Extending Carbon Steerer Tube!

[DODDY]

Hi,

Just got a bargin set of Carbon Forks :-) The down side is that they are too short in the steerer tube by about 25mm. Has anyone ever 'extended' a carbon steerer tube or has any idea how this could be achieved. I am in the engineering business and have access to quality aluminium and all the tools to manufacture an extension tube the correct sizes. Can you bond a stepped tube to the top of the carbon. Could I extend the steerer with a sleeve and use the stem to hold it all together. This is for a road bike, if that makes any difference.

 

[gbb]

I'm in engineering too and having looked at steerers....i cant say i'd fancy trying, just from a safety / strength point of view.

 

[HeartAttack]

Sorry I wouldn't want to ride with an extention to the steerer.

Its only a bargin if the item/forks are suitable and usable and in this case their not and so you have wasted your money

 

[Globalti]

I disagree. If bike frames are built from ali or carbon tubes bonded to lugs it should be possible to make a very strong joint. In the case of a steerer tube it would be sufficent to choose or machine a steel or ali liner to fit snugly inside the steerer and then fit an extension on top of it. Everything could be bonded together with a resin glue and the result would be stronger than the original steerer. In any case the major point of bending moment on a fork must be at the bottom bearing seat. The further you move awy from that point the lower the leverage exerted by braking forces and road shock.

The hardest part will be in ensuring you can achieve a good uniform layer of adhesive between the steerer and the inner sleeve. You might need to find quite a liquid glue or assemble with everything warm to ensure an adequate fill.

Do it, I'd say, but test the setup in a rig before riding for peace of mind.

 

[numbnuts]

I’m with Rigid Rider all you need a a stepped tube, I spent a few years as a fibreglass laminator for the M.o.D. and have seen jobs like this done on warships

 

[accountantpete]

Can't you just pop a Raiser in the top?

 

[Globalti]

The last warship that Numbnuts repaired:

 

[Chrisz]

The last SUBMARINE that Numbnuts repaired:

 

[gbb]

I disagree. If bike frames are built from ali or carbon tubes bonded to lugs it should be possible to make a very strong joint. In the case of a steerer tube it would be sufficent to choose or machine a steel or ali liner to fit snugly inside the steerer and then fit an extension on top of it. Everything could be bonded together with a resin glue and the result would be stronger than the original steerer. In any case the major point of bending moment on a fork must be at the bottom bearing seat. The further you move awy from that point the lower the leverage exerted by braking forces and road shock.

The hardest part will be in ensuring you can achieve a good uniform layer of adhesive between the steerer and the inner sleeve. You might need to find quite a liquid glue or assemble with everything warm to ensure an adequate fill.

Do it, I'd say, but test the setup in a rig before riding for peace of mind.

What you say in essence is true....it could or can be done. I'd thought about what you could bond it with..metalset, epoxy resin etc etc. The trouble is, it would probably be ok...but what good's probably.

Even if you tested it, it wouldnt be a proper test. You're right, i'd imagine most (if not all) the force is at the base of the steerer, but if you set it up and applied some force to it and it stayed put...how do you know whether it didnt weaken it while testing, to fail at some point in the future.

I'm thinking as i'm writing...no, i think you're right. I missed the point it was only and extension of 25mm at the top. The only force it has to take is rotational, and not much at that. Thats because the original steerer (i assume) will still be supported correctly at the top and bottom. As the extension is only 25mm, the joint would be clamped by the stem anyway. That'd help support it as well.

I guess if you have the equipment and materials doddy...it would be interesting to try.

 

[Globalti]

If you do it, can you post a few pics on here?

Actually if the joint was above the top bearing I would worry more than if it was below because this would put it fair and square at the bottom of the stem where it was at the point of maximum stress from the handlebars.

 

[rogersavery]

if you only need 25mm why not either turn the stem upside down (assuming it is installed the lowest way at the moment) or get a adjustable stem

 

[numbnuts]

The last warship that Numbnuts repaired:

Actually that’s not funny just before the Falklands war I worked on fitting new stainless steel door handles to all the fire doors on the Sir Galahad, it never came back, I was working for Husbands Shipyard at the time

 

[SimonC]

What you say in essence is true....it could or can be done. I'd thought about what you could bond it with..metalset, epoxy resin etc etc. The trouble is, it would probably be ok...but what good's probably.

Even if you tested it, it wouldnt be a proper test. You're right, i'd imagine most (if not all) the force is at the base of the steerer, but if you set it up and applied some force to it and it stayed put...how do you know whether it didnt weaken it while testing, to fail at some point in the future.

I'm thinking as i'm writing...no, i think you're right. I missed the point it was only and extension of 25mm at the top. The only force it has to take is rotational, and not much at that. Thats because the original steerer (i assume) will still be supported correctly at the top and bottom. As the extension is only 25mm, the joint would be clamped by the stem anyway. That'd help support it as well.

I guess if you have the equipment and materials doddy...it would be interesting to try.

Would it not have a bending force on it from body weight on the handlebars pushing the stem down, with the new 25mm bit right at the pivot point. I would have thought it would take a bit of hammer, especially downhill when your weight is pushed forward and is taken by the handlebars.

Might have been cheap forks, but might not be the point when your face is rubbing on the tarmac I wouldnt fancy it myself.

 

[MartinC]

Would it not have a bending force on it from body weight on the handlebars pushing the stem down, with the new 25mm bit right at the pivot point.

This is the important bit. There's a limit to how much unsupported (i.e. outside of the span of the headset bearings) steering tube it's sensible to have because of the leverage that get's applied to it. I wouldn't be too happy putting more than 25-30mm worth of spacers on carbon steerer let alone making a home made extension to one. Neither would I put a standard non threaded steerer tube extension on one. Flipping the stem is the best approach.

 

[gbb]

Would it not have a bending force on it from body weight on the handlebars pushing the stem down, with the new 25mm bit right at the pivot point. I would have thought it would take a bit of hammer, especially downhill when your weight is pushed forward and is taken by the handlebars.

Might have been cheap forks, but might not be the point when your face is rubbing on the tarmac I wouldnt fancy it myself.

The more you think about it, the more questions it raises. Technically, it's quite do-able. Its not that much different to fitting an quill to Ahead adapter...if the inserted length's long enough to give it strength and a decent bonding area.
Ultimately, it sounds do-able...but i still wouldnt try it on my bike. I'd sooner ebay the forks and get the proper ones.
But if OPs willing to try....i can't see why not.