ClarkinHawaii

<edit> picture removed </edit>

Now that I have your attention . . .

Should the gap in the seatpost clamp line up with the gap in the seat tube, or should it be 180 degrees away?

Bonus question:

Rookie installs new rear derailleur onto hanger with grease on threads rather than threadlocker. OK this way, or should it be removed, threads degreased, and reinstalled with blue loctite?

Shimagnolo

What seatpost?

RonH

Yes.

Bonus: Do whatever you want. FYI: I've never seen locktite on the derailleur bolt threads.

fietsbob

I just use Loctite on Bolts I think might rattle loose, like holding the rear rack on, never the derailleur mount to hanger .
its a big bolt .

bikeman715

grease is the way to go for the bolt.

Retro Grouch 

Line up the gap in the clamp with the gap in the seat tube.

In fact, Santana tandems has two separate part numbers for captain and stoker seat tube clamps. The slot in the captain's seat tube is in the front so the clamps have to be threaded on opposite sides or the bolt heads would be on opposite sides of the bike.

tj90

Conventional wisdom is to line up the gaps, but I seem to remember in some installation instructions that Easton(?) recommended opposite orientation to reduce the "cutting" of the frame edge into the carbon tube. I guess with the gaps line up, the seatpost sees more concentration of stress in the back? Maybe placing the clamp with the slot toward the front puts less stress on the bolt since the bulk aluminum clamp - and not the bolt - is taking a majority of the stress as your ass loads the seat cyclically.... It may also prevent the bolt from backing out as well and creaking.

Some newer design seat clamps purposely bias the gap slightly shifted from the slot cut into the frame. See pic. The white arrow is lined up to the frame slot. The bolt is also threaded into a pivot to reduce bending stresses on the bolt as its being torqued down. Pretty clever design. Look at all that aluminum directly behind the frame slot where stress will be the highest.

Honestly, I dont think it matters too much. Since I run carbon all the time, Ive stuck with the recommendation I read on some installation instructions years ago. Its always fun to see some pimple faced 18 YO bike mechanic "dress me down" with my incorrectly installed seat post clamp.

Thinking about all the stresses iit seems that frame manufacturers would want to put the slot toward the front... Hmmm...

thirdgenbird

metal seatpost = line up gaps

carbon fiber seatpost = gaps 180 degrees apart

gt35built

Its most common to line them up, however I've noticed on some of the bontrager clamps with rack mounts that they are cut slighty off centered to the sea tube slit.

Locktite would be ideal if it comes loose while riding, but doesnt seem like something necessary. Never grease the bolt either, but a little wouldnt hurt.

ClarkinHawaii

This is my favorite response--I mean, it sounds like it's probably correct, but like, Why? If it's a metal frame and a carbon seatpost, then I can understand the "digging in" deal.

If you look at the numerous "show us your bike" threads, they are pictured both ways. Both kinds of seatposts and no way to tell which is which.

My situation is carbon frame and carbon or alloy seatpost. If I read you all correctly, it doesn't matter at all**********

With regards to the rear mech on the hanger, the loctite is something I've always done, not necessarily because I think the bolt is going to loosen, but rather because the results are so catastrophic if it does. Sort of like using a dork disc.

BCRider

I'd suggest that the type of seatpost will determine which way to do it. While the carbon frame material won't dig into a carbon seat post it could still produce higher pressure spots at the rear. By aligning the clamp slot to the front the more accurately rounder shape opposite the clamp screw and slot will cradle the frame slot and post more equally all around so the pressure will be more even. And with anything carbon you want nice even pressure spread over a greater surface area.

thirdgenbird

It has to do with spreading out the clamping force. With a carbon post (in any frame) you want the clamp turned 180 degrees or an offset clamp. Aluminum is not as picky.

Stems clams are being made offset now for the same reason. It changes it from a "pinch" force to a more even clamp.

You will see them both ways but that does not make it correct. Ask most seatpost manufacturers. Campagnolo posts come with the offset style clamp but directly state if its not used the traditional one needs turned around. I believe several other companies agree.

ClarkinHawaii

OK, I'm sold. I've also had the thought that a thin film of grease on the inside of the clamp would help even out any pressure irregularities. That is, between the clamp and the carbon seat tube end, NOT between the seat post and the seat tube.

This is so well worded--I was thinking along these lines but was unable to articulate it as well as BCRider: "I'd suggest that the type of seatpost will determine which way to do it. While the carbon frame material won't dig into a carbon seat post it could still produce higher pressure spots at the rear. By aligning the clamp slot to the front the more accurately rounder shape opposite the clamp screw and slot will cradle the frame slot and post more equally all around so the pressure will be more even. And with anything carbon you want nice even pressure spread over a greater surface area. "

tj90

I agree with you, BCRider and 3rdgen summarized it well - avoid pinch forces with carbon. Probably why handlebar to stem interfaces are better with 4 bolt removable plates than with the old style single bolt that would pinch the handlebar. Those old quill stems would gouge aluminum - I imagine they would be disastrous with carbon bars!

thirdgenbird

thats a great example