Bicycle Mechanics - question on swapping out forks

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muteseh
03-14-06, 12:47 PM
I'm in the process of converting my mtb ('00 Gary Fisher Aquila, frame size XL) into a commuter and was wondering what I need to know about swapping out forks. That is, I'm switching out the rockshox jett sl for a mid 90s GT Timberline cromoly fork and was wondering what I need to know and do.

spunkyruss
03-14-06, 06:09 PM
Do the junk fork and the replacement fork both use the same type of headset (i.e., both threaded or both threadless)?

Do the junk fork and the replacement fork both have the same steerer tube outside diameter (i.e., both 1" or both 1 1/8")?

Is the steerer tube of the replacement fork long enough to work with your frame?

Changing forks may change the geometry of your bike a bit. If I'm not mistaken, many manufacturers starting producing "suspension corrected" frames in the mid 90s, so it might not even be an issue.

If the anwers to the first three questions are "no," then you'll have to beg, borrow, or steal some additional parts. I honestly don't think that I know enough about geometry to assist you much in that area.
muteseh
03-14-06, 06:14 PM
yeah i figured out that the answers to 1 & 2 are no

thx

tonyt
03-14-06, 11:19 PM
Changing forks may change the geometry of your bike a bit. If I'm not mistaken, many manufacturers starting producing "suspension corrected" frames in the mid 90s, so it might not even be an issue.

If the anwers to the first three questions are "no," then you'll have to beg, borrow, or steal some additional parts. I honestly don't think that I know enough about geometry to assist you much in that area.

Measure the distance on each fork from the center of the dropouts to the bottom of the surface where the lower headset bearing race seats. If they are the same the geometry will be the same.

Early rigid forks are ca 390 mm. "Suspension corrected" rigid forks come in various lenghts (longer than 390 mm) depending on the travel of the fork they replace.

I had to special order a 418 mm fork from Vicious Cycles for an early Bianchi MTB (light weight steel frame, lugged Columbus tubing) I converted to rigid as it has a 1 inch steerer tube and corrected forks in 1 inch are rare as hens teeth.