After half a life spent on thinking about an alternative to the front wheel suspension I finally started to build.
Why? I don't like dive under braking and I don't like all the stick-slip in the standard forks. The standard tellies aren't very stiff either and they induce great forces on the headstock dictating a very strong and heavy frame. Many reasons to find an alternative and this combined with my non conformistic mindset was enough to take on this challenge. Many, many sketches and drawings decorate my office walls. Virtually all alternative concepts were weighted and compared. From all these I tried to find the simplest system that would solve the issues of the tellies without introducing more misery.
I tried to build something like Bob Horns recumbent racer as shown on thekneeslider.com without much success. Kudos to Bob for getting that to work. I went back to my Steered Top Link (STL) system, maybe I will try it again later.
What is STL? It is a double wishbone suspension where the toplink pivots with the steering motion. It is similar to Norman Hossacks system except for the steered top link. This way it is a bit simpler and it consists of fewer parts.
Credits: I saw a mountainbike with a similar system and started to think, draw, calculate and repeated those steps many times. I searched the web for reference and came across Tony Foales site. He is a man of my taste for all his experiments and hands on creativity. Still no STL, but he gave me some insight in the anti dive effect and other design things. Then I saw a picture of a Diesel car engine powered bike and thought I recognised something like the STL system on that.
From there an amazing quest commenced. Only the name Lajos Kissunn was mentioned by the picture, nothing else. I recognised Lajos as a Hungarian name but Kissunn didn't ring a bell. Google couldn't help me. Fortunately I learned the Hungarian language because we have a summerhouse there. I Knew Kiss was a common Hungarian family name so I tried to google that. Bingo! It led me to a video site in Hungarian where someone filmed a large collection of motorbikes, and yes, at the end of it there was the Diesel bike. In the comments I found a reference to a motor museum in Recsk and it turned out that was just 90 km from our house. A phonecall to the town hall led me to a very friendly campsite owner who had all these bikes on his attic. He showed me the bike and told me the sad news that Lajos Kiss passed away in 2001. Unfortunately, the bike is not running now, and nobody but Lajos ever tried it. Lajos built an Indian styled bike with a Zastava engine too sitting brotherly next to the Diesel bike. All I could do was to take pictures, take some measurements of the bike and admire the Hungarian ingenuity. Built in a shed in a country where not much was available in those days.
I used Toany Foales software to calculate the geometry. The STL concept is not covered by the software but still I was able to find some key measurements from that. At the same time I made a spreadsheet with basic statics calculation to figure out the reaction forces on the frame and suspension parts. All this theoretical stuff gave me a rough idea of how to build the bike. Now I had to make some choices. What engine? Use a bike or build from scratch? Use my Cagiva Gran Canyon?
I hestitated because my cagiva is a very comfy bike for everyday use. Then something nice happened. The donor bike, a suzuki GS1000, was allmost given to me so nothing held me back to cut it in half. At first, the rear end was changed with a monoshock suspension on a braced swing arm. Funny detail: the passenger footrest brackets are now an integral part of the swingarm! At the front it is now a monoshock too. While building, the design changed a bit but still it is the STL system. The datalogger is installed and the first logs are made.
Some changes are made allready, and now it works quite well! It feels like a sportsbike, with quick handling just like I like it. Antidive effect is there, but limited. So it still dives a little which is fine. Further testing is needed, I will write more here as soon as that took place.