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Old 03-11-17, 08:26 AM   #1
vintagerando 
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New to carbon, frame & seatpost questions

I bought my first carbon framed ride. I am 220 lbs. I have two questions. Keep in mind this is my first carbon bike, giant defy pro. One: I noticed the frame, in the area of the seat stays actually flexes considerably under just the pressure of my hand while off the bike. This is normal right? Second: how high is too high with the seatpost.? I have tried reading about this on the web. Lots of confusing different opinions. I have the seatpost at 60mm. I can really feel the flex when I ride the bike. So do I have the seat too high for a safe ride?
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Old 03-11-17, 05:21 PM   #2
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nothing, huh
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Old 03-11-17, 05:55 PM   #3
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nothing, huh
A few hours is not a sign that no one will answer...

Carbon frames are actually designed to flex up and down to absorb the bumps; that is deemed compliance. If they did not, the ride would be brutal. They are also designed not to flex right to left.

The seat post should have a line on it denoting the minimum insertion point. If it is not inserted at least that far in, it will be really dangerous.

If you do not have the right tools (torque wrench), or products (fiber grip), etc. you should not adjust your own bike or you risk damaging it.
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Old 03-11-17, 08:21 PM   #4
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60mm is nothing, maybe if you go beyond 320mm than we're talking

if you need to raise the seat to get the bike to fit you than raise the seat. There is a line on the post if you go too high. If you want more security, they have 400mm long post, mostly alum. Thomson seat post weight as much as carbon ones and it strong.

and as mention, use carbon paste plus tq wrench in in/pounds or Nm
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Old 03-12-17, 01:08 PM   #5
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A few hours is not a sign that no one will answer...

Carbon frames are actually designed to flex up and down to absorb the bumps; that is deemed compliance. If they did not, the ride would be brutal. They are also designed not to flex right to left.

The seat post should have a line on it denoting the minimum insertion point. If it is not inserted at least that far in, it will be really dangerous.

If you do not have the right tools (torque wrench), or products (fiber grip), etc. you should not adjust your own bike or you risk damaging it.
Thanks. I just ordered a torque wrench on ebay.
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Old 03-20-17, 11:28 PM   #6
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I'm no expert, but I too have a carbon hybrid bike.
My carbon seatpost, nor my carbon handlebars flex. At least not in a way that I've noticed. I'm ~230-240 lbs.
I suppose if your seat is all the way at the highest position, you may have needed a bigger bike frame. When I bought my first Trek the LBS sold me a model too small and I made them swap for a bigger one after a week.
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Old 03-20-17, 11:30 PM   #7
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I'm rereading, and your post is 2.4 inches high? That's not very high.
Are you sure it's the post and not the saddle?
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Old 03-20-17, 11:45 PM   #8
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I just double checked my bike. My seat post isn't flexing, but the rails on my brooks saddle sure is.
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Old 03-21-17, 06:12 AM   #9
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The basic question is, "Do carbon fiber frames and components visibly flex?" The answer is Yes, they do.

I don't ride CF frames, but I have observed CF flex in forks, seatposts, and cranks. The amount and type of flex the OP describes in their chainstay sounds very unusual to me and would be a point of serious concern if the bike were not purchased new from a LBS.

Regarding the seat post, as has been said, mind the minimum insertion mark and it should be fine, some ultralight boutique posts aside, like MCFK, which do have max rider limits, though those are usually at 100kg/220lbs. I wouldn't worry on that count, but if you're concerned, a quick web lookup should satisfy.
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Old 03-21-17, 10:00 PM   #10
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What I hadn't considered was the seatpost length below the minimum insertion mark. So, I am at 60mm mark, but there is another 50mm below the minimum. So, the total inserted is at least 110mm or over 4 inches. What I did not understand is at that the 60mm position is FROM the minimum insertion, NOT to the butt end of the seatpost.
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Old 03-21-17, 11:32 PM   #11
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???
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Old 06-01-17, 03:25 AM   #12
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how high is too high with the seatpost.? I have tried reading about this on the web. Lots of confusing different opinions. I have the seatpost at 60mm. I can really feel the flex when I ride the bike. So do I have the seat too high for a safe ride?
Too high is when the minimum insertion mark is above the seat clamp/tube
Since you have your seatpost inserted until the 60mm mark (that is above your min insert. mark) you are totally fine.
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Old 06-01-17, 06:56 PM   #13
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OK, serious question - that's a compact frame and you only have 60mm of seat post showing above the frame? I mean, this is a marketing picture and probably the way most people ride their bike - there's a ton of seat post showing.

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