Progressive suspension in any format is worth the change vs linear. Thats why manufacturers of modern bikes put in link mechanisms in rear suspension, progressive damping in top of the line shocks etc. Its all about making the action of the suspension progressive. Ideally suspension should be soft and supple to absorb bumps in the road, riding over gutters etc, but if it is soft and linear then you run the risk of bottoming out when you have a big hit or jump - you want the suspension to be supple for small movements, but you do NOT want it to be soft and supple for major suspension movements. Progressive suspension is a way to deal with that juggling act.

So a change to progressive fork springs will help. Hyperpro are the leading brand of progressive springs for bikes in the world.

But bear in mind, in your case, the weight of your pillion and luggage will make little different to your forks (front end). At least 95% of that additional 100 kgs or so of weight will go through to the rear suspension, and that is the priority for you to take care of.

I recommend you talk with a guy I know who is one of the leading Hyperpro technicians in Holland who also happens to be an R80 (airheads in general) enthusiast, and a former BMW dealer head mechanic. He has 12 airheads, some as dirt / trials bikes, some as off road touring bikes, some as highway touring bikes, some as round town bikes, some as choppers and some as sidecars. All have modified suspension at the back, many have different forks at the front, but some have modified versions of BMWs OEM forks. He is probably one of the best guys in the world to talk to regarding airhead suspension in general, and definitely the best guy you could possibly talk to about airhead suspension as it applies to adventure touring.

Call Bas on +31 172 417171 during office hours.

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Don't expect too much from the upgrade. I have progressive springs at the front and Ohlins at the rear on an R100GS PD. It's still extremely primitive. I did also have thicker oil in the forks, but that didn't seem to make any difference. Have since been advised not to do that, as it's not so good for the seals. The Ohlins helps a little, but I still make sure I don't overload the back with weight (i'm a bit heavy anyway).

To put it into perspective, I travel with a friend who has an R1100GS with the paralever. He is able to ride tight twisty roads much faster than me. Where the R100 is diving, drifting wide and becoming unstable, he is able to go fast, using the brakes in the corners.

More important has been fork maintenance. Have an expert do it and make sure everything is tight as specified, that makes a big difference to stability. I don't get the bars wobbling and threatening a tank slapper anymore.

In reality that doesn't put anything into perspective as the bikes are chalk & cheese in the handling department.
You shouldn't be able to keep up with him (if he's a competent rider), him being on a telelever bike, especially where braking & corners are concerned as they excel at that.

While I totally agree with your main point, it's the 1100GS that has both the telelever and paralever suspension, fore and aft.

https://www.google.co.uk/search?q=pa...w=1330&bih=602

The 100GS has just the paralever, last time I looked:-
https://www.google.co.uk/search?q=r1...w=1330&bih=602

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Dave