Seat Clamps - how tight is too tight?

[Barneyballbags]

I've currently got a couple of posts up in the wanted section, following a bit of a 'mishap' that I had today with my Kona Racelight Tahoma seatpost.

I fitted a new saddle, and was dull enough to do the dreaded 'one last tweak' on the allen key to tighten the seatclamp... Unfortunately that one last tweak proved one too many for my poor seatclamp and it gave way with a loud bang

Much swearing later, it got me wondering how tight other people have their seatpost bolts? I don't have a torque wrench so I tighten 'by feel' and it hasn't let me down in almost 20 years....until now.

Do seatpost clamp bolts need to be mega tight, or is it a case of tightening them and then just 'tweaking' each bolt once to finish?

I'm just paranoid that I'll do it again with my new seatpost (when I find one!) now!!!

 

[sylus]

I normally put a bit of blue loctite on the bolt thread then do it up till it's stopped being easy then add a 1/4 turn. This normally gets the seat secured and the blue loctite helps

 

[mechagouki]

If you have the right size post you should not have to crank down the clamp to stop it from slipping - a correctly fitted post will slide smoothly into a greased seat tube with very little effort and should stay put with only a firmly tightened QR. There is no specific torque for this as different size and material have different shear strengths, but you shouldn't have to use excessive force. If you're sure you have the right size post and it is still slipping try applying a coat of carbon-prep to the post instead of grease.

EDIT: just re-read your post and realised you are talking about the saddle clamping mechanism - right? Again, there is no specific torque (too many clamp designs), just tighten in increments until you can't move the saddle whilst gripping it firmly front and rear.

 

[marc two tone]

too tight

ha ha. popped bolts myself tightening up. making sure all is solid!

now, i tighten up until i cant rotate the seatpost using the seat as a lever. at this i dont use brute force but, a good push and pull. no movement and im happy! the pressure in the seat tube at this stage should hold the rider easily as the rider shouldn't be able to apply a twisting motion anyway. i have never torqued a bolt up...ever.

and a light smear of grease is all that's needed on the seatpost.

 

[Barneyballbags]

Re: too tight

ha ha. popped bolts myself tightening up. making sure all is solid!

now, i tighten up until i cant rotate the seatpost using the seat as a lever. at this i dont use brute force but, a good push and pull. no movement and im happy! the pressure in the seat tube at this stage should hold the rider easily as the rider shouldn't be able to apply a twisting motion anyway. i have never torqued a bolt up...ever.

and a light smear of grease is all that's needed on the seatpost.

Sorry, I should have made my original post clearer - I mean the seat clamp bolts (that hold the saddle)

 

[MiniNinjaRob]

Pics please to complete the shame!!

 

[marc two tone]

Re: too tight

ha ha. popped bolts myself tightening up. making sure all is solid!

now, i tighten up until i cant rotate the seatpost using the seat as a lever. at this i dont use brute force but, a good push and pull. no movement and im happy! the pressure in the seat tube at this stage should hold the rider easily as the rider shouldn't be able to apply a twisting motion anyway. i have never torqued a bolt up...ever.

and a light smear of grease is all that's needed on the seatpost.

Sorry, I should have made my original post clearer - I mean the seat clamp bolts (that hold the saddle)

yes, its in there i just missed it nice and tight will do. until the allen key starts to hurt your hand

 

[Barneyballbags]

Pics please to complete the shame!!

Awwww, ok...

Minty post:

Not so minty clamp:

 

[02gf74]

I don't have a torque wrench either and it is down to experience.

seat post clamps vary as some have M6 or M5 bolt and depending on type of post - alloy or carbon, limits how much you can tighten them.

I generally use 2 fingers and thumb on an allen key until it is getting really quite tight i.e. don't put the key in the ball of my palm that allows much higher torques.

Being of the larger build, I have had trouble with posts slipping so after the above tightening, I mark the post with tippex and go for a ride. If the post stays put after 10 miles, then job done. If it slips, I undo the bolt making note of inital allen key position and counting turns, move post back up then do up post but give the bolt about 1/8 more turn.

Eventually the post will hold.

There was one case with carbon fibre post in a rod bike that started to shows signs of stress - I fitted a short section of copper plumbing tube on the inside of the post that fixed it (wanted to keep the carbon post fo the blingage).

Another instance was with a Hope clamp with the large alloy bolt whihc would not hold my post and the alloy bolts started to stretch; obviously this was never going to hold - so I used a steel bolt and made the specially shaped alloy cam nut and that is fine.

Same principle applies to saddle clamp - I have lightweight Merek carbon post which has carbon fibre/resin seat rail clamps (usaully they are alloy) so did not know how much I could tighten those - by drawing lines in tippex on them and the rails I could see if the seat slipped and tighten a little bit when it did was how I sorted that, plus a bit of roughening up on the inside of the clamps.

This may not help you but you get the general idea - you can keep tightening a bolt and can get a feel over time how far you can go - go too far and the resistance decreaes as the bolt stretches prior to failing.

 

[MikeD]

That style of clamp, not all that tight - after a certain point you're just bending the top bit. If you can't move the saddle, that's tight enough.