Trek 850 SHX Rigid fork conversion
09-16-20, 08:05 AM
#1
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Trek 850 SHX Rigid fork conversion
Does anyone have any experience with swapping out suspension forks for rigid ones? I'm picking up a 93 Trek 850 SHX and would like to go down the rigid gravel bike route.
09-16-20, 09:49 AM
#3
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Join Date: Feb 2017
Location: Maryland
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Bikes: '73 Raleigh Competition, Guru Sidero, Soma Groove, Smolenski,
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I am assuming this is a mountain bike with 26" wheels?
I did this to an early '90s Smolenski (custom builder out of Grand Rapids) mountain bike with a Halson Inversion fork on it. I removed the Halson (I should have kept it, but I think it ended up in the trash) and replaced it with a rigid fork. https://www.jensonusa.com/Dimension-...n-Fork-en.aspx pretty sure it was that, but in a 1" steerer. It is shorter than the old halson, so it steepened the steering tube angle, making an already fairly quick steering mountain bike a bit twitchy. Fun in the twisties, a little terrifying on steep, rocky descents.
You have a few options, the trick is the dropout to crown length and understanding how an change in that measurement changes the steerer tube angle, and thus, the steering and trail requirements. There are several resources to help compute trail (imaginary distance between where a straight line from the steerer tube would contact the ground vs. the actual contact) https://calfeedesign.com/geometry-of-bike-handling/ is a decent primer on the subject.
If you wish to maintain handling, a dropout to crown distance and fork rake that are the same to the current fork will be necessary, Common practice is to measure the dropout to crown with the fork at it's proper sag when you sit on it, about 1/4 to 1/3 of fork travel. i'm guessing on a mountain bike from 1993, we are talking about 75-80mm of travel? so about an inch of sag.maybe a touch less, be that depends on how you like it setup.
Likely scenario is that the fork linked is shorter than you measurement, and other rigid forks are about 440mm, although this may have changed in the ~13 years since I did this. I was also limited to 1" steerers and 1-1/8" are more common and may give you more options. You can always spend $$$$ (or ££££ in your case) and have a custom one made.
If your headset/fork/stem is threaded (quill) now is a good time to convert to threadless. Finding any of these forks already threaded will likely be impossible, which would require you to find a shop to thread them, which may or may not be worth it (I would say it;s not, but only you can know how to spend your money).
Hopefully that helps some.
I did this to an early '90s Smolenski (custom builder out of Grand Rapids) mountain bike with a Halson Inversion fork on it. I removed the Halson (I should have kept it, but I think it ended up in the trash) and replaced it with a rigid fork. https://www.jensonusa.com/Dimension-...n-Fork-en.aspx pretty sure it was that, but in a 1" steerer. It is shorter than the old halson, so it steepened the steering tube angle, making an already fairly quick steering mountain bike a bit twitchy. Fun in the twisties, a little terrifying on steep, rocky descents.
You have a few options, the trick is the dropout to crown length and understanding how an change in that measurement changes the steerer tube angle, and thus, the steering and trail requirements. There are several resources to help compute trail (imaginary distance between where a straight line from the steerer tube would contact the ground vs. the actual contact) https://calfeedesign.com/geometry-of-bike-handling/ is a decent primer on the subject.
If you wish to maintain handling, a dropout to crown distance and fork rake that are the same to the current fork will be necessary, Common practice is to measure the dropout to crown with the fork at it's proper sag when you sit on it, about 1/4 to 1/3 of fork travel. i'm guessing on a mountain bike from 1993, we are talking about 75-80mm of travel? so about an inch of sag.maybe a touch less, be that depends on how you like it setup.
Likely scenario is that the fork linked is shorter than you measurement, and other rigid forks are about 440mm, although this may have changed in the ~13 years since I did this. I was also limited to 1" steerers and 1-1/8" are more common and may give you more options. You can always spend $$$$ (or ££££ in your case) and have a custom one made.
If your headset/fork/stem is threaded (quill) now is a good time to convert to threadless. Finding any of these forks already threaded will likely be impossible, which would require you to find a shop to thread them, which may or may not be worth it (I would say it;s not, but only you can know how to spend your money).
Hopefully that helps some.
