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I tried the Xiaomi qicycle electric folding bike and I really liked it.

The only problem is its size. I already know how to raise the handlebar, but I'm not sure how to raise the seat. It should be just about five centimeters higher, in order to fit with my height. I can't replace the seat tube with a longer one, because it's already the longest I can find. I found this product. Its purpose is not to make the seat bar longer, but it would accomplish this goal anyway. I was wondering whether there are other possibilities besides this.

Rinsten Spring https://cdn7.bigcommerce.com/s-hqha07okb6/images/stencil/1280x1280/products/119/384/Rinsten_Serial_Black__90487.1525094585.jpg?c=2&imbypass=on

https://gloimg.gbtcdn.com/gb/pdm-product-pic/Electronic/2016/08/17/source-img/20160817172730_50719.jpg from linked site in comments

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    Your first link is dead, and there are wide variety of "Xiaomi QiCYCLE" bikes. So we have no idea what kind of bike you're talking about. – Daniel R Hicks May 31 '18 at 22:52
  • @Daniel R Hicks The link works for me. Maybe it's not accessible from your location, I don't know. Anyway, I've updated the question, it's the electric folding bike. – User May 31 '18 at 22:55
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    This one, it.gearbest.com/bikes/pp_434406.html – User May 31 '18 at 22:56
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    WIth a folding bike and travel bikes the height of the seat is often not optimal. They do not have enough seat tube for the seat post to go into to be able to have an extra long seat post safely. I doubt there is much you can do really. They are simply not made for long excursions and designs are focused on being able to fold, not comfort and usability – Nate W May 31 '18 at 23:08
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    Not necessarily no, that doesn't look like it gives a whole lot more height, but seat posts have minimum insertion marks on all bikes because of the leverage applied to the seat tube is all i was implying. Likely that device would be fine but there is likely not a lot beyond that that you could do depending on the seat post and bike design. – Nate W May 31 '18 at 23:23
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Yes that spring thing will add about 25 mm of extra height once you're seated on it.

On the downside it will make your seat wobblier in all directions. They make the saddle feel like its coming loose and about to fall off. Its an unpleasant feeling, though you should get used to it given enough time.

You can get 600mm seat posts, but the difference is probably not worth the cost.

I too have a folding bike that is functionally too small for me. My plan is to get an engineering firm to fab up a new seatpost from tube, and to use an old-school saddle clamp on the end rather than an integrated saddle clamp. This will require a minimum of operations, being necking down the top, and applying knurling to the lowest part.

Second option is to find a seat post in two parts. You might see these on Unicycles where the rider leg length could be a large range. These tend to have two QR clamps and a substantial length of overlap. I've not found a useful sized one yet. These are also built for bikes with little to no sideways pressure, so the bending forces on the post will be increased.

http://funicycle.com/magasin/images/r/spares/seatPost/rallongeFourcheTubeSelleMonocycleicloDebutantGiraffe22.25.4mmFrameExtension_2.jpg

Third option is a bit reversed - if you fit longer cranks to the BB, then your lower foot will be lower again, effectively increasing your seat post length. However this could get expensive and will only gain you 10mm going from 165 to 175mm cranks. Then there is the increased risk of pedal strike on turns.

A cheap option is to find the shoes you own with the thinnest sole, and make them your riding shoes. This will only give a few millimetres thougj

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  • Thank you! But I don't understand the second option. Could you please show me an example of the kind of seat post you are talking about? Even a picture would suffice. – User Jun 1 '18 at 7:36
  • Anyway, the extra added height from the mentioned device is not just 25mm but about 50mm to 70mm, based on the rigidity setting. I've asked the manufacturer. – User Jun 1 '18 at 8:44
  • @user I'm guessing that's an uncompressed height. Put a body's weight on it and it will compress some amount. – Criggie♦ Jun 1 '18 at 10:25
  • Mmh, you're probably right. Thank you for all! – User Jun 1 '18 at 12:23
  • @User if you do buy the part, please come back and let us know how it works for you. SE specifically allows the Original Poster to answer their own question. – Criggie♦ Jun 2 '18 at 0:09
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Seatposts come in many diameters, some as small as 22mm and you can buy shims to allow you to use smaller diameter seatposts in bikes with larger seat posts.

While I'm not exactly sure, it looks like that bike uses a 30.9 seatpost. If so you should be able to insert a smaller diameter seatpost inside it. This would require cleanly cutting the top of the seatpost and that there is no internal butting inside the seatpost. You'd machine a slot and stress relief hole in the top of existing seat tube and use another seat tube clamp.

In effect you would be transforming the existing seatpost into an adjustable seat tube.

I would get the longest small seatpost I could find. Older BMX bikes should be a good source for long and skinny seat tubes. Thomson would be my choice. https://www.bikethomson.com/product/elite-seatpost/

I'm not entirely convinced this is a good idea, but I think if you can get a reasonably long skinny post, it's probably okay as long as you watch where the inner post ends for any cracking/bumps on the outer post.

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  • A thicker-walled tube will help too, at the cost of increased weight. – Criggie♦ Jun 2 '18 at 8:37

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