Joined: Aug 2010
Posts: 12,727
Likes: 2,105
From: Madison, WI
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
For rear panniers, if you get larger panniers than you really need, you have the capacity if:
- you decide to carry some extra water bottles or
- if you buy some extra bread for a picnic lunch or
- if you get the urge to buy a six pack or
- etc.
The front Ortliebs at 25L are a good size for one reason - it forces you to avoid putting too much weight on the front rack.
If you really are considering that small of a set of panniers for the rear for credit card touring, you might also consider getting one of the rack trunks that have zip out mini panniers. I think the combination is even larger volume than the front Ortliebs and they are quite light. They also work well around town as a normal rack trunk when you do not need the extra volume you get with the panniers.