I used a Nelson for commuting for many years and it was perfect for that. That might be the size of bag you want to go with...15 liters. Now that I'm retired, it is my grocery carrier...I can get a gallon of milk and a bunch of bananas in it!
I also use a Pendle which is sort of a downsized Nelson...11 liters. That may well work for you and it also makes a good size for winter day rides, but it might be too small for your needs.
I don't know how much space you have between the saddle loops and rear wheel, but the Nelson hangs down about 8 inches from the saddle loops, (a Brooks B-17), while the Pendle drops down about 6 1/2 inches. These are rough measurements based on observations in my cold, dark shed so take them with a grain of salt.
Hope this is of help!
George in NoCal
On my touring bike, I carry the heavy stuff in a pair of front panniers, and just pack bulky lightweight items in the saddlebag, so I use a bagman quick release rack. It specifies a weight limit of 10kg. Here's the touring bike with a Carradice camper longflap saddlebag - front panniers and handlebar bag are Ortlieb:
If i could point to one perfect size, it would probably be the nelson. The expandable long flap would be great for touring. But there's a version without side pockets (can't remember name) that'll be the next one I buy. I find the pockets stiff and hard to use, not secure enough for small things, and cumbersome the way they protrude.
Bottom line suggestion is to get the biggest one (within reason) that fits your available space. There's so little difference between weights when empty, that there's no reason not to have the available capacity.
Also agree that they work better with a bagman or similar support. Ocean air cycles is doing a new batch of their improved version soon, together with nitto and blue lug - fyi.

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I'm doing a little 2020 motive and opportunity Jenga in my head, and considering taking a 650b Fuji S12-S on a short tour this summer. I've got a big Rando bag and front panniers figured out, and figured I'd pick up a Carradice saddle bag to carry the lighter and bulkier stuff. Never having seen a real British saddle bag I'm not sure how big a bag to go with. I don't want to get to large of a bag that will only get used for one week out of the year, or will over load the rear of the bike. I've got the saddle pretty low with a fistfull of seat post and all that but, I ordered a VO rear constructors rack so I'm not concerned with the bag pushing on the fender. I'd be interested in hearing folks thoughts or seeing some pictures of this sort of set up. Thanks, Woody
Craig in Tucson
"You'll find that a lighter front end on a well-balanced bike is more fun anyway"



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On Jan 4, 2020, at 1:43 PM, Mark Bulgier <ma...@bulgier.net> wrote:
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%20in%20Full%20Regalia.jpg?part=0.1&view=1)
Photo #2 Well-balanced bike. '96 Waterford built Riv All Rounder 650x47's. No tail wagging! Climbed many Arizona backroads with loads biased rear, biased forward as you can see. Stable as a train. 42mm trail. Can handle 60/40, 40/60 or 50/50 weight distribution with aplomb.


Photos #3 and #4 Very well-balanced bike. '99 Jack Taylor Tourist (this alone says it all). First is S24O configuration.Not a wag. Light and sassy front end. Fun. Second pic: Fully loaded like this I can fall asleep climbing and wake up at the top of a hill...riding straight. Out of saddle stability. Trail in upper 40's. Usually do a 60/40.

Photos #5 and #6 Here's a gem. '65 HR Morris. Master craftsman. As you can see, it goes both ways and either set up is stable. Getting my point Mark?

I have 2 or 3 other tourers that handle rear loads in combination with front, but why belabor the point? I also have a couple of non-touring bikes I would not load with any panniers anywhere. I've found that all geometries can pretty much handle a saddlebag.

This is NOT a photograph of an inexperienced bike tourist. Note the smirk. Or is that the smile of satisfaction that comes from riding a touring bike that handles beautifully with a rear load?
Craig in Tucson
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That's for sure. Some very scary pix IMHO.
Back in the 1980s the default for hostel touring in the UK was just a Carradice saddlebag, nothing else, and usually not a huge one either.
Later,
Stephen
PS: http://ultralightcycling.blogspot.com
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Later,
Stephen
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> [snip] Hwy 1 in NorCal [...], there was a guy going south (wrong way-headwinds!)
I planned my trip from Ft Bragg to Jenner going south. That worked well.
George in NoCal
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Mark Guglielmana wrote:... I was very happy about that, because I had the ocean-side views all the way down. Splendissima!Mark B in Seattle
Nick
Nick