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Rage Against Hollow Bolts

Written by Saris Mercanti
20 Comments
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Hollow bolts have undergone widespread adoption in BMX components in recent years in an effort to win the weight game. Unfortunately, some riders have experienced these bolts catastrophically failing, as documented humorously in this video. “Bolt tunning” in a high risk discipline like street or park BMX is just stupid. While large hollow bolts may be acceptable on certain components such as cranks (guilty), using small ones for minimal weight savings on stems is absolutely risky.

Where do you stand on hollow bolts? Are you guilty of swapping out your steel bolts for titanium, aluminum, or carbon bling?

Special thanks to reader Ethan for the link.
Saris Mercanti
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Mindless
Mindless
12 years ago

The problem is cheap crap from China. That’s what fails. Well made hollow bolts are plenty strong.

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RUSTYDOGG
RUSTYDOGG
12 years ago

I suspect there is a different torque spec for hollow bolts. I doubt these brainiacs own a torque wrench or the data.
Why would one want to save a few grams of weight for bikes like these that take so much abuse. I can understand it for a high end race bike, but not here.

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PhdME
PhdME
12 years ago

I am with rustydogg, why would you want to save weight with these bikes?! But, I guess that is beside the point. All bolts have a torque spec, and if you don’t follow that and go past the yield point of the bolt then the bolt is good for nothing. My guess would be that the hollow bolts have a little bit lower yield point, but it depends on how it’s made and who made it. Almost all bmxers, tighten the crap out of all their bolts, because either they don’t want to keep re-tighten them or because they don’t know ow to do it properly.
Lesson of the day……get a torque wrench!

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I_am_an_Engineer
I_am_an_Engineer
12 years ago

It could be too much torque contributing. It’s surprisingly easy to bring small fasteners to yield (and hence closer to ultimate failure). However, in general, hollowing out small bolts is just an awful idea unless you (a) have a very good understanding of the load cases you will see (which you don’t in this kind of cycling) and (b) have analysts and engineers who understand load distribution and how to properly analyze to ensure safety.

In aerospace (where weight is always an issue) you would never hollow out a bolt. Fasteners are usually already the weakest link in the chain. You optimize the parts (stem, bars, etc), not the bolts, and you save a lot more weight.

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Mr. P
Mr. P
12 years ago

@RUSTYDOGG: “why would you want to save weight with these bikes?!”

Such a ridiculous statement. If you bunnyhop/manual/jump etc. you would know why you would want to save weight. I agree with your strength to weight point tho.

That said, hollow bolts on a stem? That is crazy. For what 5g in savings?

P

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PsiSquared
PsiSquared
12 years ago

Uhm, hollowing out a bolt is a great way to greatly increase the stress on a bolt, which moves things much further along toward yielding. If you don’t understand how you’re changing the stress on the bolt and thus what torque is required and what max torque is….well………then you deserve to get smacked in the forehead with the Dick of Reality.

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CW
CW
12 years ago

Good thing he was wearing a helmet…
Things could have easily turned out different and he would be rolling with the two wheels at his sides and have to wear a helmet for the rest of his life at all times.

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Brad
Brad
12 years ago

hollow bolts in the stem might save 2 grams. come on people. there are better options. if you are going to do something like this(which is stupid, even bigger hollow bolts are only going to save you 10-15 grams, use ti) get some grade 5 or 8 bolts and drill those.

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shkoogy
shkoogy
12 years ago

Maybe if the fool didn’t try nose diving into the flat ground!

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Rob
Rob
12 years ago

Lot of negative comments here, especially about the riders.

Any company that manufactures stuff for BMX should ensure that their products can be used by someone who does not own a torque wrench, which essentially means over engineering the component, bad for weight good for safety. The transient forces that BMX components can experience are massive, much much greater than any road bike or mountain bike.

So I agree that hollow bolts on something like a stem are kind of dumb, thats the fault of the company.

