carbon seatpost clamp ..How tight is OK?
07-20-12, 10:11 AM
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carbon seatpost clamp ..How tight is OK?
OK, so I need to adjust my seat post carbon frame carbon post it is not tight and the seat dropped a tad......
A. do I need to get that special paste for seat posts
B. how tight is OK be for damage the dam thing.
am I screwed??? I can just go to the shop but i fear being a SUPERTool asking them to tighten a bolt.
any ideas?
A. do I need to get that special paste for seat posts
B. how tight is OK be for damage the dam thing.
am I screwed??? I can just go to the shop but i fear being a SUPERTool asking them to tighten a bolt.
any ideas?
07-20-12, 10:18 AM
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Some carbon assembly paste is good, but what's the max torque spec on your seatpost? (Mine says max 4.5 Nm, for the record, and I use a 5 Nm torque wrench.)
07-20-12, 10:23 AM
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+1
1. Paste for sure.
2. Torque wrench. The clamp may have the proper torque printed/engraved/cast/machined on it near the bolt.
Basically you want it as loose as possible without allowing the seatpost to move. The paste is like traction goop, it really firms up the connection.
I'd say:
1. Go to your shop. Buy a tube of the paste.
2. Either buy a Ritchey or similar pre-set torque key. It clicks automatically when you're at whatever torque the key is set for. If your clamp requires some other torque then you should buy the torque wrench set.
3. If you ask the shop to tighten your clamp, definitely buy the paste from them. Just like you don't want to eff up your carbon frame, they need to sell stuff to stay in business so you can walk in and ask them for a favor so you don't eff up your frame. The only time a person can be a "SUPERTool" in a shop is if they ask for something for free/favor and don't buy anything in return.
1. Paste for sure.
2. Torque wrench. The clamp may have the proper torque printed/engraved/cast/machined on it near the bolt.
Basically you want it as loose as possible without allowing the seatpost to move. The paste is like traction goop, it really firms up the connection.
I'd say:
1. Go to your shop. Buy a tube of the paste.
2. Either buy a Ritchey or similar pre-set torque key. It clicks automatically when you're at whatever torque the key is set for. If your clamp requires some other torque then you should buy the torque wrench set.
3. If you ask the shop to tighten your clamp, definitely buy the paste from them. Just like you don't want to eff up your carbon frame, they need to sell stuff to stay in business so you can walk in and ask them for a favor so you don't eff up your frame. The only time a person can be a "SUPERTool" in a shop is if they ask for something for free/favor and don't buy anything in return.
07-20-12, 10:32 AM
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if you're worried about it, go buy the paste and wrench in store and ask the mech to show you how to do it once. tip appropriately if so inclined.
i'd say that's a fair exchange.
i'd say that's a fair exchange.
07-20-12, 12:08 PM
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+1000 carbon assembly paste and using only enough torque that it doesn't slip under use.
It seems like there's often stories of people cracking parts even when using a torque wrench at the marked recommendations. Those are usually max torque recommendations, I think, so I prefer enough torque to work under expected loads/usage.
It seems like there's often stories of people cracking parts even when using a torque wrench at the marked recommendations. Those are usually max torque recommendations, I think, so I prefer enough torque to work under expected loads/usage.
07-20-12, 12:21 PM
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+1 for buying the carbon assembly paste and a pre-set torque wrench at an LBS. You ask them to show you the correct procedure with the wrench, they will help you out and you didn't act like a tool, as said, you both win and you know how to correctly tighten the seat post.
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Semper Fi, USMC, 1975-1977
I Can Do All Things Through Him, Who Gives Me Strength. Philippians 4:13
07-20-12, 12:44 PM
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I used to do that. I almost got hit by a car that made an erratic move, and turned with everything I had ... I tried to sort of pull the bike out of the way under me and 'jumped' toward safety. The car missed, but I had sort of twisted at the hips to pull the bike with me. And my saddle was rotated about 30 degrees. Of course, I didn't have my multi-tool with me, and needed to ride like that to the nearest shop and borrow one. Since then, I use a torque wrench.
07-20-12, 01:39 PM
#14
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I'm going to assume the seatpost is the traditional round style, not the seatmast styles coming into vogue.
The answer is: 1) yes, you should use carbon assembly paste, 2) just tight enough so it won't slip. If the seatpost slides all the way down under just the weight of the saddle when you loosen the fixing bolt, you should probably think about a shim. Soda cans make for good shim material. The seatpost should fit tight enough that it requires some force, not a huge amount, but a little, from your hands to move when the fixing bolt is loose, otherwise, when you tighten the clamp, you have the top of the seat tube pinching the seatpost and causing a stress riser, which can lead to the seatpost breaking.
Those recommending torques, ask yourself this: how does the seat clamp know how much pressure a seatpost can take? How does it even know what type of seatpost (aluminum or carbon) is installed? Any max torque recommendations found on a seatpost clamp are strictly to avoid stripping threads.
The answer is: 1) yes, you should use carbon assembly paste, 2) just tight enough so it won't slip. If the seatpost slides all the way down under just the weight of the saddle when you loosen the fixing bolt, you should probably think about a shim. Soda cans make for good shim material. The seatpost should fit tight enough that it requires some force, not a huge amount, but a little, from your hands to move when the fixing bolt is loose, otherwise, when you tighten the clamp, you have the top of the seat tube pinching the seatpost and causing a stress riser, which can lead to the seatpost breaking.
