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Old 04-08-11, 10:55 AM   #1
beebe
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How to buy the same fork twice?

What do I need to look for in a new fork to make sure that it gives my bike the same handling characteristics as the old (now busted) fork gave it?

In other words: will all straight-bladed, steel, threadless, 1 and 1/8 inch, 700c, forks be the same, ignoring build quality?
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Old 04-08-11, 11:14 AM   #2
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Close, but not necessarily identical. Besides the key items like wheel size and steerer diameter and lenght, there are other variations.

1- wheel/crown clearance. Often measured as axle to crown dimension, or sometimes as brake reach for a given wheel.
2- rake, or the distance forward of the steering axis of the front axle. On 700c forks this is usually 40-50mm.
3- braze-ons and other fittings including for canti or V-brakes, or fender eyes, rack mounts, etc.

Then there are the other items like whether the steerer is threaded or not, and for 1" forks the crown seat diameter which may be ISO, 26.4, or JIS, 27.0 or not machined and needing prep.
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Old 04-08-11, 12:48 PM   #3
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Quote:
Originally Posted by FBinNY View Post
Close, but not necessarily identical. Besides the key items like wheel size and steerer diameter and lenght, there are other variations.

1- wheel/crown clearance. Often measured as axle to crown dimension, or sometimes as brake reach for a given wheel.
2- rake, or the distance forward of the steering axis of the front axle. On 700c forks this is usually 40-50mm.
3- braze-ons and other fittings including for canti or V-brakes, or fender eyes, rack mounts, etc.

Then there are the other items like whether the steerer is threaded or not, and for 1" forks the crown seat diameter which may be ISO, 26.4, or JIS, 27.0 or not machined and needing prep.
The OP has already answered several key points for this, he needs a 1 1/8th 700cc fork

What was the fork you orginally had / bike it was from? have you done a google search for it as you may be able to get an exact replacement.

For things like the (a)headset, do you have the old crown race, if not, then you need a new headset if a crownrace can not be sourced.

For build / feel, would need to know if yours was Hi-ten, Cromo, Double butted etc. as the type of steel will make a difference here.

How did it fail as well, as I don't think you want that characteristc as well in the few fork
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Old 04-08-11, 01:51 PM   #4
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To answer the OP's question, no they are not all the same.

Where handling is concerned rake offset and crown to axle length are the variables to consider. Increasing rake offset decreases steering trail and can make steering feel quicker, even twitchy. Decreasing rake offset increases steering trail causing the bike to have more of a tendency to continue in a straight line. I can confirm that a 3 mm change in rake offset can make a significant difference. In my case the change was easy to get use to after a few rides.

Head tube angle is the other big variable controlling steering trail. HTA built into the frame cannot be changed after the frame has been built. Many manufacturers use different HTA's with different frame sizes. Rake offset can be used to offset the differences in HTA's. Fork length, crown to axle, has some effect on the head tube angle. A longer fork will reduce HTA increasing steering trail.

If you cannot find the rake offset of your old fork something in the range of 40 to 43 is a good guess.

Whether the fork legs are straight or curved makes no difference to handling. A fork with straight legs simply has more angle change at the crown.

Last edited by Al1943; 04-08-11 at 02:08 PM.
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