Author Topic: Going telescopic.  (Read 255 times)

Going telescopic.
« on: September 01, 2018, 05:30:23 pm »
A little while my fixed wheel "urban warrior" was stolen from the bike racks at my local station and I decided that on the rare occasions I take the train it would be better to take the bike with me, with limited bike space availability a folder would seem to be the answer.  The insurance money wouldn't have paid half of a Brommie and anyway I wouldnt use it enough to justify such an expensive machine. 
At the other end of the scale is Decathlon's B'Twin Tilt 100 for all of £139 !    I did see somewhere that it was limited in suitability for tall chaps, but I figured I could live with a lower saddle for short trips.  For the money it is great, but the inability to get saddle high enough was a bit of downer.  It takes a 31.6mm seatpost and somehow they don't seem to make them at the 550mm or 600 mm length I need.

Also to keep costs down it uses an old fashioned saddle clam arrangement:

The seatpost is a welded steel tube with a seam quite evident on the inside which would create difficulties for sliding anything up inside it.  I did try a 28.6mm post I had (as that was what the caliper measure suggested) but it wasn't even getting started.   I briefly thought of getting a cheap 28.2mm post and attempting to file the seam over a sufficient depth - but decided I would never get deep enough to telescope the inner section down.

Browsing for something else I came across this for £3!
designed to shim a 28.6 seat tube for a 27.2mm seatpost (of which I have several amongst many other sizes)
The full length slot would take care of the weld seam - but in fact it was just a little too big in diameter and slightly compressed when fitted.
Tried a 27.0 mm - too big to fit in the shim,  and a 26.6mm - too small and wobbled.  So I lashed out another whole £10 on a 26.8mm !
Perfect fit.

Then it was just a matter of cutting a slot in the non-tapered "bottom" end of the existing post.

(sorry - lousy pic)

and adding the shim and a spare 31.8 seat clamp

(I did tidy that slot up a bit with a round file later)

and now it's all ready for action:

Complete bike folded with the two clamps visible

At full extension there is now more than enough seatpost height for someone a great deal tall than my 6' 3" and the clamps seemed to hold firm on my check ride, so the next job is to remove the unused tapered section for the what was the top end of the seatpost.