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Picked up a Btwin Tilt folding bike to use as a station bike/ shopper/ going for short rides with my kid via car or train. Stock pic.

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A ride across London today revealed a couple of issues from my perspective.

Firstly the stock seatpost is too short. I'm 5'9 with a 30" inside leg and I can't get the seat high enough. I wonder if a Brompton telescopic would fit or could I extend the stock post somehow (fitting a smaller seatpost into the top maybe).

Secondly the handlebars are too high and close. The bike could do with being longer in the top tube and lower at the front. I'd hoped flat bars would sort this a bit but I feel something more drastic is needed.
First thought is to flip the risers so I can move the bars down and forward.

Second idea is to cut the top part of the headtube and re fix the bar clamp into the headtube lower down. Looks like this is a separate part that has been fixed in. There is a rivet in the back. Hard to see in the pic I'll take a better one tomorrow.

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Third idea is to chop the headtube and fix a bit of seatube or a carbon expansion bung into the hole then fit a stubby aheadstem.
I'll need to measure everything first to see if this will work.

I don’t think I’d start by cutting up the head tube tbh. Maybe some bars a bit like these https://www.tredz.co.uk/.Dedacciai-Crononero-Low-Rider-Tri-Bar_48200.htm?sku=126590&utm_source=google&utm_medium=cpc&utm_campaign=Handlebars&gclid=CjwKCAjw5s6WBhA4EiwACGncZarN_p3Qa0dSf6DL40D4cNiuvUCCCpGmnBniOMf7UqiS2-lGBL9FKxoClPcQAvD_BwE could help?
I’ve done the seat post inside a seat post on a stuck post before, if you can get one the right size it’ll be fine.
Good luck, I want to see how this turns out.

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I am quite keen to chop the head tube (appreciate this could be terminal).
The top section appears to be the same diameter and the clamp is a separate piece.

I like the thinking on the bars, however I think they will inhibit the folding capacity. I won't be folding it loads but handy when I do.

Second idea is to cut the top part of the headtube and re fix the bar clamp into the headtube lower down. Looks like this is a separate part that has been fixed in. There is a rivet in the back.

I am absolutely not an expert but this sounds like a terrible idea.

I agree, it's kind of why I'm tempted to do it. Nothing happening until I get some verniers on there to see if anything is (close to ) a stock size that could be bodged.

it's kind of why I'm tempted to do it

Ha ha. Slice the top off and stick a quill stem down it :)

Quick release on the handlebar clamp so you could fold the bullhorns as and when needed?

Folds down quite small, weight weenie v brakes

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No clues about the handlebar clamp from the rear, here's a better pic of the grub screw so I assume this part is bonded?

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The diameter of the tube below the handlebar clamp is uniform for 15cm or so.

What's the seatpost size and length?

I've replaced posts for longer ones in a couple of small bikes. Finding something 50cm+ was a bit of a challenge in certain tube widths

I bought a 31cm long one from Aliexpress for my Dahon Uno.

I’m tempted by a shorter 21cm one as well.

A Brompton flat bar is 924mm off the ground if my googling is correct. This has a larger wheel but the bars are 1100mm high.
Don't have calipers to hand today but eyeing up with a ruler the top part of the headtube looks to be 25.4mm. so a aheadstem should fit over nicely. Might need to consult tester for a safety check.

sure you have seen it before, but just in case:

https://www.pedalroom.com/bike/btwin-tilt-100-39556

also i think dahon use that streering system and they're very popular in the asia, so maybe they make shorter ones. There is lots of stuff on AliExpress.

I love this god damn lunitick idea, if it fails just buy a shorter folding stem. Question is how wide is the tube?

I had a dahon uno for a while which is a similar setup, seatpost on that was just about long enough for me at 181 right on the limit, so maybe a dahon post would fit and be a better length?
I think you can get an adjustable height steerer for dahons that might fit on the btwin as well? have you tried taking the steerer off at the head tube to see how it's attached?
the dahon stem also has a quick release bar mechanism that you can flip open so you could potentially fit BMX bars or something.

tldr, maybe just get a dahon? 😂

found a pic.
it was quite a cool bike actually, coaster brake so no cables to the back and could do wicked skidz.

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