Carbon seatpost - replace if scratched??

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08-01-2008, 09:27 PM
Flur

Carbon seatpost - replace if scratched??

So I took my bike in the shop I bought it at for a fit reassessment b/c I was still having trouble with my knees (since I got clipless pedals). I explained that my original fit was dead on but I was concerned that my seat height may need adjustment with the new pedals and being a noob I wanted a professional opinion. The guy that evaluated me clearly felt that my seat was in the right spot, but wanted to help me with my knees so he raised the seat slightly to see if it would improve things. It didn't, and it felt too high, like I was reaching for the pedals, so I lowered it, but I lowered it too low and then spent the rest of my ride readjusting it. At one point I didn't have the clamp loose enough and I scratched the post enough to take the finish off. I read on here that surface scratches on carbon can be fixed with clear nail polish (as long as they are truly surface scratches), so I did that and it looked good as new. I readjusted it to the right height and hand tightened the clamp as hard as I could (I figured as a not-so-strong girl using a micro tool, there was no way I could over-tighten on my own).

Today I went out for my first long ride since I did all the seat adjustments. I now have a bit of low back pain on the right side, and I thought it was b/c the seat was still a hair too high, but when I went to adjust it I noticed that the clamp was loose, and the seat was a full centimeter lower than I had set it! It seems that I wasn't strong enough to tighten my seat clamp to the proper tension :( So the post is now really, really scratched - the finish is removed from about one centimeter of the post on the left side and back. I again used the clear nail polish, but you can definitely see where the scratch is. So my question is - do I need to replace it b/c the integrity may be compromised? Or it that just being alarmist?
08-02-2008, 04:03 AM
Mr. Bloom

Flur,

I have a bike with a carbon post and when I recently took it out for a good cleaning, it had tons of "abrasion scratches" from inside the seat tube. No one seemed concerned...even though it looked like someone had taken sandpaper to it (which is essentially what the friction inside the tube does) it was a large scale version of what you've described.

I'd go ahead and take it for a second opinion at the LBS, but based on my recent experience, my guess is that it's damage from other sources that need to concern you...

It doesn't take brute strength to tighten this thing, so get this checked out as well...the screw might be stripped.

Good luck!

Edited to add:
- check the post to see if it flexes under tension...probably sign of a problem
- take a coin and tap near the scratch and where there's nothing. If you hear a "dead tone", that's a red flag.
I suspect you're OK.
08-02-2008, 05:14 AM
sundial

I think with a carbon fiber bike a torque wrench is in order.
08-02-2008, 05:18 AM
Tuckervill

That seatpost is going to get scratched up from moving it around. Bike makers can't expect them not to, so I'm sure they take that into consideration. Aluminum seat posts get scratched up, too.

I had the same problem with tightening the clamp on my mountain bike. It had a quick release. I think I'd have it tight, but my weight would make it slip down. So, I had to resort to getting it tight as I could and then using my foot to close the quick release. My husband, however, could easily close it with his hand, so I know I wasn't tightening it too much. I'm just weak, is all.

If I had a carbon seat post, I'd be afraid to let him tighten it down--the big oaf doesn't know his own strength. But I'd crank on it as much as I could to get it tight enough to keep from slipping.

I've also heard that some people put electrical tape around them to keep them from slipping, too.

Karen
08-02-2008, 08:05 AM
KnottedYet

I felt so bad for the TdF rider whose carbon seatpost snapped in Paris. The cameras showed him for several seconds, and I sighed with relief when he kind of "sat" on his top tube. (all I could think was "ouch! get off that bike!"):eek:
08-02-2008, 09:02 AM
Flur

Last night after I readjusted the seatpost to the right height I tightened it down as much as I could. I then had my husband tighten it, and he put another 1/2 turn on it. When I got up this morning I checked it and I was able to put another 1/4 turn on it! That's not supposed to happen!

So I rode down to my LBS and they said I had nothing to worry about with the seatpost, but they replaced the bolt in the collar and tightened it to the correct tension. So I'm good to go now :)
08-02-2008, 09:05 AM
Flur

Quote:

Originally Posted by KnottedYet

I felt so bad for the TdF rider whose carbon seatpost snapped in Paris. The cameras showed him for several seconds, and I sighed with relief when he kind of "sat" on his top tube. (all I could think was "ouch! get off that bike!"):eek:

I saw that too. That's what made me worried I about my seatpost scratches! I don't come out of my seat much when I ride, so if mine snapped I'd surely wind up falling onto the back wheel, or worse.:eek::eek: