Just a quick Q on seatpost bags. I'm encouraging a lad to get one for a trip to London in the coming months. He tells me that they all have a disclaimer on the info for many seatpacks that they're "not recommended for carbon seatposts"... Is that just the seatpost bag manufacturers covering their backs in case someone decides to carry the kitchen sink or is there mire to it??

Thanks in advance!

Can't see how adding a kilo or two will all of a sudden damage the post.

Used harnesses on carbon bars for the last two years (and the straps are tensioned between the bar and fork) and so far, so good!

If he's that worried, buy a cheap alu post for luggage

Maybe it's not the weight, maybe it's the inherent scratching and scuffing a seatpack will do to the post ... carbon's very soft* and it doesn't take much to cause a stress raiser which could result in sudden snappage.

However, an old tube or tape should stop it.

*when compared to aluminium
*soft isn't really right word but in this instance it makes sense.

I'm using gaffer tape. Easy to get on and off, very tough. Have it on the seat rails and the post.

The abrasion effect to the carbon would be no greater than if the seatpost/bar were made from aluminium! I've been using bag's strapped to carbon for a few year's now and apart from a little scuffing I've had no problems and I'm not worried about the carbon failing. I think memories and story's from the early days of carbon use in the bike industry where failures were more common is still lingering.

I used a carbon post on the TNR, as Stu has suggested I cut off an old tube, slid it over the post and it was completely unmarked on my return.

The abrasion effect to the carbon would be no greater than if the seatpost/bar were made from aluminium!

Place a piece of carbon seatpost in a vice and rub it with a file or hacksaw, now do the same to a aluminium one ... there'll be a marked difference. There's also a difference to how the two materials respond to nicks, scratches, etc.

Bearbonesnorm wrote:

The abrasion effect to the carbon would be no greater than if the seatpost/bar were made from aluminium!

Place a piece of carbon seatpost in a vice and rub it with a file or hacksaw, now do the same to a aluminium one ... there'll be a marked difference. There's also a difference to how the two materials respond to nicks, scratches, etc.

^^^^^^^ That.

There's no way I would use a seatpack on a carbon tube without protection. Likewise, a carbon frame without protection.
I used a carbon frame on the TNR, protected with hell tape. Without it given the dust and gravel I'd have come home with a frame like a tea bag.

I recommend against using a seatpost on a carbon post. I did and now my post looks like its been sanded down where the seatpack was (by quite a bit!). As suggested putting some tape on the post solves the problem. I used electrical tape afterwards which is a lot easier to get off than say duck tape

Bearbonesnorm wrote:

The abrasion effect to the carbon would be no greater than if the seatpost/bar were made from aluminium!

Place a piece of carbon seatpost in a vice and rub it with a file or hacksaw, now do the same to a aluminium one ... there'll be a marked difference. There's also a difference to how the two materials respond to nicks, scratches, etc.

I have many times and know how easy it is to remove material with tool's made for removing material but the carbon is made with a layer that is meant to take scratches and dinks and protect the more structural layers coming underneath.

There's nothing wrong with taping your post's/bars to protect them from scuffing but if you have decent parts then the bags won't effect the integrity of carbon! Just an opinion!

It'll be fine. Stop overthinking.

GregMay wrote:It'll be fine. Stop overthinking.

That's certainly my experience

GregMay wrote:It'll be fine. Stop overthinking.

https://flic.kr/p/RbYNwE
This is after a couple of 5 mile commutes. The shiny surface has been completely removed. Just put a couple wraps of tape around your post first.

MarkW wrote:

GregMay wrote:It'll be fine. Stop overthinking.

https://flic.kr/p/RbYNwE
This is after a couple of 5 mile commutes. The shiny surface has been completely removed. Just put a couple wraps of tape around your post first.

Nothing to worry about there, Greg May & ScotRoutes are right it's over thinking the issue, if you are bothered about about your post/bar being scratched/scuffed then by all means tape them up otherwise don't stress!

I've used a seatpack on a carbon seat post a few times, still here

I would certainly use a bit of sacrificial tape - the negligible extra weight will at the very least provide peace of mind, and might even stop your post from being damaged. I managed to almost wear through a carbon Lefty in one day of riding (badly routed cables) - the old Kielder 100, in 2011, a particularly wet day where an astonishing amount of abrasion damage took place, particularly to CF components.

I think it was Lael Wilcox who trashed a new CF frame on the TD from abrasion.

I have many times and know how easy it is to remove material with tool's made for removing material but the carbon is made with a layer that is meant to take scratches and dinks and protect the more structural layers coming underneath.

I'm not sure there's much difference between something like emery paper and a gritty wet saddlepack and emery will remove carbon an awful lot quicker than it'll remove aluminium ... protective clearcoat layer or not.

Thanks all... my buddy has hopefully come to his senses and will get himself a shiny Revelate Designs Viscacha...