Airnimal seat tube - replace with a ti tube?

[ishaw]

My airnimal Joey pimping is almost complete, but something has been bugging me about the seat tube assembly. It has a normal but long seat post (30.2 so not that easy to come by a nicer post to upgrade, especially in the length needed) which slots inside another tube, creating a telescopic style post arrangement.

What's there is quite heavy and limiting in terms of actual seat post choice, so my idea is to replace the bottom tube with something lighter, possibly titanium. Whilst doing this I'd like to adjust the internal diameter to allow a greater choice of long and light seat posts

As titanium is lighter and stronger that the current aluminium tube, does this translate to me being able to say get a thinner tube with an id matching a more standard post size?

As the bike is all black, I'd potentially be looking at getting the tube anodised. I assume this isn't a problem with ti with all the coloured bolts out there?

Any input gratefully received on the idea, what id might be possible for a more standard post size, and even a source of a ti tube. I don't need anything fancy done to the tube aside from cutting the slot out for the qr to work/clamp the actual seat post.

Even if I simply got a ti tube in the same dimensions as the existing one, I think a fair bit of weight would be saved, though I'd be stuck with seat post limitations.

After this, the last puzzle piece will be a nice 24 inch, 507 ETRTO wheelset, but I've not seen much in disc only flavour that isn't huge, heavy and for freeride/Dj so not sure when that will happen.

 

[02gf74]

let me see if I get it. you have an aluminium frame which by default has fairly large diameter tubes. you are proposing to fit a Ti tube into the seat tube so it acts as a shim plus it extends past the seat tube for the seatpost to be fitted, and has a clamp for the seat post.

sounds doable but you would need to ream the seat post so the Ti tube is a snug fit and then pin or glue it in place to stop it moving, at a push you could use the original seat clamp to hold it in place but with a short length of tube inside the Ti tube to prevent the Ti tube being crushed.

re: Ti anodising - colours for the oxide are gold, blue, purple range - not sure about green but black is done differently using dyes -you'd have to google but pretty sure black is not a natural Ti oxide colour..

not sure it would look good - can't you just fit a shim and use a long 27.2 mm or another seat post diameter, it will be a hell of a lot cheaper and proven to work.

PS what length of seatpost are you looking for and what is the target weight?


and for those like me who are not familiar with the arrangement, there indeed are two seat post clamps.

 

[ishaw]

Not quite. In the pic above (thanks for posting) you see a normal seat tube which fits into another tube. Both are adjusted via a qr, allowing the bike to fold and adult the seat post height. It's the bottom tube I'm looking to replace (in the pic above its the black tube the seat post is inserted into) for weight saving and hopefully allow a greater choice of seat posts. No reaming, pinning or any other engineering is required.

 

[02gf74]

Yeah, i shouldve googled as i thought you had a small mtb frame.

Ti extension tube should be fine providing it has same od as the bikes seat tube id. You need to ensure wall is thick enough to work as an extension, remember most seat tubes are supported by the stays and top tube.

 

[danson67]

a nice 24 inch, 507 ETRTO wheelset

Have a look at the 24" BMX race cruiser market for rims...Answer do a 24mm wide rim in 28 holes, 440g, though:

https://www.danscomp.com/products-PARTS ... r_Rim.html
Or a Sun Envy Lite, 415g, but 36h only:

Here: http://www.profileeurope.co.uk/product/ ... r-rim/431/

Either could be paired with a super-duper set of MTB race hubs to make a smart set of wheels.
Tyres down to around 26mm wide, too.

All the best,

 

[Rampage]

Did you email me about this?
I think the titanium tube would be too flexy, stick with aluminium.
Green anodising is possible but tricky. I've paid £250 for around 2 meters of titanium tube, silly expensive.

 

[ishaw]

Ti extension tube should be fine providing it has same od as the bikes seat tube id. You need to ensure wall is thick enough to work as an extension, remember most seat tubes are supported by the stays and top tube.

Thanks. This is where my knowledge is limited. I can measure up the OD, but it is the strength/thickness of the tube that I am in no way qualified to decide on, or if I can even get away with what I would like to.

 

[ishaw]

Did you email me about this?
I think the titanium tube would be too flexy, stick with aluminium.
Green anodising is possible but tricky. I've paid £250 for around 2 meters of titanium tube, silly expensive.

Not me, but if you have any thoughts on this and whether I can do it, I'm all ears. My main aim is to open up a world of better seat posts. If in the process I can get a lighter bike out of it, I won't complain.

 

[ishaw]

a nice 24 inch, 507 ETRTO wheelset

Have a look at the 24" BMX race cruiser market for rims...Answer do a 24mm wide rim in 28 holes, 440g, though:

https://www.danscomp.com/products-PARTS ... r_Rim.html
Or a Sun Envy Lite, 415g, but 36h only:

Here: http://www.profileeurope.co.uk/product/ ... r-rim/431/

Either could be paired with a super-duper set of MTB race hubs to make a smart set of wheels.
Tyres down to around 26mm wide, too.

All the best,

Cheers. Ideally after 32H as I have a couple of hub sets already (hope or XT), but I had not come across these in what has been so far a vain search. I hear stans to a 2 inch rim now?

 

[Rampage]

Re:

What's the wall thickness of the current extension?
It's unlikely to be worth it!
Unlikely to be lighter either.