Ok let's face it the 83 K100 is a bit of a rocking horse. Comfy and predictable which is nice. But can I stiffen my front end... (Ooo er missus) without compromising the plush ride. Progressive springs, thicker oil or just a service of the existing bits.

My '89 K100 with "S" forks which are supposed to be stiff has a pair of the progressive springs with the tighter coiled bits at both ends from Motorworks in them and it's as soft and wallowy as owt, not recommended. It is possible though that more oil should now be put in, shame they don't come with any instructions! I put 300ml into each fork and the air gap is now 265mm, which is friggin' enormous.

People seem to highly recommend an oil change in these Sachs forks if they're not working properly for you, though stick to 5-10w. If it's too soft stick some more oil in. I have not yet had a chance to test mine with new oil in though, it's been to many bits having new fuel hose put on instead. I've also shoved in about a centimetres worth of washers in each fork, hopefully that'll help a bit too. Old tricks but it's old tech!

Thicker oil will compromise the ride as it increases the damping, It will slow the dive but not stop the dive.

Good fork springs will make it better, I prefer single rate at the correct rate for your weight over progressives which are always a compromise.  If you do go for progressive, look for a true progressive spring that increase the rate continually as the spring compresses, not just a progressive with a soft rate and a hard rate. The soft rate squashes up, then the hard comes into play.

To reduce the dive, more oil of the same rate works by reducing the air gap over the oil.  In an RT I used to use 400ml instead of the recommended 360.  It was recommended to me by a BMW mechanic that worked on the police bikes of the time, many of the police riders didnt like the dive either.

Al

You can also install dual rate springs. (What I will put on my K75 in the very near future.)

From the Works performance site:

Kits for street bikes, feature a soft initial rate that "crosses over" to a stiffer final rate. This allows a comfortable "cruising" rate in the first part of the suspension movement, but stiffens for big bumps and to resist front-end dive under braking.