Replacing Rigid forks with sus forks



davebee

New Member
Jan 15, 2004
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Hi and sorry if this has been done before.

I currently have a pair of rigid forks on my battered old bike which are using a 1 1/8" threaded headset and a quill stem. Basically I want to rip all of that off and replace it with a suspension fork with 85mm travel, a 1 1/8" AHeadset and some sort of AHeadset stem.

I have ordered a pair of Marzocchi MX Comp (2004) forks which have a 1 1/8" steerer tube and am a little bit worried that they might not fit. I haven't worked out what headset to use. probably a Cane Creek C2/S2 or FSA pig. Something along those lines anyway.

First question, will the headset and the fork phsyically fit on the bike?

Second question. How can I tell if the frame has been built with suspension correction as I am a little concerned the geometry might change significantly.


Third question. If the geometry does change can I "bodge" it by using a stem which has less of an angle than my current one? the current one has something like a 15 degree rise and I was thinking of putting on something closer to 5 degrees to correct any change due to the fork.

Would the above work or have I gone wrong somewhere?


Thanks for your help.

Dave
 

boudreaux

New Member
Oct 16, 2003
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davebee said:
Hi and sorry if this has been done before.

I currently have a pair of rigid forks on my battered old bike which are using a 1 1/8" threaded headset and a quill stem. Basically I want to rip all of that off and replace it with a suspension fork with 85mm travel, a 1 1/8" AHeadset and some sort of AHeadset stem.

I have ordered a pair of Marzocchi MX Comp (2004) forks which have a 1 1/8" steerer tube and am a little bit worried that they might not fit. I haven't worked out what headset to use. probably a Cane Creek C2/S2 or FSA pig. Something along those lines anyway.

First question, will the headset and the fork phsyically fit on the bike?

Second question. How can I tell if the frame has been built with suspension correction as I am a little concerned the geometry might change significantly.


Third question. If the geometry does change can I "bodge" it by using a stem which has less of an angle than my current one? the current one has something like a 15 degree rise and I was thinking of putting on something closer to 5 degrees to correct any change due to the fork.

Would the above work or have I gone wrong somewhere?


Thanks for your help.

Dave
It will physcially fit. Duno about the frame being built as suspension corrected,but the difference is mainly in the crown to brake boss distance in the fork. You can't 'bodge' a correction in basic geometry with a stem change.
 

Solanog

New Member
Feb 12, 2004
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I put a Marzocchi fork on my bike, replacing the one that came with the bike, since the Marzocchi had more travel (110mm) the bike "grew taller" and now it still fits but the top tube is closer to my nutz :eek: The Marzocchi rides great, mine is a 04 MX Comp W/ETA, just when it was about a year old I change the oil, it was clean and it has no leaks. Great fork, specially if compared with the NSync that came with the bike.
 

cydewaze

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Jun 17, 2004
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I've been in your boat before, and boudreaux is correct about the stem change not helping. For what it's worth, I think an 85mm travel fork is a safe-ish bet if you're not sure about the geometry, because the change will be more exaggerated with a long travel fork. The taller the fork is, the greater the change to your head and seat tube angles.
 

dabac

Well-Known Member
Sep 16, 2003
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davebee said:
Hi and sorry if this has been done before.

I currently have a pair of rigid forks on my battered old bike which are using a 1 1/8" threaded headset and a quill stem. Basically I want to rip all of that off and replace it with a suspension fork with 85mm travel, a 1 1/8" AHeadset and some sort of AHeadset stem.

I've done that kind of switch several times, and it's been discussed here earlier too.
Bottom line is:
Yes it can be done.
Yes it will change the geometry of your bike some.
Yes it will increase the load on the frame some, so you might want to avoid it if you're either very afraid to get hurt, or a heavy guy, or likes to do really big airs.
No, it won't have disastrous influence on handling.
No, it won't collapse the bike during regular use.
 

Conniebiker

New Member
Jan 1, 2005
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I have done and love it in my stuff. 80mm is about as tall as I would go though. Beyond that and the handling turns into a downhill rig. The only frames that would make me reluctant to experiment on this would be the early aluminum race type frames. They tended to have barely enough metal to succede.
That said, most of the fork-leverage for 80mm and less, is hype. There is more force on it when you hit trail obstacles yes. Will it be a lethal increase? No.
You will want a lower stem rise, as there will be a gain in head hieght. The exact sizes of the stem/ahead spacers needed will be up to your experimentation.
 

davebee

New Member
Jan 15, 2004
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Conniebiker said:
You will want a lower stem rise, as there will be a gain in head hieght. The exact sizes of the stem/ahead spacers needed will be up to your experimentation.


I sat down and worked all the angles and lengths required such that the handlebars would be in the same position relative to the saddle as before, and then I made the change. It has worked very well and the bike actually feels a lot of stable and I don't seem to have lost any responsiveness. Now I guess it is just a case of breaking the fork in and away I go!