Titanium seatpost that is all titanium

[mikeymo]

I am finishing last year's bike build. The seatpost was borrowed and needs to go back to its donor (bike). It's a touring bike in Reynolds 853 (at least the seat tube is). 27.2 dia. Looking at how it's set now there is 430mm from the rails to the first bottle carrier bolt. There's about 25mm setback, but I could probably get away with less, as the B17 saddle is getting towards the part of the rails where they flare outwards.

I'd like titanium (or even steel?) because it's the only other material, with steel, that has a fatigue limit. But most titanium posts seem to have aluminium clamps.

Are there any ti posts that have ti clamps?

Does it matter?

And/or what does anybody think of this:

http://freshtripe.co.uk/nitto-s84-lugged-seatpost-27-2mm/ (though probably too much setback for me)

Spa have these, which look OK.

https://www.spacycles.co.uk/m2b0s84p2814/USE-Sumo-Titanium-Seatpost-long

[Brucey]

Moots seat pin is worth a look. Clamps are aluminium but they are a pretty strong design.



FWIW most Ti seat pins are built light, rather than built for infinite life.

cheers

[mikeymo]

Thanks. Moots seem to be difficult to source in the UK. And also very expensive. I'm kind of looking more at USE or Van Nic at the moment.

Or else just a good aluminium, which seems to be Thomson, and replace every so often.

[mikeymo]

Also Brucey, I know you're good at the engineering type stuff. I don't have a lot of seatpost showing, about 120mm, rails to collar. So with some long seatposts I'm nearing the limit due to the bottle cage bolts. But thinking about length:

Posts always have a minimum insertion mark, to reduce the possibility of bending, yes?

In which case is more even better? In other words if I have lots of "spare" length of seatpost inside the seat tube is the whole thing stronger? Or is it as simple as once the post is past the top tube/seat tube junction, it doesn't make any difference. In which case I might as well get a shortish one and save some weight.

I notice the Thomson Mantelpiece has a 'bending fuse' where it promises to bend, not break, at the post clamp. Don't know how often this has happened or been tested. But a neat idea.

[mattsccm]

I have a Chinese one that I think is all Ti. The clamp most certainly is very very tough, so not a cheaply alloy. Bolts were Ti and crap.

[mikeymo]

I have a Chinese one that I think is all Ti. The clamp most certainly is very very tough, so not a cheaply alloy. Bolts were Ti and crap.

Thanks, do you have a name for it or a link?

[mattsccm]

Sorry, no idea. EBay in 2014

[Brucey]

Also Brucey, I know you're good at the engineering type stuff. I don't have a lot of seatpost showing, about 120mm, rails to collar. So with some long seatposts I'm nearing the limit due to the bottle cage bolts. But thinking about length:

Posts always have a minimum insertion mark, to reduce the possibility of bending, yes?

In which case is more even better? In other words if I have lots of "spare" length of seatpost inside the seat tube is the whole thing stronger? Or is it as simple as once the post is past the top tube/seat tube junction, it doesn't make any difference. In which case I might as well get a shortish one and save some weight.

I notice the Thomson Mantelpiece has a 'bending fuse' where it promises to bend, not break, at the post clamp. Don't know how often this has happened or been tested. But a neat idea.

The ideal insertion depth may vary depending on the stiffnesses of the frame and the seat pin, but in general more insertion is better, yes (right until it seizes in the frame and you realise the problem is a lot worse than you thought....). You can always shorten a seat pin but making it longer is much more difficult. If you are to shorten a seat pin there is something to be said for slash-cutting it so that the front is longer than the back; this makes the tip of the seat pin slightly more flexible and makes the stresses less localised where they are transferred into the frame.

Thompson seat pins are light and clever in some ways but even their 'layback' model has no real layback and the aluminium alloy they use is completely unsuitable for UK winter use; it is difficult to find a commonly used aluminium alloy that corrodes more readily. IIRC they also say to throw their aluminium seat pins away after 10000 miles or something. Mechanical fuses are all very well but if the enemy is fatigue they are about as much use as a chocolate teapot.

cheers

[mikeymo]

Also Brucey, I know you're good at the engineering type stuff. I don't have a lot of seatpost showing, about 120mm, rails to collar. So with some long seatposts I'm nearing the limit due to the bottle cage bolts. But thinking about length:

Posts always have a minimum insertion mark, to reduce the possibility of bending, yes?

