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How much to tighten seat tube clamp around carbon post?(17 posts)

How much to tighten seat tube clamp around carbon post?fbg111
Aug 28, 2002 9:33 AM
I'm concerned that too much tightness in the seat tube clamp could overstress the end of the carbon fiber seat post and cause it to crack, but have no idea how much to tighten the clamp or how to measure the tightness. Anyone know anything about this?
re: How much to tighten seat tube clamp around carbon post?peloton
Aug 28, 2002 9:38 AM
Check with the manufacturers of your frame and seatpost. I have a Giant TCR with a Time carbon post, and I go to 43 in/lb as reccomended by Giant with no problems. You should be able to find this info from the manufacturers pretty easily. Maybe someone here could help if you posted what frame and post you are talking about.
re: How much to tighten seat tube clamp around carbon post?clintb
Aug 28, 2002 10:06 AM
Peloton,

Where did you get the 43in/lb figure from? I have an '01 TCR Zero, called Giant and they said 120kgf-cm. That works out to 104in/lbs. I thought they were nuts, so I've only been going to around 60in/lbs.
re: How much to tighten seat tube clamp around carbon post?peloton
Aug 28, 2002 5:27 PM
All the '02 Giant TCR's come with a sticker on the seat tube stating that tightening the bolts tighter than 43in/lbs can potentially damage the frame. The 104 figure seems really high to me, but maybe it's different for the '01's. The shop I ride for only picked up Giant this year, so I haven't worked on the brand for long. I haven't had any problems with the 43in/lbs figure for what it's worth.
re: How much to tighten seat tube clamp around carbon post?clintb
Aug 30, 2002 8:00 AM
Ah, yes the '02's have the dual bolt binder system instead of the clamp of years past. Like I said, I've only been going to about 60in/lbs and that works great with the USE carbon and USE shim.

For anyone having creaking problems on their TCR w/stock shim. Get the shim from USE. It's UPVC (plastic) and doesn't creak one bit. The stock shim is 27.2 to 31.6 from what I've measured with a digital micrometer. Oh, either Cambria or Bulltek can get the shim.

http://cambriabike.com/seatposts/seatpost.htm Scroll to the bottom and select the drop down list for 27.2 under "Seat Post Reducer Shims".
120kg-cm alsofbg111
Aug 28, 2002 10:49 AM
I have an '02 TCR 2. I pulled out the seatpost and there's a sticker near the bottom that says 120kg-cm also. So what tool do you use to measure that pressure?
Giant shim problems with carbon.tj90
Aug 28, 2002 11:59 AM
I wanted to ask you guys if you have had problems with the Giant seatpost shims. I have an Easton ec70 carbon seatpost and trashed the last post because the shim collapsed and started cutting into the post. On closer inspection, the thin walls adjacent to the rear reinforcement rib collapsed and the rib on the shim was digging into the post (I made sure the slot was to the front) as indicated on the shim.

The seatpost binderbolt was high to prevent creaking and Lithium greased every other stresspoint to isolate it to the shim/seatpost interface. Im sure the high pressure contributed to the problem with the shim. However, why cant giant make a shim with no slots near the binderbolt? It would distribute the compression between the frame and shim over twice the area with a slight weight penalty.
Giant shim problems with carbon.fbg111
Aug 28, 2002 12:45 PM
Haven't had any problems yet, but have only owned it for a few weeks.
USE recommends tight enough so the post doesn't slip.triple shot espresso
Aug 28, 2002 12:28 PM
That is literally how the directions read. You are supposed to mark your post with tape, tighten it hand tight, then see if it slips, if it slips, reposition it and make it a little tighter. They also direct you to turn the clamp around so that it is pointing backwards and the opening is on the front side.
USE recommends tight enough so the post doesn't slip.fbg111
Aug 28, 2002 12:48 PM
Thanks, that sounds like a good guide. As for the clamp, with the TCR you can't turn it around. It's part of the seat post.
turning the clamp around does nothing butelviento
Aug 28, 2002 12:56 PM
use friction to make it harder to tighten the bolt. It achieves exactly the same result as simply not tightening it as much as you otherwise would. In other words, you can just tighten it less without turning it around.

In still other words, it only helps those guys who will tighten the clamp until they can't turn the allen key any more.

Tighten it until it doesn't slip is a good way to go.
What tool to measure the tightness of the seatpost clamp? nmfbg111
Aug 28, 2002 12:48 PM
What tool to measure the tightness of the seatpost clamp? nmCrankist
Aug 28, 2002 2:37 PM
Basic torque wrench for that range. See your friendly Craftsman (or similar) salesman. You'll probably need a drive adapter for metric allen keys. Don't forget to lube the bolt threads.
Mike
Thanks. nmfbg111
Aug 28, 2002 3:22 PM
What tool to measure the tightness of the seatpost clamp? nmaliensporebomb
Aug 29, 2002 2:46 AM
The bolts holding the post on the cavity? I thought lube was supposed to stay far away from carbon or am I misunderstanding?
re:fbg111
Aug 30, 2002 4:35 AM
I don't know, but when he put my bike together, the dealer greased the inside of the seatpost. There's a little circular rubber/plastic slide that goes into the seat tube first and separates the carbon post from the aluminum tube. Maybe the grease had something to do with that.
re:clintb
Aug 30, 2002 8:05 AM
fbg111,
I believe the small rubber part you're referring to is nothing more than a dust/water shield.

As to questions about grease on a carbon post. You don't need it. Grease is to keep parts from corroding. Oxidation, rust, etc.. Carbon doesn't rust, so no grease necessary.