pasopia

I would like to change the seatpost on my swift to a Biologic Zorin postpump from Dahon. This post comes in a 33.9mm diameter. I remember from some old threads people were swapping out their seatposts, but I also remember somebody having a frame crack from doing this. The xootr site says that the stock seatpost diameter is 32.9, but I thought people were getting away with using 34mm seatposts. Any help/advice would be great.

doco

mine is 34mm, I am pretty sure the newer ones are 34mm

jur

34mm, and if you measure them, they are 33.9mm.

I think the frame crack issue is not necessarily elated to non-stock seatposts since at least one case that was reported had the stock post; however please note that the seatpost is a structural member of the frame and is therefore part of the frame structural integrity. The bike cannot be ridden with a short post stuck in the upper portion only - that will lead to the frame cracking.

pasopia

Thanks, that's what I wanted to hear!

pasopia

Hmm, I emailed Peter Reich and he advised against it. He said the swift seatpost is slightly smaller than the dahon seatpost.

itsmoot

Theres no mention whether this is a steel Swift, aluminum Xootr Swift or what vintage the frame in question is so I don't know if these measurements by dial caliper are useful. So for whatever its worth:

Dahon Speed D7 stock seatpost: 1.334" (33.8836 millimeters)

Dahon Telescoping seatpost: 1.337" (33.9598 millimeters)

Xootr Swift stock seatpost: 1.3375" (33.9725 millimeters)

Xootr Swift stock seatpost:


Dahon telescoping seatpost:


Unfortunately the stock seatpost on my Dahon Speed has no markings besides minimum and maximum insertion lines.

I'm not an engineer so the ones here can decide whether a few thousands or ten-thousands of an inch would be critical to seatpost diameter. I've been using the Dahon telescoping post on my Swift now for 600+ miles and 80+ folds/unfolds with no ill effects.

pasopia

Thanks for those numbers. I have an aluminum frame that I bought direct from Peter last year. Yeah the numbers seem to be close enough, but I'm not expert. Has anyone ran into a problem using a seatpost other than stock on a swift.

jur

My call is those 34.0mm seatposts from NL(?) are all identical in manufacture. What you are seeing is manufacturing tolerances. My wife's Yeah also had one of those posts, I saw it was the same in specs as the Swift's, so I started using them interchangably.

In fact, from the Yeah's post I made a seat post adapter to take a 31.6mm post (see last pic in the Swift page in my sig). Later I used a carbon Easton EC70 post instead in the same adapter. Still later, the adapter cracked at the seat post's end. That was due to the lever action of the carbon seat post and not the post's dimensions. So I have temporarily gone back to the original Xootr post. The original post is a bit large, it fits with some difficulty into the lower seat tube.

There has been one case where a Xootr frame failed, and the user was using a non-Swift post, see this thread https://www.bikeforums.net/folding-bikes/286609-making-swift-lighter.html

I doubt that it failed due the seat post, because there has been an identical failure with the standard seat post. And Xootr have made those replacements very quickly and the newer frames are slightly thicker, so I think they acknowledge the earlier version had a slightly risky design problem with the frame strength. My frame is one of the older, thinner-walled ones. I regularly check the spot were the other frames have failed.