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Old 08-25-12, 06:22 PM   #1
chrisreed
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Fat Frames and Straight Forks

I'm an old guy needing to replace a stolen 10-speed drop-handle bike after about 25 years, so I'm a bit out of date. I look at all the bikes around now and I don't understand two things.

1) Why are all the frames so fat and HUGE? All that extra metal must weigh a ton. And it can only add to the cost of manufacture. Certainly the old skinny frames were plenty strong enough. I had plenty of accidents without ever bending the frame. So why on earth would I buy these new tanks?

2) For a hundred years the front forks always had a forward curve at the bottom. This has something to do with stability and tracking and turning freedom. Now all the front forks are perfectly straight. Was everyone wrong for a hundred years? Are they simply the price necessary to have shock-absorbers?

Any help letting me understand the new designs will be appreciated.
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Old 08-25-12, 07:17 PM   #2
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Yes the bikes of today are heavier than ever before. How astute of you to notice.
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Old 08-25-12, 07:43 PM   #3
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Don't listen to those guys, I'll give you the serious answer.

The old steel skinny frames were getting so light the UCI had to enact minimum weight requirements to put a stop to it. Besides the excessive light weights, the frames were getting so skinny that bikes would literally disappear right up riders butts. To combat this, they started to make the frames fatter. But since steel is governed by the laws of Superman, he was in no way going to allow 'steel' to be synonymous with being fat so they had to go to another material.

As for the straight forks...

Well thats just to combat the curvy backsides to keep the bike in neutral handling. If the front was all curvy , some people might unconsciously feel the desire to mount it from the wrong end creating the inverse of the original problem.
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Old 08-26-12, 02:59 AM   #4
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Fat frames are made with low density aluminium. More metal adds very little extra weight. You need fat frames for stiffness to eliminate flex which is bad for aluminum.
The manufacturers have done their math about volume production costs and aluminiumium is cheaper to fabricate than steel at high volumes.
Modern forks are made from carbon fibre and are moulded; you can make them any shape you want. As a designer, you can set up the correct trail and join the bits however you like. Straight blades use less material and are stronger and stiffer.
Old steel forks were manufactured by bending to achieve the trail. Late model steel race forks abandoned the curve and used straight blades welded at the correct angle but still with the same trail or offset.

You can still get old-school steel bikes from Soma, Gunnar, Rivendell, maybe Jamis.

/<Troll fed>
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Old 08-26-12, 08:57 AM   #5
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A top-of-the-line old school racing bike weighed about 20 pounds. Using the absolute lightest components might get you down to 19 pounds.
Modern middle quality road bikes weigh 18 pounds without even trying, and if you can afford it, you can get a bike below 15 pounds. They also have more gearing options and integrated shifting, so no more reaching to the downtube to shift.
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Old 08-26-12, 10:48 AM   #6
chrisreed
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Thanks for the fun and factual answers. My takeaway is that..
* Frames are now aluminum not steel.
* Aluminum is a lot lighter so the fatter frames don't add weight.
* Aluminum lacks stiffness so straight front forks and fatter frames are necessary.
* The 'trail' or 'offset' created by the old forward bend in front forks is somehow (??) created without the bend now.
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Old 08-26-12, 11:24 AM   #7
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Quote:
Originally Posted by chrisreed View Post
Thanks for the fun and factual answers. My takeaway is that..
* Frames are now aluminum, carbon fiber, titanium, stainless steel, other fancy steel, bamboo. Regular cro-mo steel is still used in lower end frames.
* Aluminum is a lot lighter so the fatter frames don't add weight, while adding stiffness.
* Aluminum lacks stiffness so straight front forks and fatter frames are necessary. No, straight or curved is irrelevant. It's the "rake" and trail that matter.
* The 'trail' or 'offset' created by the old forward bend in front forks is somehow (??) created without the bend now. Yes, the offset is created by the fork blades coming out of the frame at an angle relative to the steerer/head tube.
See above for simplified answers.
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Last edited by Homebrew01; 08-26-12 at 01:40 PM.
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Old 08-26-12, 05:53 PM   #8
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Got it thanks.
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