I have seen this done before and often wondered why in the heck someone would do this to a saddle...and here I am doing it.
First of all, there is a very good reason for doing it. Second of all, not everyone should rush out and do it.
I have enjoyed the feel and performance of a fine leather saddle for some time now. Recently I acquired this new Brooks Swift model which is a bit narrower than the B-17 that I have used in the past. While I like the narrower profile, lighter weight, and generally stiffer shell, I have noticed something in recent weeks.
I believe that this problem (I am about to explain) tends to happen more on narrower leather saddles probably as a result from the tighter bends in the leather (and less leather present to distribute the load). The problem is, when the sit bones press hard into the saddle, the leather is forced to flatten out (or bow). The sides of the saddle are folded down to give the leather structure (to resist being a hammock that your butt sits in), but the constant beating a saddle takes on a MTB can cause these sides to bow out or rise up.
Compound the bowing with the fact that he plate under the leather (that the leather is riveted to) has a folded shape also. When the leather is stressed and begins to bow and turn up, the plate holds it down at the point of the rivet and a crease will begin to form in the leather...once a crease forms, the structure of the leather is compromised (perhaps irreversibly).
Taking a look (above) at the Swallow model (the narrowest model available), we see that the side flaps are folded down tightly and joined together in the middle...looking at this, things started to make sense. Joining the flaps under the saddle will resist the bowing of the flaps, and remove the tendency to crease the leather near the rivets.
I really like the feel of this Swift, but recently the saddle has become softer and softer as it "breaks in". I inspected it recently and noticed that while the saddle shows clear impressions from my sit bones, it also is flaring at the sides...especially when I press down at the points where my sit bones have deformed the leather.
This is the reason why I have decided to tie mine. Some may do this for aesthetic reasons (and it does look nice), but I debated with myself at length before I got out the drill and began to scar my beautiful saddle. It took about 5 minutes to do, and here are the results (I still need to trim the lace).
The saddle is now stiff again as it was when new. However, it is also "broken in" so it is still very comfortable. I feel that the lacing gives me more support, and the saddle is now less like a hammock in feel.
Nope, it’s not for everyone. I realize that in doing this I have focused the stress to the points where the laces pierce the leather. Hopefully, the job will last for many years to come. I also believe that had I not done this the "Z" shaped creases that were starting to form in front of the forward most rear rivets would have become more pronounced and the saddle would have lost a critical amount of its structure, and collapsed into a hammock.