For as long as I can remember, I have had a strong belief that the opening in a seatpost collar should align with the slot in the frame. I am quick to show customers the error of their ways when this is not done. My thinking is that in order for the seat tube to effectively clamp the post, it must close at the slot, and in order for this to happen when the collar opening is opposite the slot, there has to be some sliding of the collar over the seat tube while the collar is tightened at one side and the frame slot closes at the opposite side. This seems like a huge amount of friction and inefficiency that can be avoided by lining up the openings on the same side, which would enable them to close together with no sliding necessary.
However, I have just come across these in a Fox Transfer seatpost troubleshooting guide:
They seems to imply that the collar and frame openings should be opposite each other. Can someone explain the reason for this? Have I been wrong all along?
My client yesterday was just complaining about how sensitive the Fox Transfer dropper is to seatpost collar tightness, and this advice from Fox sounds specific to resolving dropper friction issues.
In general use with non dropper posts, this is probably going to be one of those personal preference / bias things, like bar tape wrapping direction.
I think the seat tube will stay rounder if the collar split isnāt lined up with the seat tube slot. I base this on a thin wall tubing frame designed to use a shim and clamp on F Der, where the shim spread out the clamp force and the builder said to put the split in the shim shim opposite the F Der clamp bolt bc lining them up had a greater tendency to dent the tube.
I wonder about this every time I fit my separate seat post clamps. Personally I prefer @Babs reasoning and I like the idea of spreading the compression a bit by fitting the clamp opposite the frame slot. I have no evidence to back up my gut feelings.
Iāve always used the collar the traditional way. Does anyone make a ābackwardsā one where the bolt head is on the drive side? A whole new market!
I think itās pretty clear that the offset of the bolt to the circumference of the clamp causes higher stress next to the gap in the clamp than elsewhere. Having the frame continuous not slotted at this point will spread the stress more evenly on the seat post. Question is whether the frame or the seat post is the priority. A dented post is an easier replacement than a dented frame but at 4-5Nm torque in the bolt Iām not expecting either one.
Iāve definitely seen it recommended to put the clamp slot opposite the frame slot - not 100% sure but I think this was on the leaflet that came with a seatpost clamp (Salsa lip lock).
Out of interest, where have you seen this? I believed you, but knowing Hope to have good technical documentation I was curious to read their wording and see if they provided reasoning. However, what I found says the exact opposite: āIf present, align the (or one of the) slot of the frame with the slot of the clamp.ā
Like @Nick_Coward stated, I just donāt think it generally matters at the torques required typically for 99.9% of users. The other 0.1% are riding Darimo or Fox Transfer posts and then it might be a consideration haha.
My priority when aligning it are:
Logo is either forward or driveside
Bolt is accessed driveside
Both superseded by any instructions from manufacturer if provided!
In my experience over the years, less grit and crud can accumulate in the slot of you opt for the āoppositeā orientation. If I remember correctly, Campagnolo used to manufacture a collar with a 45 degree angle to distribute the stresses more evenly but it also helped to avoid the issue of dirt ingress.
Really want to know? Buy two bikes, two orientations and ride them alternately for 20 years and you might end up with a conclusive answer!
Thank you for your enquiry. The instructions showing the clamp with the slot lined up with the frame is outdated, looks like we didnāt get round to changing the instructions!
In theory, for best load distribution it is best to have the slot opposite the frame slot as this puts a more even squeeze around the seat post.
When fatigue testing we tried the clamp in both positions though and didnāt find any significant difference so you could fit it either way around really.
Thank you for this. Thatās a nice source of feedback, and probably as definitive as weāre going to get.
Iām going to stop ācorrectingā people, and will weigh up the practical and aesthetic aspects too when Iām selecting which orientation to use in future. In the case of sticking dropper posts Iāll revert to positioning the slot opposite the frame slot.
