what's the best 27.2 seatpost for abit of flex then people ?
my old easton ec70... you can see it move!
I got an FSA carbon post of on-one for £20 last year. don't know how it compares to other carbon posts but it's much flexier on the same bike than a Thomson.
I would like a carbon seatpost ...yummy 🙂
CFRP (Carbon Fibre Reinforced Plastic) was originaly developed as a material with a higher stiffness to weight ratio than aluminium, steel, titanium.
Is bike carbon fibre different from CFRP?
http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=89&pageid=2144417038
Let me guess, you're one of these people that starts conversations 'well I'm an engineer' at which point no one listens to you anymore!
But many carbon posts are lighter than their alu counterparts, so yes the stiffness to weight may be the same, but less weight = less stiffness surely?
Aside from the fact that seatposts invariably aren't made of a perfectly round tube and thus are more able to flex.
i've got a 27.2 carbon post on my sanderson and its rather flexy in a very nice way. It used to be on a very stiff aluminium race HT and was a real bonus!
Titanium.
I had one a few years ago and it flexed considerably; made things much more comfortable for longer rides on a hardtail. Only sold it as it had too much layback.
my thomson was always a bit flexy
Is bike carbon fibre different from CFRP?
No of course not. Carbon Fibre is just the term that's used in the bike (and most other) industry rather than CFRP which is typically used by overly @nal engineer types 😉
Stiffness to weight isn't the key attribute here but rather how far you can elastically deform (eg flex without permanently bending/breaking) the seatpost without either fatigueing or bending - carbon does this better than aluminium so it can be designed in (along with typically less weight)
Talking from my own experiences, it also seems to damp out vibration better than metal tubing.
+1 Titanium
I've got a mate who had a Carbon Scott Team Scale with the integrated seatpost
that flexed a lot, he's not a small chap
anyway long story short snapped it clean off within about 2 months
frame fubared!
moral you don't want carbon to flex too much, buy Titanium if you want that
Titanium can break too though...
Well generally, lighter posts will have thinner walls and thus flex more.
So... get the lightest post you can. Personally, having used a 130g New Ultimate seatpost for 18 months I don't really see the flex thing! Maybe I should try a Thomson for comparison!
I've got a Van Nicolas Ti 27.2 post.
First time I rode it was like letting 10psi out of my back tyre - I had to keep checking I hadn't punctured.
would recommend Ti post to anyone looking for some cush without going for a suspension seatpost.
I've got an alloy Control Tech on my Inbred that virtually bends in the wind! I've shown people how much it flexes and they are amazed. It must be 20mm+ of movement at the top.
moral you don't want carbon to flex too much
Rubbish. What you meant is you don't want carbon to be either badly built or stressed beyond what it's designed for. Same as any Ti, steel or alu component...
+1 for the Van Nic Ti post
It was like getting a new bike when I fitted one on a hardtail and still have one on my CX bike
Oscar Pistorius has flexy CFRP legs, but even they break some times. A credit to the man's resilience is that he never seems to see this as more than a minor set back.
CFRP is fairly strong in tension, but not so good in compression.
Also fracture toughness of CFRP is not so great.
"my old easton ec70... you can see it move! "
I'd agree. I had a layback 26.8mm on my RM Vertex and for the first few rides I kept thinking I had a flat rear tyre. It really was noticeably soft-riding.
moral you don't want carbon to flex too much
Try bending a fishing rod. They're carbon. 🙂
Carbon: It just depends if it's designed to flex or not, nothing else.
Do people still use Thudbuster or USE suspension seatposts?
To be fair, Oscar Pistorious breaking a leg has less devestating concequences than Usain Bolt breaking a leg...
Never seen the point in suspension seatposts, how do they not trash your knees!?
http://www.lhthomson.com/carbon_seatpost.htm
http://www.specialized.com/es/en/bc/SBCEqProduct.jsp?spid=41851&menuItemId=0&eid=0
"advanced composite weave combines high strength and stiffness with excellent comfort"
stiffness with comfort........... now that is advanced !
also, High modulus = stiff