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Old 11-06-07, 09:11 PM   #1
pengyou
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Replacing fork - how do I measure it?

I want to put a stronger fork on my bike. How are forks measured/sized? I know the wheel size is important but what else?
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Old 11-06-07, 09:22 PM   #2
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Forks are measured with axel to crown length, travel, rake, trail, steerer length etc.
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Old 11-06-07, 09:59 PM   #3
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I want to put a stronger fork on my bike. How are forks measured/sized? I know the wheel size is important but what else?
steer tube length = head tube + HS stack height.

ed rader
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Old 11-06-07, 10:09 PM   #4
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steer tube length = head tube + HS stack height.
+ stem height + spacers - 2 or 3 mm (for threadless systems)
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Old 11-06-07, 10:17 PM   #5
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pengyou: what kind of fork is it--rigid or suspension? threaded or threadless?
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Old 11-06-07, 10:18 PM   #6
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Wow! It is not as easy as I thought. Are some measurements more critical than others?
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Old 11-06-07, 10:19 PM   #7
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It is a rigid fork. I am not sure about the threaded or threadless yet. I will have to take a look.
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Old 11-06-07, 11:03 PM   #8
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First thing, you have to make sure it's threaded or threadless. Look here: http://sheldonbrown.com/gloss_ha-i.html#headset Which does yours look like?

More modern bikes are generally threadless, if that is the case, you need to determine whether it is 1" or 1-1/8". Unscrew the top cap and measure the steerer tube width.

Now for the steerer tube length. If it will be a new fork, it will come with a way long steerer, have it cut (probably to the length of the current one--though you have an option to go longer or shorter) and install the star-flangled nut (what the top cap bolt screws into to compress the headset).

For a rigid fork, the hub axle to fork crown length is not too important as long as the forks were meant for the same kind of wheels (700c, 26", etc.). There is also rake (the offset of the axle dropout from the imaginary line coming down and inline with the steerer), which affects trail... But that might all be more complicated than necessary for you.

Is this a mountain bike or road bike, by the way?

Last edited by JiveTurkey; 11-06-07 at 11:08 PM.
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Old 11-07-07, 01:05 AM   #9
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It is a beach bike. I want to install a hub motor on the fork so I want to make sure the fork is strong enough. Now, I think it is just common steel.
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