Framebuilders - Extending Steerer Tube?

I'm quite tall and I've got a custom MTB frame that has a really long head tube. When I asked the builder to make me a frame with the head tube length I wanted (to get the bars where I wanted them), the builder warned me that it might be difficult to find a suspension fork for the frame. At that time (five or so years ago) Marzocchi supplied their forks with an uncut 280mm steerer tube (which was just barely long enough) and I already owned a new, uncut Marzocchi fork so I asked the builder to go ahead with the build. I ran that fork up until this year but now it's shot... destroyed really (long story).

I'm finding that the "new" suspension forks come with steerer tubes that are about 265mm or less. None of them fit my frame. I've already e-mailed all of the fork manufacturers to see if they can provide me with a special fork. White Bros. can supply me with a fork with an extra long steerer tube but it'll cost me $750 and I really don't know if I want to spend that much. I can find rigid forks (both custom and production) with long enough steerer tubes but I'm not sure I want to go full rigid.

Anyway to get to the point... I'm wondering if a frame builder or skilled welder could weld an extension onto a steerer tube while keeping it straight enough so that the headset would be properly aligned. I've already drawn-up a machined extension (I'm mechanical designer), had it fabricated and tried using Loctite and roll pins to extend a fork as an experiment. But despite appearances, the extension isn't perfectly straight so the headset binds. That and the extension works itself loose.

Does anyone have any thoughts or suggestions? Should I just say screw it and go with a rigid fork?

get a rigid fork, at least until you an figure out a different solution. maybe take the steerer out of a susp. fork and replace it with a longer one. that might only cost a few hundred dollars for the labor of removal and reinstall. but i don't know much about suspension forks.

Does anyone have any thoughts or suggestions? Should I just say screw it and go with a rigid fork?[/QUOTE]


A certified welder can add your entension without comprimising strength and reliability. All I would suggest is to use TIG and add a reinforcing tube behind the weld. Remember that most bikes are held together with welding or brazing.

Mike

the issue with the extension isn't so much strength as straightness. if you could make sure the existing steerer tube and the extension both had perfectly flat ends that are going to but together, it could work. and like he said, a reinforcing tube inside the steerer at the weld.

if it were me, i would find i fork that i could drill the old steerer out (take it to a machine shop), and then just put in a new one. it would be a little pricey, but cheaper than $750.

I'm taking it that the fork is threadless and you need 280mm so it has some extension. You might want to see if you can convert to a threaded fork. The 265mm forks might be long enough to fit a threaded headset. You can use a 1 1/8" quill MTB stem then. You will actually be able to bet the bars a lot higher with the quill than the threadless. Good luck

Tim

the issue with the extension isn't so much strength as straightness. if you could make sure the existing steerer tube and the extension both had perfectly flat ends that are going to but together, it could work. and like he said, a reinforcing tube inside the steerer at the weld.

if it were me, i would find i fork that i could drill the old steerer out (take it to a machine shop), and then just put in a new one. it would be a little pricey, but cheaper than $750.

I agree that the issue is with keeping the extension straight. The machined extension that I had made is pressed (lightly) into the steerer tube and then roll-pinned in place. I also applied Locktite (for press fits) to the "male" part of the extension before pressing it into the fork. You would think that the press fit would ensure that it's perfectly straight and it appears to be. But when you preload the headset and clamp the stem to the extension you can see that the headset isn't aligned properly and it's impossible to adjust the headset to both remove play and keep it from binding. A good weld is as strong as the parent material so I'm not concerned about the strength of the material. If I buy a new suspension fork, have a welder add an extension and it's not straight, my only option would be to cut-off the extension and either try again or sell the fork on eBay for a loss. The more I think about it the more I think I'll just put a rigid fork on the bike.

I'm taking it that the fork is threadless and you need 280mm so it has some extension. You might want to see if you can convert to a threaded fork. The 265mm forks might be long enough to fit a threaded headset. You can use a 1 1/8" quill MTB stem then. You will actually be able to bet the bars a lot higher with the quill than the threadless. Good luck

Tim

Yeah it's threadless. I've thought about trying a threaded fork but the problem is that the threaded ones have shorter steerer tubes. You could try to thread an unthreaded steerer but almost all of the "good" forks come with aluminum (or carbon) steerer tubes. Only the real cheapies come with steel steerers these days.

The probelm with getting a fork and having a new steerer installed is that almost all steerers are press fit these days. Very, very few (if any) are clamped in with screws anymore. And if you do find an older fork with a triple clamp crown, you'd still have to have a long steerer tube custom machined for you because they're not available commercially. A steerer tube is more than just a hunk of tubing. There are two tightly toleranced diameters at the fork crown, one for fitting it into the crown and one for pressing on the fork crown headset race. That and the O.D. of the tube itself needs to be held close to 1.125 for the headset to fit etc.