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Just thinking - the steerer tube is not 'unsupported'. It is supported by the spacers. The spacers are supported on the top of bearing, which in turn is supported by the head tube. They would act like a 'flying buttress' transferring the force into the head tube. Even better if the spacer is a single piece. So as long as the spacer is strong enough, and there is no play in the system, you can have a longer steerer.
His version of "supported" is different from yours. He is talking about getting farther away from the top tube/upper headset bearing. Even supported by spacers stacked tightly, you are still increasing your lever by raising the bars high above the headset stack.
 

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His version of "supported" is different from yours. He is talking about getting farther away from the top tube/upper headset bearing. Even supported by spacers stacked tightly, you are still increasing your lever by raising the bars high above the headset stack.
I acknowledge the increase in leverage, but the leverage is not acting in the steerer tube alone. Don't the spacers mechanically form part of the headset stack? They are resting on the headset. It isn't like a quill stem, where the extension of the stem out of the steerer tube is unsupported.

If you take a tube, put it inside two pieces of tube that are clamped together to form a rigid unit, then it is the strength of the outer tube that matters. So long as the combined outer tube can withstand the compression and bending forces, there is little stress in the inner tube, except where it exits the ends of the outer tube. In a bike, the stem, spacers, upper bearing cap, upper bearing, head tube, lower bearing should all combine into a rigid system to support the steerer tube.

So what it comes down to is a longer steerer tube just needs to be supported by an appropriate spacer.

Just out of interest, what is the incidence of steerers breaking above the head tube, vs at the fork crown? And what is difference between adding 1cm to the stem, vs adding 1 cm to the steerer?
 

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look alike bikes

Hi ,can anyone please tell me if there are chinese frames that look exactly like the originals ?
im looking for road,tt, and mtb frames ,but i want them to look 99 % as the originals ,can some one help me this ? thanks a lot .
 

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Ultegra R8000
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I acknowledge the increase in leverage, but the leverage is not acting in the steerer tube alone. Don't the spacers mechanically form part of the headset stack? They are resting on the headset. It isn't like a quill stem, where the extension of the stem out of the steerer tube is unsupported.

If you take a tube, put it inside two pieces of tube that are clamped together to form a rigid unit, then it is the strength of the outer tube that matters. So long as the combined outer tube can withstand the compression and bending forces, there is little stress in the inner tube, except where it exits the ends of the outer tube. In a bike, the stem, spacers, upper bearing cap, upper bearing, head tube, lower bearing should all combine into a rigid system to support the steerer tube.

So what it comes down to is a longer steerer tube just needs to be supported by an appropriate spacer.

Just out of interest, what is the incidence of steerers breaking above the head tube, vs at the fork crown? And what is difference between adding 1cm to the stem, vs adding 1 cm to the steerer?
The difference is how it triangulates with the top tube. Anything above the top tube is considered unsupported, whether its a quill stem or sitting on spacers. The top cap of the stem doesn't offer enough strength to properly squeeze the spacers, to consider them a solid support tube. The leverage at the handlebars is enough to flex the steerer at the stem clamp area. The farther away you get from the top tube, the more leverage you can exert on the steerer.

If you're not an agressive rider, it doesn't matter. If you're muscular or heavier, and like to stand up on climbs. or sprint, then use caution with a big spacer stack.
 

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The difference is how it triangulates with the top tube. Anything above the top tube is considered unsupported, whether its a quill stem or sitting on spacers. The top cap of the stem doesn't offer enough strength to properly squeeze the spacers, to consider them a solid support tube. The leverage at the handlebars is enough to flex the steerer at the stem clamp area. The farther away you get from the top tube, the more leverage you can exert on the steerer.

If you're not an agressive rider, it doesn't matter. If you're muscular or heavier, and like to stand up on climbs. or sprint, then use caution with a big spacer stack.
The top cap isn't what holds it together. Once the stem is clamped, it is the stem that holds it all together, otherwise you wont get the bearing surfaces together. Also, there is a difference between multiple, small spacers (as is usually supplied with bikes) and a single, solid spacer (as is available after-market). Why doesn't the spacer support the steerer tube and transfer the forces down to the head tube?

"The leverage at the handlebars is enough to flex the steerer at the stem clamp area." This true regardless of the length of the steerer, and is a function of the stem length and handlebar reach. Did you mean to say to say 'at the top of the head tube'? And again, what is the difference between 30mm stack+120mm stem against 50mm stack and 90mm stem?
 

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Hey all!

After the small paint fiasco, I finally got on it and finished my first build. Very happy with the bike overall. I think this frame paired up with the Ksyrium SL wheels make up for a very smooth responsive ride. Couldnt be happier.

