No sag here. I have the Trek Interchange DeLux Trunk with a seperate Interchange rack on my 930 and 520. Not suitable for serious touring but excellent for commuting or long day trips. Just click-n-go. Normally, I have the trunk full of the usual What-If stuff, plus lunch. The right pannier rarely gets used unless I go for a long trip and the weather is iffy. Even with the left pannier full, there is no sag. I think the connection is: Buy a lightweight bag, get the sag. Or, don't be a weight weenie, get the tool that'll do the job.