Framebuilders - 1" steerer tube into 1 1/8" fork? help please!
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02-11-09, 11:55 AM
I want to use a 1 1/8" triple tree suspension fork on a bike i'm converting into a tandem which has a 1" steerer tube. I have some play with how much room I have above the lower crown and am debating how to meld the original fork/steerer into the new fork. I could cut the fork off and install a steerer converter underneath to connect the fork to or fit a smaller tube inside the steerer and connect it in the fork with a shim and a screw. I am open to suggestions. I'm trying to put this bike together without spending alot and my metal working skills are limited.
I'd be really wary of doing something like this -- the fork is not a part you want to fail if you're traveling at any kind of speed. When you say "triple tree" do you mean a triple crown fork, or something with a leading link, like the Lawwill or one of those nutty Hannebrinks? In any case, the combination of a high-stress suspension fork, limited metalworking skills, a 1" steerer tube, and a tandem seems like one to be avoided (the perfect storm of fork failures?). At least get a full-face helmet!
02-26-09, 10:17 AM
this seems like a post for the Darwin awards.
every stage of this problem is a great big red flag that will lead to catastrophic failure and or death.
02-26-09, 12:55 PM
don't. thats my .02
By tripple tree, you presumably refer to a motorcycle type fork with three bars in the headtube area. These are really strong units, And I don't see any real Darwin award type issues. There really isn't any reason why the central tube couldn't be swapped out. The problems I see are that you would presumably need to get the axial tube in there with nicely fitted ends, then the crown races would need to be cut, and so forth. That doesn't strike me as dangerous, but it does sound like some neat work would need to be done. If you get really lucky the current axial tube is like a shim for the 1" tube, and you can just braze in or possibly epoxy in the races.
If the current tube is mechanical as TT normally are in the moto world, and you can remove it in total. then you could get some 1" 4130 and sleeve the ends with some tubing with a 1" ID, then braze than in place, turn it down, and you could braze on a race ring, Then true everything up with a lathe. It can be tough to do this kind of thing without reamers, and machine tools.
If you can't get the central tube out, it's a lot messier, and it would help to seel a part to give the right advice. If you have acres of room in there, even epoxy can work.
One issue you need to address before the above is whether the offset of the TT fork is correct for your Head tube angle and the trail figure you need. There are trail calculators all over the net, so that should help. The crown height also needs to be right.
02-27-09, 12:49 PM
Prefer to avoid the darwin award issues. I've included a link to the source the NYCBikes ebay store which is http://myworld.ebay.com/nycbikes/ in case the upload doesn't work or anyone else is inspired.
02-27-09, 12:51 PM
Here a picture of the type of fork I mean.
02-27-09, 03:12 PM
I think you're bigger issue is that you are trying to use incompatible parts in a way that will seriously compromise the structure.
A frame with a 1" headtube is not a frame designed to cope with the extra stress a long triple clamp fork will put on it, and then add the forces from a tandem configuration.
Take a minute and reread Nicolacycles response.
02-28-09, 04:41 PM
The bike I intend to use is a 1960's Raleigh that I imagine is stronger than most mack trucks on the road today. The potential for serious problems should my fork design fail at speed have occurred to me which is why I'm asking questions.
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