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royalewithcheese
royalewithcheese
12 years ago

I have hollow stem bolts from The Shadow Conspiracy in my BMX bike, theres plenty of steel in an 8mm bmx stem bolt to drill the middle out of and save a pretty decent amount of weight. My road bike has KCNC cranks which use massive 7075 bolts and I haven’t run into any issues with them in a year of riding. All of my water bottle cages are held on with aluminum bolts, and I’d be perfectly happy to attach my bottle cages with plastic bolts if they were free.
That being said there are much better places to save weight, and none of my bikes are all that light.

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Rustydogg
Rustydogg
12 years ago

@Mr.P
If you are going to quote someone be sure to use their exact words. Particularly if you are going to condemn their statement.
A hollowed out fastener is a dumb place to loose weight for such an abusive application. All those kids need to do is take their bag of pot out of their pocket and the weight savings is made.

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DaleC
DaleC
12 years ago

DIY hollow bolts are just dumb. Engineers do things for good reasons.

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snaxbmx
snaxbmx
12 years ago

I ride bmx, most of my friends ride bmx. hollow bolts are what come stock in most stems and many other parts. If this silly jamoke learned how to not nosedive into the ground his hollow bolts would probably be just fine. I ride hollow bolts, have for years, if I were in this situation I would blame my riding style and unfortunate fall for my parts breaking. not everything that breaks is the products’ fault… 90% of the time it has been abused by the user at some point whether it breaks in a normal use situation or not… you landed shitty, deal with it, bars probably would have bent if the stem bolts didnt break… Ignorance can definitely be bliss..

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snaxbmx
snaxbmx
12 years ago

@rustydogg REally? a pot reference? dont talk shit to anyone even if they are talking shit if you are going to base your opinions off stereotypes from the ’90’s..

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Rob
Rob
12 years ago

@ Rustydogg

Dont be judgemental. I happen to know a bunch of BMX riders who dont drink, smoke or do drugs.

And if these bolts are DIY that really is dumb, who knows what kind of pre-stresses you are putting into these things!

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DeeEight
DeeEight
12 years ago

The key to USING hollow bolts or any lightweight alternative bolt safely is having a basic idea of how the components are loaded and whether the bolt is taking the load in tension, compression, or if its a shearing load. Crank bolts are fine to save weight, because all the bolt does is to keep the crankarm from walking its way off the spindle under load, thus its in tension/compression… something a bolt handles well in any situation if the crankarm was installed properly in the first place (ie, don’t use the aluminium 8mm bolt to install the square taper crank arm…. use a steel one and then replace it with the Al one after its on). Brake caliper bolts are okay to do in an lightweight alternative with post mounts because again the loads are all in tension/compression… but not with I.S. Flange mounts as the brake loads are all trying to shear the bolt which is where it’ll be at its weakest.

As to stem bar clamp bolts… whether mtb, road, or bmx… titanium bolts are okay for this task, or hollow STEEL bolts would be ok too… but if you watch the video… those don’t look like steel stem bolts that broke. They look very much like hollow aluminium bolts. And that’s just all kinds of stupid there. Take the weakest material, and then hollow it out further. You can tell the material under the colour surface treatment if you watch where they examine the bolts in their hands… sheared off Al bolts are a white-ish center colour, steel is silvery, titanium is a sorta satin-sand colour.

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RUSTYDOGG
RUSTYDOGG
12 years ago

. You’re right that wasnt nice. I take it back 🙂 but you got my point.

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MMyers
MMyers
12 years ago

Can I be the helmet Nazi?

How dangerous does an activity need to be before one wears one?

What’s going on in that video would be way above my threshold.

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Bayard
Bayard
12 years ago

If you are willing to deal with them failing, what’s the beef?

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pissface
pissface
11 years ago

Tbh though if you actually notice his landing, he landed wrong, on his front wheel, and was gonna dive anyway. The stem wouldn’t have taken that much abuse in the first place had he landed properly.

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