sysrq

According to pressure pattern transfered trough the inner tube wrapped around the rails looks like most of the pressure is concentrated in the central area of the clamps. Never had such a problem with cheaper seat posts.

fietsbob

some seat post clamp heads deform to a point where they no longer grip the saddle rails..

A more expensive seat post, of same diameter (Measure) will grip better..

one combination ; a common tubular seat post and Brompton's saddle clip on top 'the pentaclip' ..

combo is about $50. steel saddle clips cost a lot less..

Others have their own favorites to offer .. you need to know post diameter .. they increase in size by .2 mm increments..






over...

sysrq

Well, looks like more expensive seat posts like Suntour NCX can't be used without torque wrench since it's theoretically impossible to overthighten it with a standard length Allen key. This one needs up to 18 Nm of torque.

fietsbob

Looks = need pictures... My old favorite the

fietsbob

ok one of these.. why do you feel a need for the rubber?

sysrq

Cause I'm not sure if carbon assembly gripper compound will work in such a small surface area.

fietsbob

If the saddle rail is too thin, wrap it with aluminum, cut from a drinks can as a shim sleeve,

to increase the diameter of the of the saddle rails...

I measured 2 steel saddle's rails are 7 mm Diameter, My 1 Aluminum rail saddle a Turbo is 8 mm rod..






...

sysrq

Mine are 7 mm and painted, previous ones were chrome plated or chromoly and didn't slip.

fietsbob

if steel maybe add texture to them , vibrating engraver? center punch? red try loc tite?

sysrq

Tightened by extending the Allen key with a 7 inch pipe now.

Not sure if I will be able to hold the center punch on such a small round area without slipping. Otherwise that seems to be the best approach without removing any material from the rails despite the fact that indentions could weaken the steel.

dsbrantjr

Why not try some coarse valve grinding compound? It is harder than steel and should dig in nicely.

sysrq

If only I had one on hand, otherwise hard to justify spending on it for single use only even it's cheaper than a carbon assembly compound. As always car stuff turns out to be cheaper than anything inten to be used on a bicycle.

dsbrantjr

<$5 to make a >$100 seatpost usable sounds like a decent deal to me. https://www.amazon.com/Permatex-8003.../dp/B0002UEOMS
You could mix some sand with a little grease and try that.

To your earlier observation, he pressure is concentrated at the center of the clamps because that is where the clamp bolt is.

sysrq

Gonna try this one.
https://www.amazon.co.uk/Chemico-033.../dp/B006ZXZYMA

Normal sand seems a bit too coarse for this application, might be even too brittle. Earlier tried to remove some sand from a sand paper with unsatisfactory results.

Depends on the shape of the clamps, some of them have a narrow contact points at the ends, this one has at the center which makes it hard to achieve a proper pressure distribution by amateur standards.

sysrq

Looks like after applying coarse lapping compound and torquing heavily greased bolts to 18 Nm it doesn't slip anymore. Thread closed.