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Need advice on a mtb fixie conversion

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Need advice on a mtb fixie conversion

Old 08-03-08, 03:44 AM
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drafters65
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Need advice on a mtb fixie conversion

I recently got a 94 stumpjumper m2 fs frame without a fork and i want to convert it into a fix speed. I understand that 700c wheels will fit no problem besides the rear stays being 135mm, so i will probably have to build a wheel for the rear. The front is where i have a question...i know that the brakes wont reach the 700c without the mavic adapters, so i was wondering if i can use a road fork without messing up the handling too much. I think the frame was made for a suspension with little travel...something like 35-45mm? The reason that im considering going with a road fork is because i have a cf one on another bike that i dont mind transfering over. so what do you think guys? any input is greatly appreciated...(flame suit on...just incase)
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Old 08-03-08, 04:19 AM
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I think you are crazy. There are all sorts of things that "can" be done that should never be done.

On the other hand, you might end up with the Frankenbike of the Year award.

BTW- you can just use a bunch of spacers for the rear.

I would not attempt such a bike--- it would be easier starting from a better frameset (or frame). I don't know about a 94 stumpjumper, but most mtnbikes have very different headtubes than roadbikes. Assuming it is threaded, I doubt your road fork will be compatible (threadwise)--- unless you plan to cut new threads.
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Old 08-03-08, 05:20 AM
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sounds like you wont be out too much money on this project. And if it doesnt work you will have some parts you could throw on a new frame. Its not going to hurt anything building that up go for it. as far as handling goes, Look up a trail calculator and enter measurements of the fork and frame angles into it to see what the handling will look like.
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Old 08-03-08, 11:31 AM
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Originally Posted by filtersweep View Post
I think you are crazy. There are all sorts of things that "can" be done that should never be done.

On the other hand, you might end up with the Frankenbike of the Year award.

BTW- you can just use a bunch of spacers for the rear.

I would not attempt such a bike--- it would be easier starting from a better frameset (or frame). I don't know about a 94 stumpjumper, but most mtnbikes have very different headtubes than roadbikes. Assuming it is threaded, I doubt your road fork will be compatible (threadwise)--- unless you plan to cut new threads.
well about the threads...the frame didnt come with a fork or stem so i can basically go either thread or threadless right now...i believe the steerer is an 1 1/8 so my cf fork would definitely work but as for rake and length...well that is the part that im unsure about. I dont think putting a road fork on a mtb is that crazy unless it messes up the handling alot and i dont really care how the bike will look aslong as its rideable (function > asthetics on this "project"). Ive never taken a hub apart so i dont know what you mean by adding a bunch of spacers for the rear...is there a site or a diy page you can link me to? thanks for the nominee...frankenbike award here i come!
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Old 08-03-08, 11:43 AM
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Originally Posted by Jenkinsal2 View Post
sounds like you wont be out too much money on this project. And if it doesnt work you will have some parts you could throw on a new frame. Its not going to hurt anything building that up go for it. as far as handling goes, Look up a trail calculator and enter measurements of the fork and frame angles into it to see what the handling will look like.
yea that was exactly what i was thinking before even thinking of this project. The frame was basically found in the trash (well thats how cheap it was). Like you said if it doesnt work ill just put everything on a new frame. Do you have a trail calculator you can link me to...when i google trail calculator i only see those for motorcycles. thanks!
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Old 08-03-08, 12:22 PM
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I would certainly try although others may tell you not too....the worst that could happen is that you have a bike that handles poorly....that being said it should work especially if the frame was originally intended for a suspension fork(look up the specs of the old fork that was on it and find out the axle to crown height of the fork then measure the road fork that you are thinking about putting on and i they are real close it should be fine)...did the stumpjumpers then still have horizontal dropouts?
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Old 08-03-08, 12:38 PM
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Originally Posted by lbthomps View Post
I would certainly try although others may tell you not too....the worst that could happen is that you have a bike that handles poorly....that being said it should work especially if the frame was originally intended for a suspension fork(look up the specs of the old fork that was on it and find out the axle to crown height of the fork then measure the road fork that you are thinking about putting on and i they are real close it should be fine)...did the stumpjumpers then still have horizontal dropouts?
Im not sure when they stopped having horizontals but the 94s definitely still have them. Ive been having a hard time finding the specs of the bike and specialized's interactive faq is really hard to navigate (im still trying to figure out how to ask a question)

edit: I dont think its horizontal dropouts anymore because i saw my friends 2000 stumpjumper and it had the same dropouts. I thought it was because it was in an angle but i think the slide is way too short to be called a horizontal...maybe i should take a picture and have someone id it.

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Old 08-03-08, 12:49 PM
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Try cyclocross fork - they are longer than road ones. I have done what you attempt with Nashbar fork, MTB frame and 700c cross wheels -[never:almost] finished product
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Old 08-03-08, 01:04 PM
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Originally Posted by vobopl View Post
Try cyclocross fork - they are longer than road ones. I have done what you attempt with Nashbar fork, MTB frame and 700c cross wheels -[never:almost] finished product
the reason why im considering a road fork is because i already have the fork/headset/stem ready to be donated by my road bike. This will also give me an excuse to upgrade those parts on my roadbike also haha. is that a pic of you because i think ive seen it somewhere in this forum before.
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Old 08-03-08, 01:10 PM
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try the road fork and if it makes the bike ride wonky then get something else.

just do it.
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Old 08-03-08, 01:16 PM
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Alrights so I punched in some numbers (71 head angle, 43mm fork rake and 622mm wheel diameter) at Kogswell.com trail calculator and this is the result i got: trail 62mm and wheel flop 19mm. I dont know what this all means but from what ive read in calfreedesigns.com 62mm of trail is "normal" and doesnt say anything about the 19mm wheelflop.
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Old 08-03-08, 01:23 PM
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I have posted this before, no it is not me - the guy there tries to understand why my pedals kept spinning downhill :-)

There is one more thing I have seen done in your case: extending the headtube downwards, similarly to what I did here to the top of the headtube - the lower cup should be press fitted to the extension and the extension should press fitted to the headtube. This should rise the front end and slack the angles.
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