seat post slippage

Mine too!!!!  It started in my last Oly.  I've got pieced of coke cans stuffed in there (though I didn't need to expand the post for the clamp) I tighten it to bike-shaking proportions, and nothing helps.  The worst is 50 miles into a long ride, your laboring/struggling and realizes your legs are bunched like your riding a big wheel....

Curious...are you on MTBs, or something with an easy adjust seat post?

I ask because this used to happen to me on my MTB all of the time.  There was a screw on the clamp that I had to tighten down periodically.  It could be the same one you mean though. 

Edited by CindyK 2004-09-08 1:02 PM

I got my first road bike about 4 weeks before my first race. I got everything set up the way I wanted and trained the hell out of those 4 weeks preceding the race. Took the bike into the LBS 2-4x for slippage adjustments and then came race day. Leading up to the race I was riding around 18.5 mph. On race day I had a 17.8 (as I recall) avg speed. Couldn't figure out for the life of me why my time had dropped so much. As I looked at some of the race pictures, the "riding a big wheel" that you called it was what I was seeing in my pictures. I found my seat post had gradually slipped over 4 weeks by about 3-4 inches. I'm determined not to have the same mistake for my next race next week!!!

Things I've done to reduce slipping are tightening the screw "slowly" until I feel a little slight pop. The user manual for my bike gives a max torque for that screw but since I don't have the proper tools, the pop feel seems to be working and the seat post doesn’t look damaged. Also, get used to checking the middle of the crank set to the top of the post measurement. My seat post is black but I found I could mark it with a sharpie and still make out the mark...made it much easier to see if it had slipped.

Other than this I'm looking for more info on this same subject.

Don't know if this applies to seat posts, but it worked for my cantilever brakes that continuously slipped when I made any adjustment or braked hard. I bike guru friend greased the threads on the tightening screws, so that the torque on teh screw works towards pulling components together, instead of just working against friction in the threads. It worked great and my old cantis have stayed in alignment well for the past several rides.

Maybe try greasing teh tightening assembly (not the seat post) ?

If its the screw coming lose, then you can buy some stuff called Thread Lock (I believe it comes in a blue tube and you can probably get it at your LBS or an automotive parts store like NAPA). Its a gooey stuff that will prevent the screw from backing out.

You can also replace the seat post clamp if its stripped. They're relatively cheap.

Edited by Motivated 2004-09-09 11:14 AM