches could be taken to do this that wouldn't add too much weight?

For example, I was thinking that mixing epoxy with small styrofoam pellets, and filling the steerer tube with it (to create somewhat of a "pneumatized" structure like the long bones found in birds, which are extremely strong) might be one option. Any other ideas? A thin-walled tube of smaller diameter glued into the steerer tube could be another approach, perhaps?

Also, I'm wondering: are steerer tubes on forks actually carbon-fiber, or something else? They don't seem to have the glossy epoxy finish and carbon-fiber cross-hatched weaved cloth that you find in other carbon fiber parts. Would epoxy even bond to it?

pulser955 · Dec 28, 2013

What do you want to accomplish? There are a few plugs that will reinforce the tube at the stem to prevent crushing. I don't know that you really need any reinforcement any place other than that.

My Own Private Idaho · Dec 28, 2013

You could use an aluminum sleeve, bonded inside the carbon post.

tihsepa · Dec 28, 2013

What are you trying to accomplish?
Undamaged steer tubes are not just breaking off all the time.

Waspinator · Dec 28, 2013

pulser955 said:
What do you want to accomplish? There are a few plugs that will reinforce the tube at the stem to prevent crushing. I don't know that you really need any reinforcement any place other than that.

View attachment 290236

To my knowledge, no one has ever snapped off an aluminum steerer tube while riding a road bike. CF steerer tubes are a different story, if I'm not mistaken. And let's face it, a steerer tube is an absolutely lousy place for a bike to fail. There are a lot of us - especially bigger cyclists - who are quite frankly squeamish about CF steerer tubes.

Steerer tubes are take a lot of forces in a wide variety of directions while essentially keeping the front half and the back half of a bicycle together as one functioning unit. They are the cycling equivalent of the Jesus pin on a helicopter (which keeps the main rotor attached to the main shaft). As such, they ought to be outright bomb-proof. I personally think that CF steerer tubes epitomize irresponsible design, but unfortunately, nowadays if you want a top-end bike you're going to get a CF steerer. There ought to be a way to add strength to them without increasing the weight too much.

looigi · Dec 28, 2013

Cervelo uses an epoxy in aluminum plug instead of an expanding plug. This reinforces the steerer near the top headset bearing and stem. If the diameter fits your fork, this would be a good way to go. If not, fabricating something similar would good. Further down in the steerer? If it had to be done, you could lay in some pre-preg unidirection CF, a balloon, and cure it...

Waspinator · Dec 28, 2013

tihsepa said:
What are you trying to accomplish?
Undamaged steer tubes are not just breaking off all the time.

Cyclists don't fall off their bikes all the time either, but they still wear helmets. We're talking about taking precautions. Steerer tube breakage is catastrophic.

tihsepa · Dec 28, 2013

Waspinator said:
To my knowledge, no one has ever snapped off an aluminum steerer tube while riding a road bike. CF steerer tubes are a different story, if I'm not mistaken. And let's face it, a steerer tube is an absolutely lousy place for a bike to fail. There are a lot of us - especially bigger cyclists - who are quite frankly squeamish about CF steerer tubes.

Steerer tubes are take a lot of forces in a wide variety of directions while essentially keeping the front half and the back half of a bicycle together as one functioning unit. They are the cycling equivalent of the Jesus pin on a helicopter (which keeps the main rotor attached to the main shaft). As such, they ought to be outright bomb-proof. I personally think that CF steerer tubes epitomize irresponsible design, but unfortunately, nowadays if you want a top-end bike you're going to get a CF steerer. There ought to be a way to add strength to them without increasing the weight too much.

Makes sense. To be honest I am more worried about the aluminum steer tube bonded to the carbon fork than a full carbon fork.

pulser955 · Dec 28, 2013

Waspinator said:
To my knowledge, no one has ever snapped off an aluminum steerer tube while riding a road bike. CF steerer tubes are a different story, if I'm not mistaken. And let's face it, a steerer tube is an absolutely lousy place for a bike to fail. There are a lot of us - especially bigger cyclists - who are quite frankly squeamish about CF steerer tubes.

Steerer tubes are take a lot of forces in a wide variety of directions while essentially keeping the front half and the back half of a bicycle together as one functioning unit. They are the cycling equivalent of the Jesus pin on a helicopter (which keeps the main rotor attached to the main shaft). As such, they ought to be outright bomb-proof. I personally think that CF steerer tubes epitomize irresponsible design, but unfortunately, nowadays if you want a top-end bike you're going to get a CF steerer. There ought to be a way to add strength to them without increasing the weight too much.

They make suspension forks with carbon steerer tubes. To my knowledge they don't fail very often and they are subjected to much harsher forces than any thing you're going to do on the road. Carbon is much stronger than aluminum. The problem is when people crush the tube with the stem. Other than that I don't really know of any wide scale problem with carbon tubes.

tihsepa · Dec 28, 2013

Get a steel bike.
I tour on a Surly LHT. The fork will hold up fine.

Waspinator · Dec 28, 2013

tihsepa said:
Makes sense. To be honest I am more worried about the aluminum steer tube bonded to the carbon fork than a full carbon fork.

Good point. That certainly does raise questions too.

However, the carbon fiber around the stem is particularly vulnerable. It's being squeezed by stem, pulled side to side by the rider, all while supporting some of the rider's weight (which can increase dramatically when hitting bumps). And its doing all of these things right above the upper headset bearing.

PlatyPius · Dec 28, 2013

Waspinator said:
Please, don't bother responding to this question with statements like "why bother?" or "what's the point?". I am asking this more as an academic question more than anything else.

If one wanted to reinforce a carbon-fiber steerer tube (along the entire length of the tube), what approaches could be taken to do this that wouldn't add too much weight?

For example, I was thinking that mixing epoxy with small styrofoam pellets, and filling the steerer tube with it (to create somewhat of a "pneumatized" structure like the long bones found in birds, which are extremely strong) might be one option. Any other ideas? A thin-walled tube of smaller diameter glued into the steerer tube could be another approach, perhaps?

Also, I'm wondering: are steerer tubes on forks actually carbon-fiber, or something else? They don't seem to have the glossy epoxy finish and carbon-fiber cross-hatched weaved cloth that you find in other carbon fiber parts. Would epoxy even bond to it?

why bother?
what's the point?

BlueMasi1 · Dec 28, 2013

Wood dowels.

Guod · Dec 28, 2013

I think someone with industry knowledge needs to respond to this.

Personally, I worry more about whether or not I put sufficient tension on my quick releases on my wheels. I've hit potholes hard enough to cause my bars to slip in the stem clamp and nothing happened to the steerer. Note to alarmists: my bars and stem are both alloy, torqued to spec. I think it's needless worry to be paranoid about the steerer, just like my paranoia about quick releases.

velodog · Dec 28, 2013

Waspinator said:
To my knowledge, no one has ever snapped off an aluminum steerer tube while riding a road bike.

When Hincapie's steerer broke in the 2006 Paris Roubaix, taking him out of the race with a separated shoulder, it was an aluminum steerer bonded to a carbon fork. The break was just below the stem clamp, which means the steerer broke not the aluminum to carbon bond.

Stuff happens.

velodog · Dec 28, 2013

BlueMasi1 said:
Wood dowels.

When I was a kid a friend had a 165cc motorcycle and he wanted a chopper, so he stole a broom from his mother and cut two six inch sections out of the handle and forced them into the forks to extend them. He took his "chopper" with the six inch extended forks out for its maiden voyage and didn't even get around the block before the modification failed catastrophically.

He busted up his face pretty good, and all any of us did to help was laugh our asses off. It was one of those things that you never forget.

cxwrench · Dec 29, 2013

My Own Private Idaho said:
You could use an aluminum sleeve, bonded inside the carbon post.

^ This would work. As someone else posted, it's how Cervelo does it. ^

redondoaveb · Dec 29, 2013

cxwrench said:
^ This would work. As someone else posted, it's how Cervelo does it. ^

Alpha Q does it with their forks also.

brianmcg · Dec 29, 2013

You could buy a Surly Pacer and have no worries at all.

Insight Homewood · Dec 29, 2013

I suggest you ask the manufacturer of your carbon fiber fork/steerer tube what strength it has vs an aluminum one. The very best springs made are now carbon fiber because they can be designed with a fatigue life far beyond what normal mortals would be able to apply to them. As far as I know, the main bicycle manufactures are not on the carbon fiber bandwagon as a fad; they are afraid of product safety recalls that could sink a company. For that reason alone, carbon bikes are over-designed in strength and fatigue strength to make them as bombproof as possible. Calfee Design, in their dragon fly bike, mix carbon fiber with boron fiber to make the tubes much tougher for the weight and damage-resistant.
:aureola:

Reinforcing carbon fiber steerer tube

Waspinator

pulser955

My Own Private Idaho

tihsepa

Waspinator

looigi

Waspinator

tihsepa

pulser955

tihsepa

Waspinator

PlatyPius

BlueMasi1

Guod

velodog

velodog

cxwrench

redondoaveb

brianmcg

Insight Homewood

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