How much seatpost flex is too much

[SirEddy]

I've been using carbon seatposts for around 6 years on my road bikes, and have only broken one so far (Selcof) under my 200 pounds.

However I've just gone to a compact road frame, so have a lot more seatpost showing. I've tried an Easton EC90, and Isaac Carbon post, and thye both flex like crazy. It feels fine, and it takes out some of the bumps, but people riding behind me say it's unnerving to see how much it flexes, and I wonder if I'm asking for trouble, particularly as I like to push the seat way back on the rails, which probably exacerbates the problem.

What do you think? Just how much are these things supposed to flex? I know from my windsurfing background that our carbon masts used to flex like anything, and it wasn't really an issue (although I did break a few ) .

Thanks

[allezkmiec]

I've been using carbon seatposts for around 6 years on my road bikes, and have only broken one so far (Selcof) under my 200 pounds.

However I've just gone to a compact road frame, so have a lot more seatpost showing. I've tried an Easton EC90, and Isaac Carbon post, and thye both flex like crazy. It feels fine, and it takes out some of the bumps, but people riding behind me say it's unnerving to see how much it flexes, and I wonder if I'm asking for trouble, particularly as I like to push the seat way back on the rails, which probably exacerbates the problem.

What do you think? Just how much are these things supposed to flex? I know from my windsurfing background that our carbon masts used to flex like anything, and it wasn't really an issue (although I did break a few ) .

Thanks

I'm no engineer, but I'd say that if your riding buddies notice an unnerving amount of flex, it's probably flexing way too much. For a bigger guy like you (at least by cycling standards) riding a compact frame, I think your safest bet would be with something like the Thomson post. I've had 2 in my life, one for 7 years and the other for 5, and they're both as good as new. They're not flashy, and they're not the lightest thing on the market, but they're light, very strong, and simply one of the best-designed bike parts out there. (Right up there with King headsets!) Plus, Thomson does have the Masterpiece post, which is almost identical aside from a bit of extra machining, and will save you a couple ounces. Hope this helps!

[996vtwin]

I've been using carbon seatposts for around 6 years on my road bikes, and have only broken one so far (Selcof) under my 200 pounds.

However I've just gone to a compact road frame, so have a lot more seatpost showing. I've tried an Easton EC90, and Isaac Carbon post, and thye both flex like crazy. It feels fine, and it takes out some of the bumps, but people riding behind me say it's unnerving to see how much it flexes, and I wonder if I'm asking for trouble, particularly as I like to push the seat way back on the rails, which probably exacerbates the problem.

What do you think? Just how much are these things supposed to flex? I know from my windsurfing background that our carbon masts used to flex like anything, and it wasn't really an issue (although I did break a few ) .

Thanks

I'm no engineer, but I'd say that if your riding buddies notice an unnerving amount of flex, it's probably flexing way too much. For a bigger guy like you (at least by cycling standards) riding a compact frame, I think your safest bet would be with something like the Thomson post. I've had 2 in my life, one for 7 years and the other for 5, and they're both as good as new. They're not flashy, and they're not the lightest thing on the market, but they're light, very strong, and simply one of the best-designed bike parts out there. (Right up there with King headsets!) Plus, Thomson does have the Masterpiece post, which is almost identical aside from a bit of extra machining, and will save you a couple ounces. Hope this helps!

I second that , the adjustability on the Thomson is very good also.

[SirEddy]

I agree with your comments on the Thomson seatposts. I use them on my mtn bikes, and have the X2 stem on both road bikes, but considering I have two pretty expensive carbon posts for this bike already, I was hoping someone would just say that the flex is normal and nothing to worry about Wishful thinking I guess!!

[peterb_bt]

You could also try USE seatposts. Last christmas I bought a Litespeed Mira frameset at a very good price in a size XL. Now I know it's a compact frame, but wow it was small. My LBS built it up and they contacted USE to see if they could custom make a "long" seatpost for me. They came up trumps with an aluminium seatpost in 31.6mm and 480mm length. I can tell you one thing for sure, for it's size it was bl00dy light. I can't remember how much, but I'm fairly sure it was under 200g. Unluckily, the Mira just looked way too small with me on it and was replaced with a Storck. The seatpost is now on my Klein MTB.