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Road Bike Fork Sizing

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Road Bike Fork Sizing

Old 07-26-10, 02:02 AM
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Road Bike Fork Sizing


So I'm confused by fork sizes and where to start in a bid to replace them. There's a strong possibility that I'm about to ask a stupid question?

I'm replacing a frame (bianchi via nirone 7 C2C) but want to retain as many components as possible. The two parts causing most confusion are seat post and forks.

Seat post I now realise must be replaced, I can find the sizing for the Bianchi and all seat posts I've seen for sale are sized.

I was told that forks sizes are also difficult to match, however I can no more find a size for my forks, than I can find out what size a potential new part would be or what size of fork the new frame is supposed to take. My instinct tells me this means that there isn't much if any variation in road bike forks sizes.

The only fork measurement I have found is the Fork Rake, and while this is important doesn't seem to me significant if I want to continue using the old ones.

So my question to any experts out there would be how do I find out what size my forks are? If none of the forks available for general resale are sized then how do I find the right ones for my new frame?

Cheers FlyerSc
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Old 07-26-10, 05:04 AM
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there are standards:
1" normal and 1 1/8" oversize

Many new bikes have oversize fork (that is the diameter of the steerer tube)

The basic thing you have to look at is match the standard 1", or 1 1/8" (or other oddballs 1 1/4, etc), and check for the height of the steerer tube (height of the head tube). The steerer tube can be cut, and can be threaded further more (for threaded forks), but it won't fit in a longer head tube.

As I can see bianchi via nirone 7 C2C has 1 1/8" oversize non-threaded fork, with a relative short steerer tube (head tube)
You need to check the length of the head tube to be shorter than the length of the steerer tube of the fork (plus ~40mm to fit the stem)
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Old 07-26-10, 05:15 AM
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Great stuff Asi,

that was exactly the kind of clear and concise info i've been looking for.

very much appreciated and if you're interested i'm reasonably sure my forks are transferrable with my preferred frame... which means i'm in a fairly good mood now.

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Old 07-26-10, 08:49 AM
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With road bikes they are all similar enough that you don't need to worry about anything other than that the steer tube is long enough. If it were a mountain bike then you need to worry about the length of the legs as well as the length of the steer tube.
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Old 07-26-10, 09:46 AM
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Then there is the issue of Trail, the difference ... on the ground between the line thru the head tube ,

and, the vertical thru the axle, the contact with the ground,

Its changed by fork offset, crown offset or bend in the blades. or a combination..

Plunger tubes on suspension fork I have is offset at the fork crown, ahead, and there is another offset , the dropouts in the bottom casting are ahead of the stanchion tubes in the offset fork crown.

so that is a combination of 2 offsets..


Vintage Bike Quarterly goes on at length on low trail front loaded designs ,

and higher trail geometry Like for carrying pannier load on the back, primarily.

Last edited by fietsbob; 07-26-10 at 09:50 AM.
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