Frame: FM018 from DengFU size 54
Handlebar: HED Original
Aerobars: Oval alloy single bend extensions
Stem: Nashbar 80mm 7deg. (temporary, pending fit)
Shifters: Dura Ace SLBS79 Double 10spd
Brake/shift cables: Jagwire Racer Kit
Wheels: Ksyrium SL
Tire Front: Continental GP 4 Seasons
Tire Rear: Continental GatorSkin.
Bar tape: Sunlite
Front derrailleur: Shimano Ultegra 6600
Rear derrailleur: Shimano Ultegra 6600
Crankset: Shimano Ultegra 6600 53-39 172.5
Bottom bracket: Shimano Ultegra 6700 Hollowtech II
Chain: Shimano DUra Ace
Rear cassette: Shimano Dura Ace 11-25
Pedals: Shimano Ultegra 6610
Front brake: Tektro 530, white
Rear brake: Tektro 725 side pull, black
Brake pads: Shimano R55C3
Saddle: Profile Design Tri-Stryke
Skewers: XLC Quick Release Skewers
Bike computer: Motorola MotoActv

Total Weight: 19.4 lbs, with pedals and all.


Here are a few pics...





















 

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Thanks pyattbl. :thumbsup:

Im pretty happy with it. Took it for a few rides already and feels like an entire different world compared to my prior tri bike (2009 Felt S32, alluminum and very heavy!)

Looking forward to some longer rides on it as well as some hill action...
 

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Ultegra R8000
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The top cap isn't what holds it together. Once the stem is clamped, it is the stem that holds it all together, otherwise you wont get the bearing surfaces together. Also, there is a difference between multiple, small spacers (as is usually supplied with bikes) and a single, solid spacer (as is available after-market). Why doesn't the spacer support the steerer tube and transfer the forces down to the head tube?

"The leverage at the handlebars is enough to flex the steerer at the stem clamp area." This true regardless of the length of the steerer, and is a function of the stem length and handlebar reach. Did you mean to say to say 'at the top of the head tube'? And again, what is the difference between 30mm stack+120mm stem against 50mm stack and 90mm stem?
No, I really meant to say at the stem clamp area. I'm not sure how else to explain it. The top cap delivers all the clamp force to the spacers. the stem clamp bolts just maintain that clamp force. The steerer flexes where it is clamped, down to where it is rigid. (at the top tube.) It means the stack of spacers is also not rigid, so it's not doing the job of supporting the steerer tube. The more spacers you have between the bottom of the stem, and the top of the top tube, the more it'll flex, since you are increasing the length of lever arm from the handlebars to the top tube.

If, for example, you could have the top tube mounted really low near the downtube, but kept a long headtube, the headtube would also be unsupported, and flexible. The difference in your example is 20mm more of unsupported steerer tube.

And again, its not really an issue, unless you're an agressive rider that puts a lot of force on the handlebars.
 

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I'm thinking of building a bike for my girlfriend. She loves to ride, and has a $20 garage sale bike. She is a social worker (read: poor) so we'd try to keep it cheap. One option is to go to the local fall bike show and get a cheap aluminum bike. The bike show is next week.

Otherwise, we were at the bike store and looking at Specialized aluminum bikes which were close to $1000. I said for a little more we would be able to go with a carbon chinese bike. I can get some lightly used Ultegra for $400 or so, alright wheels for $300, so the idea is to keep the frame as cheap as possible.

Any recommendations on the place to get the least expensive (not cheap) frame / fork combo? I saw e- Hong Fu has the HF-FM001+FO001 for $325. Any other ideas?
 

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I'm thinking of building a bike for my girlfriend. She loves to ride, and has a $20 garage sale bike. She is a social worker (read: poor) so we'd try to keep it cheap. One option is to go to the local fall bike show and get a cheap aluminum bike. The bike show is next week.

Otherwise, we were at the bike store and looking at Specialized aluminum bikes which were close to $1000. I said for a little more we would be able to go with a carbon chinese bike. I can get some lightly used Ultegra for $400 or so, alright wheels for $300, so the idea is to keep the frame as cheap as possible.

Any recommendations on the place to get the least expensive (not cheap) frame / fork combo? I saw e- Hong Fu has the HF-FM001+FO001 for $325. Any other ideas?
Are you in Toronto? The bike show is a good place to start looking for a cheap complete bike. Trek ususally has a booth and they have a huge line so it must be a good deal. Another option is to go to Sportcheck. They currently have some Jamis bikes at 40% off and you can sometimes use a team assist coupon for an extra 10%-20% off.

Building a bike is not that cheap once you get into tools (which you'll use again), extra stuff like pedals, bottle holders, shipping.... it adds up.
 

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I am in Toronto, so we're hopeful for a good deal at the bike show. I have the tools, but you're right its all the small things like cables that add up! But the idea is you pay a little more now but you have a carbon bike that you can ride for a long time without need to upgrade.
 
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