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PostPosted: Fri Oct 30, 2020 11:32 am 
Dirt Disciple

Joined: Thu May 05, 2016 5:28 pm
Posts: 98
Location: Urmston, Manchester
In this article:

https://en.wikipedia.org/wiki/Bicycle_poverty_reduction

Almost every bicycle has a pair of rails from the fork dropout to the steerer, with a pair of springs at the top. What are these for?


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PostPosted: Fri Oct 30, 2020 12:42 pm 
Retro Guru

Joined: Sun Jun 10, 2012 9:49 am
Posts: 445
Location: Hampshire
I think they're brake drop compensating springs used to alter the angle of attack of the brake block in relation to the rim while riding on extremely bumpy terrain...or I may have got this complety wrong and I'm totally baffled.. :|


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PostPosted: Fri Oct 30, 2020 12:52 pm 
Dirt Disciple

Joined: Thu May 05, 2016 5:28 pm
Posts: 98
Location: Urmston, Manchester
I was wondering if they're some kind of reinforcement, to reduce the amount of bend on the forks as the bike carries more than it was designed to.


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PostPosted: Fri Oct 30, 2020 2:27 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 10319
Location: New Forest, UK
They are meant as a kind of reinforcement and suspension. Do they work? No. It's just a fashion, like doubled top tubes which are also common. You see them on utility bikes in China too.


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PostPosted: Fri Oct 30, 2020 2:38 pm 
Dirt Disciple

Joined: Wed Aug 05, 2020 9:03 am
Posts: 52
Location: Worcestershire
I agree it's principally fashion; as is debated often on this site, fashion dictates an awful lot of what we regard as normal. If XTR stuff is pearl-white in 2022, then the 2024 Carrera range will have white chainrings...


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PostPosted: Fri Oct 30, 2020 4:21 pm 
retrobike rider
retrobike rider
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Joined: Tue Jan 29, 2008 11:04 pm
Posts: 2583
Location: A wretched hive of scum and villainy...
They are fork reinforcements/braces.

Generally not needed on forks made of decent chrome molybdenum or such, and are pretty much just fashion on modern girder forks such as Jones, Stooge or Black Sheep, but if you have some cheap forks made of mild steel, there is a considerable risk that the vertical loadings will overcome the yield strength of the material, and they will permanently deform (Bend), rather than just springing back.

This could be sorted by using a really thick wall in the fork blades, but that will ruin the ride quality and be harder to manufacture. So the braces are a compromise.
They are generally in straight compression & tension (rather than bending/bowing) as the fork blades flex, so can help the fork blades take higher loads by mechanically limiting the extremes of flex, thus preventing the fork material from going above its yield point and permanently bending.

All the best,


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