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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 10-08-10, 09:49 AM   #1
whitekimchee
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Forks

Is there a specific difference in performance between a straight fork, slightly curved fork, or a uni crown fork? Is it just aesthetics? I was just curious about this.
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Old 10-08-10, 10:01 AM   #2
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There is no meaningful difference other than aesthetics. Given the same specs (offset, length), they should handle the same. A curved fork might be a little more forgiving on bumps, a straight fork might be a little stiffer.
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Old 10-08-10, 11:14 AM   #3
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The more your front wheel is directly beneath your handlebar, the twitchier your steering will be, basically making your bike more agile. The further forward your front wheel is, the more stable at higher speeds.
This is of course a very simplified explanation.
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Old 10-08-10, 11:48 AM   #4
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The more your front wheel is directly beneath your handlebar, the twitchier your steering will be, basically making your bike more agile. The further forward your front wheel is, the more stable at higher speeds.
This is of course a very simplified explanation.
This I know. I was curious as to whether or not the design of the fork itself had anything to do with the feeling of the ride regardless of it's placement on the frame
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Old 10-08-10, 12:51 PM   #5
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Originally Posted by shenny88 View Post
The more your front wheel is directly beneath your handlebar, the twitchier your steering will be, basically making your bike more agile. The further forward your front wheel is, the more stable at higher speeds.
This is of course a very simplified explanation.
This is actually completely wrong. The more rake you have in relation to the angle of the head tube (which decreases trail), the more twitchy it will be. Road bikes generally have head tube angles between 71 and 73 degrees, so forks with higher rake (40-45mm) offer optimal steering and stability. Track bikes, on the other hand, have head tube angles of 74+ degrees, so 30-35mm rake forks are necessary to make them handleable. If I put a 44mm rake road fork on my 75 head tube track frame, I wouldn't be able to ride in a straight line. If you look at the old motorpacing bikes from back in the day, you'll notice that the fork looks backwards in order to have a huge amount of trail to make them very stable, because those guys are going 50mph+.





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Old 10-08-10, 12:54 PM   #6
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Originally Posted by whitekimchee View Post
This I know. I was curious as to whether or not the design of the fork itself had anything to do with the feeling of the ride regardless of it's placement on the frame
To answer your question, curved forks are slightly more compliant and straight forks are slightly stiffer, but it's hard to tell. Fork material generally has much more of an effect on stiffness.
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Old 10-08-10, 06:38 PM   #7
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nice nice thanks for the info
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Old 10-08-10, 06:51 PM   #8
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theoretically everything said is true, and that unicrown is lighter.

practically, however, it depends on the fork. you can make a unicrown heavier than a lugged, you can make a curved stiffer than a straight. i would venture to say that the higher quality the fork, the more it will adhere to its theoretical advantages... and the cheaper/lower quality the fork, the more it will try to look like a specific aesthetic while disregarding performance characteristics adherence to design.
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Old 10-09-10, 04:25 AM   #9
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Yes it is counter intuitive, but you do have that completely backwards. mrvile has a decent explaination of that.

Moral of the story: if you want to replace your fork, make sure you get the same offset within +/-5mm. Realistically, most people won't notice a difference of less than 5 mm offset (but those of you who will know who you are).

Also, a fork that gets its rake by curve near the hub is going to be a little more forgiving of bumps than one that is mostly straight.
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Old 10-09-10, 08:14 AM   #10
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Just me, but it's aesthetics. Straight forks have the rake angle designed into the point where the bottom of the head tube of the frame and fork are. A curved fork is straight coming out of the bottom of a head tube of the frame and the rake is created with the curvature. The angle of a straight fork and the curve of the curved fork can effectively create the same wheel base.

A longer wheelbase is more stable at higher speeds, so flipping the fork backwards like that decreases stability because the wheelbase of the bike is shorter. And for frame geometry and head tube angle, just research that, track bikes have varying angles that may be 74*, but for the most part, there are track frames all over the place that are 72-74*, that's more dependent upon frame size. A shorter wheelbase improves steering, steering = turning, and a vehicle/bike with a shorter wheelbase has a shorter turning distance. It only makes sense, a unicycle has effectively a zero wheelbase, it's comparatively unstable and twitchy to steer and ride at higher speed in comparison to bikes with longer wheelbases. So many other factors effect the responsiveness of a bike, even tire pressure. A bicycles frame geometry, material composition is a complete system that combined with the forces of nature determine a bike's handling manners. In that regard, I couldn't say which fork is better.

Road Bike:

http://www.fujibikes.com/bike/details/altamira_ltd

Track Bikes:

http://www.fujibikes.com/bike/detail...sic_track_life
http://www.fujibikes.com/bike/details/declaration
http://www.fujibikes.com/bike/details/feather

Wheelbase & Stability:

http://www.dclxvi.org/chunk/tech/trail/
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Old 10-09-10, 07:13 PM   #11
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I would argue that more rake is more forgiving for bumps. Hence hetchins curvy stay design.
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Old 10-10-10, 08:26 AM   #12
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I would argue that more rake is more forgiving for bumps. Hence hetchins curvy stay design.
Forgiveness for bumps is more a function of shock absorber forks. The rest of us have solid forks and whatever the material is determines how much flex it'll have. With that, the width of tires and air pressure also effect forgiveness, probably more so than anything else as that becomes the shock absorber in the absence of one built into the forks. I've found that with the solid forks, a freshly paved asphalt road is the most forgiving surface, smoothed concrete is also a nice ride, yet the expansion joints can be jolting still.

And it's also nice to have rear shock absorber(s) too.

Last edited by fuji86; 10-10-10 at 08:33 AM.
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