|CARBON SEATPOST FREEZE||fredstaple|
Jan 26, 2004 6:50 PM
|I was reading the string below and someone mentioned that carbon seatposts will freeze in the tube and destroy the frame. Is this true? Can it be stopped? If this happens, why do so many people ride them? Should I sell my Easton? I can't afford a new frame. thanks|
Jan 26, 2004 7:13 PM
|If there is enough bare carbon exposed to aluminum and water introduced frequently, it's possible for carbon and aluminum to corrode and "freeze" the post in the frame. Generally, there is a thick enough coating of clear epoxy on the post to prevent this.
An Al post can also freeze in a carbon frame.
There's a debate about the potential detrimental effect of greasing a carbon post to prevent this problem. I've been testing a piece of greased carbon steerer for a couples of months now, and so far, the grease hasn't hurt it.
I'm using a carbon post in my Al frame with no problems so far, but I don't ride in the rain either. As another example, LOOK sells 25.0mm carbon seatposts that are intended to be used with their Al lugged carbon frames. They must not be too concerned.
|Shouldn't be a problem...||hackmechanic|
Jan 26, 2004 7:25 PM
|Galvanic corrosion happens between two dissimilar METALS. Carbon seat posts will not react with aluminum, steel, or titanium. In fact, on many high end titanium frames carbon inserts are used to negate the need for grease or antiseize when using a seatpost. The only reason to grease a seatpost is to prevent the electric current between the metals so there is no reason for greasing a carbon post when inserting it into a frame either.|
|Shouldn't be a problem...||lyleseven|
Jan 26, 2004 8:49 PM
|I had a carbon post seize in a steel frame. It was a disaster to get it out. I didn't ruin the frame, and was finally removed successfully by the third shop that attempted its removal. I was told that they have encountered this problem frequently with both lubed and non-lubed cf seatposts..FWIW...|
Jan 26, 2004 9:05 PM
|Carbon can be part of a galvanic reaction with a metal. Galvanic corrosion was the reason for the failure of some early carbon frames with Al lugs. Recently read of a severely corroded aluminum seatpost with an aluminum shim, used in a Colnago C-40.
By the way, which Ti frame uses this carbon insert? I've never heard of this.
|I stand correctly....||hackmechanic|
Jan 26, 2004 10:10 PM
|Or I should say corrected.
In either case the rate of corrosion depends on differences in materials and the rate of corrosion between carbon and ti, say, is much lower than between aluminum and titanium. In either case the clearcoat on a carbon seatpost should act as a more than effective insulating layer between the carbon post and frame(as you said above) Greasing the post increases the amount of force needed in the clamp to hold it in place and the liklihood of failure from overclamping. Sure, you post may not get stuck in the frame but it might snap off at the collar if you're not careful.
Seven uses a carbon insert and at one point suggested this negated the need for grease or antiseize. They may have changed their tune since.
Independent Fabrications uses a plastic insert on their ti frames and no grease or antiseize is needed there.
It should also be noted that Titanium and Carbon are both very close to each other and towards the more noble or cathodic end of the scale and less likely to need barriers as they are not very reactive. Aluminum is towards the other end of the scale being very active or anodic which is probably why all those alloy posts got stuck in early generation ti bikes. Steel resides at the anode end as well, reasonable close to aluminum.
Thanks for enlightening me on carbon and galvanic corrosion. I had been misled to believe it was nonreactive, most likely because of the clearcoats.
Jan 27, 2004 5:26 AM
|...puts a carbon sleeve in the seat tube, as the other poster mentioned. Seven's rationale is that it stops squeaks and negates the use of grease. Seven indicates that you can use a thin layer of grease if you want; the carbon sleeve is wrapped in fiberglass (or something like that) so the grease never actually gets to the carbon.|
|Here is a simple fix||Ian|
Jan 27, 2004 12:37 AM
|Remove and wipe clean your seatpost on occasion. Some people are fanatical about bicycle maintenance. They clean the chain, derailleurs and wipe down the frame every couple of rides. They dry the bike off and drop lubes on parts after rain rides. But they let their seatpost sit in place for two years. Well, no wonder it doesn't move. Think about how much you sweat each ride. The largest percentage of your body is over the seat. Think about how much sweat works its way down your seatpost. It just needs a little maintenance like the rest of your bike.
|Here is a simple fix||fredstaple|
Jan 27, 2004 3:24 AM
|Thanks to all for this great advice. I have a new steel frame. Thanks Ian, I'll just clean it every couple of months and more often in the summer|
Jan 27, 2004 3:46 AM
|Close off the slit in the seat tube just under the seat post clamp by packing it with a bit of grease or by putting a piece of tape over it. When riding on wet roads, that's where lots of water sprays right onto the seatpost-frame interface.|| |