Bicycle Mechanics - Frames with injected foam cores

I may be missing something obvious but I have always wondered why bike frames don't have foam (or some similar light material) injected into them.

I would imagine it would help with a number of issues, especialy with the new thin wall frames (both Al & steel) such as the following:

dampen vibration
increased structural integrity
help absorb light impacts so frames dent or ding less

I understand Bianchi now lines the inside of their "super thin wall" racing frames w/ some sort of foam.

Has anyone seen this or can anyone explain what I'm missing as to why this would not work? It would only add 2-4 oz to the frame.

I have half a mind (but even less money) to go buy a used cannondale frame and spray in one of those self expanding foams just to see what would happen.

The down tube and lower half of the seat tube would be accesible in most frames. The head tube obviously would not work and the top tube may be inaccesible as well.

Thanks in advance for any info you might have.

Very interesting. Sounds like it couldn't hurt for only a couple of OZs. The thing I'd worry about is trapping moisture in my steel frames. Although you could do Frame-Saver then the foam.
Report back what you find out, especially how much added weight it is.

I may be missing something obvious but I have always wondered why bike frames don't have foam (or some similar light material) injected into them.

I would imagine it would help with a number of issues, especialy with the new thin wall frames (both Al & steel) such as the following:

dampen vibration
increased structural integrity
help absorb light impacts so frames dent or ding less

I understand Bianchi now lines the inside of their "super thin wall" racing frames w/ some sort of foam.

Has anyone seen this or can anyone explain what I'm missing as to why this would not work? It would only add 2-4 oz to the frame.

I have half a mind (but even less money) to go buy a used cannondale frame and spray in one of those self expanding foams just to see what would happen.

The down tube and lower half of the seat tube would be accesible in most frames. The head tube obviously would not work and the top tube may be inaccesible as well.

Thanks in advance for any info you might have.

Interesting question. Make sure you use the type of foam that only expands minimally, or you'll blow out the tubes! (or make a mess, at a minimum)

Great idea! In fact, it's so great someone is already using it. Check out the Sampson Sports website...it's called SAS (Sampson attenuation system).

Get some crack sealer expandable foam from home depot. That stuff'll fill up and cure to a hard foam.

I may be missing something obvious but I have always wondered why bike frames don't have foam (or some similar light material) injected into them.
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What about if you ride into a lake, then it would float! ;)

What about if you ride into a lake, then it would float! ;)

No, you would drown as the clipless cleats rapidly rust and seize and the bike drags you to a watery grave with it, as things should be. When your bike goes down, you go down with it.

Didn't the Kona cindercone have carbon material inside the tubes? I may be wrong.

Working for a "foam manufacturer" I can say that it is possible to inject certain types of expandable foam (expandable polystyrene as an example) into the frame in liguid form, but you could not control the quality of application for all parts of the frame. Newer foam products are coming on the market soon that will have multi-impact, long-life properties that will, avoid the pun, fill the void for this application. Here is one use of a very lightweight foam. http://www.gtmanga.com/listoftoys/Mogu/mogu.html

dampen vibration
increased structural integrity
help absorb light impacts so frames dent or ding less


dampen vibration - foam would do that. So will cabon fiber or titaium with no added weight.

increase structural integrity - Actually, a hollow tube is much more resistant to bending than a solid tube. Bikes are not bending in half so adding material is not needed.

help absorb light impacts so frames dent or ding less - if you hit it hard enough to dent the metal. Lightweight foam is not going to help. It would have to be very dense, ie heavy, foam to provide any protection.

It could also trap moisture in any voids.

No, you would drown as the clipless cleats rapidly rust and seize
Must be talking about Shimano spuds

Actually, a hollow tube is much more resistant to bending than a solid tube.

Same principle is why injecting air into concrete causes it to be lighter, but stronger. A tube with some type of honeycomb internal structure might possible be stronger, and also more rigid. While I am a newbie, I think I would rather have a frame that had some flex to it.

Well nothing is going to stop dents, since you have to apply the cushioning on the side that sees the force (the outside), all it would do is fill in the inside of the bike, probably giving it some added stiffness. Might be a good way to add some stiffness to a "whippy" titanium frame.

Well you could stop dents to some degree if you covered the outside of the frame with the same rubber used in superballs! Or get Saturn to build a plastic bike.

Car (performance)guys have done this for a while in monocoque structures where there is a hollow "beam" running fore/aft or side to side. I have seen stuff written up claiming from 20% to 300% increase in stiffness depending on the type of foam used and it is made just for this purpose.

Rev. you beat me to it. I know alot of autocross racers use foam to fill the frame rails. The main purpose is to stiffen the HOLLOW frame. It does work but theres one major drawback. It retains moisture. Honda used this technique on some cars in the past. The frames were predisposed to rusting. Once it started there was no way to stop it.

http://www.miata.net/products/chassis/bellco.html

Rev. you beat me to it. I know alot of autocross racers use foam to fill the frame rails. The main purpose is to stiffen the HOLLOW frame. It does work but theres one major drawback. It retains moisture. Honda used this technique on some cars in the past. The frames were predisposed to rusting. Once it started there was no way to stop it.

http://www.miata.net/products/chassis/bellco.html

but if you used it on an aluminum frame...you would be set...

Actually, a hollow tube is much more resistant to bending than a solid tube. Bikes are not bending in half so adding material is not needed.
Not completely true. For a given amount of a given material, a hollow tube is more rigid than a solid bar. The reason is not because the tube is hollow, but because the diameter of a hollow tube of a given weight is much greater than the diameter of a solid rod of the same weight.

That said, I agree foam would do little or nothing for structural integrity. Foam compresses, and the way to increase the structural integrity of a hollow tube is to insert a non-compressible material or structure (i.e. such as honeycomb materials) in the tube.

Look at this page: http://www.itwfoamseal.com/auto_aftermarket.htm

This stuff is used in the auto industry at the manufacturer level as well. A lot of high end cars use it to make the chassis stiffer while keeping it light.

This stuff is pretty non compressible. Once it hardens you can smack it with a hammer and it will barely leave a mark. Calling it foam leaves the impression that it is soft, but it more refers to what it does when you mix the parts and how it looks if you cut it apart with a hack saw. It looks like the minimal expanding foam, in a can, you get at the hardware store but is even tougher.