In which case is more even better? In other words if I have lots of "spare" length of seatpost inside the seat tube is the whole thing stronger? Or is it as simple as once the post is past the top tube/seat tube junction, it doesn't make any difference. In which case I might as well get a shortish one and save some weight.

I notice the Thomson Mantelpiece has a 'bending fuse' where it promises to bend, not break, at the post clamp. Don't know how often this has happened or been tested. But a neat idea.

The ideal insertion depth may vary depending on the stiffnesses of the frame and the seat pin, but in general more insertion is better, yes (right until it seizes in the frame and you realise the problem is a lot worse than you thought....). You can always shorten a seat pin but making it longer is much more difficult. If you are to shorten a seat pin there is something to be said for slash-cutting it so that the front is longer than the back; this makes the tip of the seat pin slightly more flexible and makes the stresses less localised where they are transferred into the frame.

Thompson seat pins are light and clever in some ways but even their 'layback' model has no real layback and the aluminium alloy they use is completely unsuitable for UK winter use; it is difficult to find a commonly used aluminium alloy that corrodes more readily. IIRC they also say to throw their aluminium seat pins away after 10000 miles or something. Mechanical fuses are all very well but if the enemy is fatigue they are about as much use as a chocolate teapot.

cheers

Thanks. As I'm aiming at titanium cutting it later might not be that easy. I've noticed that the Van Nicholas seat pin has the bottom cut at an angle already. Some users elsewhere have mentioned the Van Nic seat pins bending under stress, though usually riders heavier than me.

That Moots looks nice, but at €350, a bit rich for me. Do you have an opinion on the USE Sumo/Duro? Or a reliable aluminium if you don't think much of the Thomson.

Thanks

[NickJP]

Lynskey make a 25mm setback Ti seatpost, though I think the clamp is aluminium. But I wouldn't worry about it having an aluminium head - I have an early 1990s Campagnolo Record seatpost with Ti shaft and Al head, and it shows no signs of deterioration after almost 30 years of fairly constant use.

[Brucey]

5" of seat pin showing isn't a lot. IME most aluminium clamp parts last longer than the saddle rails that are attached to them. You could look at the seat pin as being a consumable part; one which doesn't last forever but doesn't cost a fortune either. One that can easily be removed, inspected for cracks or other damage and replaced if necessary.


The main benefits of Ti seat pins are that they are lightweight and that they can be built so that they flex appreciably. But the light weight isn't a very big deal on most touring bikes and 5" of exposed seat pin doesn't allow for much benefit from flex.

So unless you think you are likely to break the seat pin for some reason I wouldn't agonise over it too much. If you buy one that is expected to last a reasonable time when there is ~10" showing out of a compact frame, it'll probably last a lot longer when (it is cut down if necessary) there is only 5" showing.

Cutting a Ti seat pin might take a couple of hacksaw blades but isn't too bad. Just use oil in the cut, cut slowly with plenty of pressure downwards and the blade will last longer.

FWIW I think the sumo design is quite strong; better than the other USE offerings.

cheers

[ElCani]

I have a Van Nicholas one of the same design as the Moots above. It has held up very well over about eight years of use.

[pwa]

I've had a few seatposts fail, and it has always been the tube that has snapped. I'd not worry about the clamp being bonded-on ally. Perhaps of more concern is the slim, flimsy looking bolts used on some clamps.

[alexnharvey]

I'd like a nice stainless steel version of that moots post, maybe 953.

[Brucey]

one of the options for a road bike with ~5" showing is a campag record/chorus model from the late 1990s. Ti post with aluminium clamp. I have one of these in my road bike; in the throes of a titanium frenzy, I bought it used about fifteen years ago, and I thought it was expensive then, even though the one I bought needed a good polish. I just looked on e-bay and there were a few on there but the asking prices were stratospheric; over £200 a pop...

cheers