Seat post rack.

[Ajax Bay]

Presumably no @further than https://www.google.com/maps?q=Glastonbury+Somerset

 

[further]

This /\

 

[Incontinentia Buttocks]

Maybe a tad out of my way!

 

[jay clock]

I have one of these,free if you pick it up,t's missing the rubber spacer.
View attachment 125782

I have one of those and they are not bad at all.. Nice that you can change the angle. However a little narrow, and it also has a rattly little tool tray, and as a result I have just bought this bag https://www.rosebikes.co.uk/product/detail/aid:24816 and this rack https://www.rosebikes.co.uk/article/xtreme-rack-sp-seat-post-carrier/aid:50971 and they appear excellent. Not actually used them yet but have a 4 day ride to Cornwall in May. Worth saying that the clamp is very firm and would not be any good for a carbon seat post

I do have full touring set up on my tourer but the above set up suits my lighter winter bike

 

[MichaelW2]

Work out the weight/volume ratio of various bag systems. Rackless saddlebags, or ones using mini racks are usually more efficient. One saddlebag can carry the same as one med size pannier. Saddlebags are also aerodynamically efficient and put less stress on your bike.

 

[mjr]

Saddlebags are also aerodynamically efficient and put less stress on your bike.

Can you explain why? I think hanging weight off the saddle rails would be more stressful to the bike, especially modern long-seatpost designs, although probably well within bounds for most riders.

Also, aerodynamics seem similar for all but the largest panniers: both are mostly hidden by the rider.

 

[MichaelW2]

Can you explain why? I think hanging weight off the saddle rails would be more stressful to the bike, especially modern long-seatpost designs, although probably well within bounds for most riders.

Also, aerodynamics seem similar for all but the largest panniers: both are mostly hidden by the rider.

Saddlebag weight travels through the seatpost, the same as rider weight. Cantilevered seatposts act as a lever trying to crush the post. Some lightweight posts may not react well to a cantilevered load, esp the peak load over rough ground. Making the seatpost clamp large enough to spread the load adds weight.
Saddlebags sit in the disturbed air behind a riders upper thigh. Panniers sit below knee level, further back from the legs and wider, so create a separate disturbance.
Given the low load specs, high weight, and poor attachment design, what does a clamp-on rack+panniers have to recommend itself?

 

[Ajax Bay]

Given the low load specs, high weight, and poor attachment design, what does a clamp-on rack+panniers have to recommend itself?

I agree with @MichaelW2 's implicit answer to his final (quoted) question: very little.
Without going weightweenie, I've just rechecked a few weights for my stuff, YMMV.
A seatbag (mine's a Raleigh which I think is an imitation of a simple Carradice (11 litres)) is 405g. I use a rear QR to secure it to the Brooks (add 101g) but could actually just strap on (=0g).
The clamp-on (to seatpost) rack is 458g and a lightweight rack bag is 538g (it's a type with the mini foldout panniers, if you wanted to risk them - they don't hang down as far as the wheel and might be useful for the evening shop before getting home or to the overnight stop - bought it but never used (because of the factors listed below)). The carrying level is rather higher than a normal rack, btw.
A 'normal' aluminium rack (mine) is 538g with fittings and each pannier (again Raleigh, Ortleib or the like rather heavier (and better!)) weighs 784g. Of course the normal rack options has lots of expansion potential with a second pannier and significant carrying capacity on the rack itself.
Seatbag: 405g
Seatpost rack and lightweight rack bag: 996g
Rack (normal) and one pannier: 1322g
So if you want to carry more than 5 litres at the rear, a saddlebag is a better choice than a seatpost clamp-on rack and whatever you strap on it, for:
1) weight
2) stability
3) aero (argument made in above post)
4) possibility of getting your leg over the back with a greater measure of assurance - especially when tired.
5) Aesthetics (Edit: added)
I would be interested to hear other perspectives.

 

[mjr]

Saddlebags sit in the disturbed air behind a riders upper thigh. Panniers sit below knee level, further back from the legs and wider, so create a separate disturbance.

A seatpost rack wouldn't put panniers that low... if you even wanted to risk panniers rather than just a rack bag. I think that's being rather dodgy in choosing what to compare a saddlebag with.

Given the low load specs, high weight, and poor attachment design, what does a clamp-on rack+panniers have to recommend itself?

Although poor, the attachment design of bag onto beam rack is still tons better than most saddlebags which are just an incredibly annoying faff, even when you have supposedly-compatible saddle and bag, such as Brooks and Carradice. Even then, the bags naturally want to rotate into the backs of the rider's legs, so you add a support rack and before long, you might as well have added a multipurpose rack instead.

Either go for a seatpack or fit a rack - don't mess with Mr In-between.

View: https://www.youtube.com/watch?v=5EpUea6fmG4

 

[contadino]

My Carradice bag now sits on a Nitto R10 rack. Higher up than panniers, but supported from below so that a) bag doesn't rub on tyre and b) bag stays in place (unlike with the Carradice Classic Rack and the Carradice SQR which both failed.)

A few hundred grams of weight isn't hugely important to me otherwise I wouldn't carry most of the stuff I do or need a saddle bag.

 

[PaulSB]

One thing to keep in mind is clearance over the wheel and if you have enough exposed seat post to mount it.

I'm short and only have limited room between saddle and frame. I've often wanted one of these set ups but all those I've tried simply don't fit through lack of space.