Modifying seat tube

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Modifying seat tube
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Posted: Jun 5, 2020 at 15:49 Quote
So just please correct me if I'm wrong, I'm not at all knowledgeable on metal working and that, is it possible to widen the seat tube diameter, as I have a 30mm seat tube and that basically means I can't get dropper post that will fit me as all of them are baso 30.9 and the only ones smaller don't have enough travel
The bike is a norco Sasquatch 2006 btw

Posted: Jun 5, 2020 at 17:25 Quote
You would just need a shim. You can get a 27.2 dropper and a Shim to make this work.

https://www.modernbike.com/cane-creek-seatpost-shim-27.2-to-30.0mm

And no, you cannot widen your seat tube.

Posted: Jun 5, 2020 at 18:12 Quote
While not the tools intended purpose and possibly horrible advise .... depending on the frame material and wall thickness you could ream out a 30mm tube to 30.9.

Its been successfully done before... I am not advising it, just tossing around marginal ideas.

Posted: Jun 5, 2020 at 19:27 Quote
You can open up the seat tube with a device called a Flex-Hone. I'm not super familiar with your frame, but Googling indicates that it's made of fairly thick-walled aluminum. So, you should be able to shave the 0.45mm out of the seat tube without risking damage. I would bring it to a local frame builder or trusted bike mechanic to verify this though.

The Flex-Hone is a great tool, and is pretty quick and easy to use if know what you are doing. I strongly recommend against trying it yourself on your own bike, though. It's really easy to ream it off center, or to take too much material off, or to leave too much cut aluminum in the seat tube - leading to corrosion problems down the road.

The previously mentioned frame builder or trusted bike mechanic will likely have a Flex-Hone already, and if not, you can purchase one for ~35 GBP.

In the off chance that your bike experts agree that it's safe to open up your seat tube a bit, but don't have experience doing it themselves, then you'll want to approach your local auto mechanic. Flex-Hones are used regularly in engine repair and rebuilding. You may need to buy one small enough for your seat tube, as they tend to work with larger bores, but if you are polite and lucky enough, they may do the work for free if you let them keep the tool.

Good luck!

Posted: Jun 5, 2020 at 20:04 Quote
Using a flex hone on your frame will wreck it trying to take this much material off. Sorry guys but this is terrible advice. Proper reaming tools exist and never use a flex hone for more than de--burring or removing paint from a seat tube. Thats too much material anyways to remove.

Posted: Jun 5, 2020 at 21:31 Quote
lance-h wrote:
Using a flex hone on your frame will wreck it trying to take this much material off. Sorry guys but this is terrible advice. Proper reaming tools exist and never use a flex hone for more than de--burring or removing paint from a seat tube.

100%. I don't think its going to wreck your frame any more than reaming in this case but a cylinder hone will take eons to remove this much material with. These tools are for cross hatching cylinder walls and no other purpose, they are not designed to be some sort of handy tube sander. ETA: read wrong, flex hone is still the wrong tool. This is a fools errand any way you play it.

Easy solution: you need a 27.2 dropper post and the appropriate 30mm shim

Posted: Jun 5, 2020 at 21:51 Quote
If you really want to ream your seat tube, which I do not recommend, the proper tool is an adjustable reamer. Take a light pass, adjust, measure often with a set of calipers, and use plenty of cutting fluid. Also don't do it and by a 27.2 dropper and a shim, both exist.

Posted: Jun 5, 2020 at 23:54 Quote
Is there a shim that's easily available to buy (UK) fitting 27.2 in a 30mm seat tube or is there some sort of diy method I could use
I've heard of people using coke cans or aluminium before

Posted: Jun 6, 2020 at 5:02 Quote
Thanks so much
The longest travel droppers I've managed to find is 100mm, do you think that's enough travel?

Posted: Jun 6, 2020 at 7:20 Quote
It depends on the seat tube height of your bike and how high you want it when you are pedaling. It also depends on how much insertion depth is available (you might not be able to fit the whole post in)

For a 27.2 post, I don’t think you will be able to get that much drop, but i did find a 125 mm post

https://www.jensonusa.com/CrankBrothers-Highline-3-Dropper-Post

Posted: Jun 6, 2020 at 9:37 Quote
If you don't mind drilling a hole in your seat tube to accomodate an internally routed dropper post then finding a Crank Brothers post like the one above would be worthwhile. If you don't fancy drilling the frame then you'll need to stick with externally routed posts....

105mm Brand X

https://www.ebay.co.uk/itm/Brand-X-Ascend-II-Dropper-Seatpost-External-27-2-x105mm-Sale-Price-rrp-139-99/283902605209?hash=item4219e9f799:g:k8sAAOSwewpewERL


110mm Tranz X

https://www.bike-discount.de/en/buy/tranzx-jd-ysp36-external-27.2-x-395mm-dropper-post-760697

Also, KS used to offer a 120mm dropper post in 27.2 size if you can find one....

https://www.mbr.co.uk/news/ks-lev-27-2-377303

Posted: Jun 6, 2020 at 19:11 Quote
I'm starting to have a hard time believing that most of you know how to ride a bicycle, let alone fix one or build one. Talk to 10 frame builders - REAL frame builders, who've made more than 50 frames, not hobbyist dilettantes - and if nine of them don't use a Flex-Hone to finish their seat tubes I'll be amazed.

I'm not recommending it as a DIY solution. It's an inexpensive and easy to use tool, but it's very easy to use wrong.

...but it's the ideal tool for cleaning up and deburring bicycle seat tubes, and in the odd case, opening the diameter a little bit.

If you don't think that an experienced tech can remove less than half a millimeter in wall thickness from the seat tube of a thick-walled, 'Shore Hardtail with a Flex-Hone without causing damage, then I don't know what to say except that you are a dumb-dumb poopy-head.

Posted: Jun 6, 2020 at 19:23 Quote
For record. I have been in support of marginal ideas since the beginning.

Posted: Jun 6, 2020 at 20:54 Quote
cmcrawfo wrote:
For record. I have been in support of marginal ideas since the beginning.


This guy... lol

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