Those recommending torques, ask yourself this: how does the seat clamp know how much pressure a seatpost can take? How does it even know what type of seatpost (aluminum or carbon) is installed? Any max torque recommendations found on a seatpost clamp are strictly to avoid stripping threads.
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"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
07-20-12, 04:29 PM
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I'm going to assume the seatpost is the traditional round style, not the seatmast styles coming into vogue.
The answer is: 1) yes, you should use carbon assembly paste, 2) just tight enough so it won't slip. If the seatpost slides all the way down under just the weight of the saddle when you loosen the fixing bolt, you should probably think about a shim. Soda cans make for good shim material. The seatpost should fit tight enough that it requires some force, not a huge amount, but a little, from your hands to move when the fixing bolt is loose, otherwise, when you tighten the clamp, you have the top of the seat tube pinching the seatpost and causing a stress riser, which can lead to the seatpost breaking.
Those recommending torques, ask yourself this: how does the seat clamp know how much pressure a seatpost can take? How does it even know what type of seatpost (aluminum or carbon) is installed? Any max torque recommendations found on a seatpost clamp are strictly to avoid stripping threads.
The answer is: 1) yes, you should use carbon assembly paste, 2) just tight enough so it won't slip. If the seatpost slides all the way down under just the weight of the saddle when you loosen the fixing bolt, you should probably think about a shim. Soda cans make for good shim material. The seatpost should fit tight enough that it requires some force, not a huge amount, but a little, from your hands to move when the fixing bolt is loose, otherwise, when you tighten the clamp, you have the top of the seat tube pinching the seatpost and causing a stress riser, which can lead to the seatpost breaking.
Those recommending torques, ask yourself this: how does the seat clamp know how much pressure a seatpost can take? How does it even know what type of seatpost (aluminum or carbon) is installed? Any max torque recommendations found on a seatpost clamp are strictly to avoid stripping threads.
More importantly though, I have a 2007 carbon Lemond frame marketed by Trek. I broke a seatpost clamp from overtightening the bolt without a torque wrench (Thank God for the clamp design, as the clamp gave way before cracking the frame), called Trek for a new clamp, talked to an engineer there, and he advised that was the rationale behind that clamp design, i.e. clamp breaking before frame cracking. So, it is not true that any/every max torque rec is to avoid thread-stripping.
07-20-12, 06:52 PM
#16
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Everything you wrote is reasonable except the one highlighted. I remember Thomson specifically warning in their seatpost brochure to make sure that the seatpost clamp does not touch the seatpost, otherwise the stress riser you mentioned can result.
More importantly though, I have a 2007 carbon Lemond frame marketed by Trek. I broke a seatpost clamp from overtightening the bolt without a torque wrench (Thank God for the clamp design, as the clamp gave way before cracking the frame), called Trek for a new clamp, talked to an engineer there, and he advised that was the rationale behind that clamp design, i.e. clamp breaking before frame cracking. So, it is not true that any/every max torque rec is to avoid thread-stripping.
More importantly though, I have a 2007 carbon Lemond frame marketed by Trek. I broke a seatpost clamp from overtightening the bolt without a torque wrench (Thank God for the clamp design, as the clamp gave way before cracking the frame), called Trek for a new clamp, talked to an engineer there, and he advised that was the rationale behind that clamp design, i.e. clamp breaking before frame cracking. So, it is not true that any/every max torque rec is to avoid thread-stripping.
The bit about the seat clamp not touching the seatpost is just standard practice and has nothing to do with the discussion about tightening. The clamp should never touch the seatpost. Ever.
A carbon frame around an aluminum seatpost will never be cracked due to merely overtightening the seatpost clamp. Same way you won't be able to crush a cardboard tube if you filled the inside with cement. Think about it. But again, we are talking about seatposts, not frames. Also, nothing you said contradicted my point that any torque specification printed on a clamp is a torque specification for the clamp, not the seatpost.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
07-20-12, 09:50 PM
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Yes, and in all your examples, the torque recommendation was for the clamp, not the seatpost. You used an aluminum Thomson and the clamp broke. No surprise. Now what if your seatpost had been carbon fiber? Would your clamp know you changed posts and rewrite the max torque spec?
The bit about the seat clamp not touching the seatpost is just standard practice and has nothing to do with the discussion about tightening. The clamp should never touch the seatpost. Ever.
A carbon frame around an aluminum seatpost will never be cracked due to merely overtightening the seatpost clamp. Same way you won't be able to crush a cardboard tube if you filled the inside with cement. Think about it. But again, we are talking about seatposts, not frames. Also, nothing you said contradicted my point that any torque specification printed on a clamp is a torque specification for the clamp, not the seatpost.
The bit about the seat clamp not touching the seatpost is just standard practice and has nothing to do with the discussion about tightening. The clamp should never touch the seatpost. Ever.
A carbon frame around an aluminum seatpost will never be cracked due to merely overtightening the seatpost clamp. Same way you won't be able to crush a cardboard tube if you filled the inside with cement. Think about it. But again, we are talking about seatposts, not frames. Also, nothing you said contradicted my point that any torque specification printed on a clamp is a torque specification for the clamp, not the seatpost.
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