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My son and I are building him a 24" bike. The frame was donated from a trashed bike, it had a 24" coil suspension fork with 40mm travel and weighed a ton. The axle-to-crown measurement was 435mm.

Now I am looking at some air suspension forks, most of which are 26" but all of them have a axle-to-crown that's much more than the 435mm. I have no experience in this, but I was hoping to reduce the travel on one of these forks such that it has the correct measurement.

Question; would it be likely possible for the fork to be adjusted such that I can reduce the travel more than what is specified on the fork? For example, I am looking at a fork that is listed as adjustable from 100mm to 80mm travel and I would need to adjust the travel down further to 40mm such that I get the required axle-to-crown.

We are using disc brakes so I am only concerned about reducing the crow-to-axle measurement.

example: a 26" fork is listed with axle-to-crown of 490mm and travel of 100mm (adjustable down to 80mm). I am hoping to "hack" the travel down to 45mm such that the axle-to-crown is 435mm.

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    I have written to the sellers of such forks, but I am only getting back original specifications. Sep 7 '20 at 6:34
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    Not an answer to your question, but there are dedicated 24" suspension forks for kids from e.g. Manitou/Hayes. They do cost like middle price ranged "grown-up" forks. Sep 7 '20 at 8:59
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    Have you considered whether a suspension fork is even needed. If you have access to a 26 inch bike see if you son is heavy enough to even get the forks to compress. Most kids bikes I have worked on have zero suspension compression with the child sitting in the saddle.
    – mikes
    Sep 7 '20 at 10:34
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    Alternative approach, can you fit 26" front and rear wheels?
    – Criggie
    Sep 7 '20 at 20:03
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    @Criggie 26" wheels would in our case not be possible for two reasons: standover height and frame spacing. Sep 8 '20 at 4:00
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The fork's travel is often regulated by adding/removing or repositioning plastic bottom out and/or top out tokens of fixed height inside the fork. For such a system, one can reasonably assume that two following possibilities are most common.

  1. A decrease of, say, 10 mm of travel is accompanied by exactly 10 mm decrease of axle to crown height. All moving parts of the fork are just getting shifted up by the same distance.

  2. A decrease of 10 mm of travel results in 0 mm of AC length change. This may be the case when the fork's construction decouples travel adjustment from AC adjustment.

It would be less reasonable to expect a 10 mm of travel change to cause an unproportional decrease to AC — where would additional millimeters go to? Again, it should be possible to imagine/make such a fork, but it would not be a feature used/requested by many customers.

In your case, it may be more realistic to try simultaneously reducing both the travel and the AC distance by 50 mm (2"), from 100 mm to 50 mm, thus achieving the desired AC distance and still keeping some of the travel. However, other aspects of the fork's construction may interfere with your plans. It is impossible to say for certain without looking at how it is made inside.

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  • Thanks @Grigory Rechistov, I would not expect to reduce the axle-to-crown with more than I had wanted to reduce the travel. So I want to reduce the travel with 60mm and hope the axle-to-crown to be reduced with 60mm as well. I'll edit my question to make clear I want to reduce the travel more than what its specification. Sep 8 '20 at 4:02

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