|650ss Forks by Ed Milich
A lot of complaints have been registered over the years about the “spindly” Allazurra forks. Quite the contrary, I‘ve gotten mine to work quite well, both on the street and racetrack! 650ss forks are essentially a smaller (35mm) version of the Marzocchi Strada forks that are highly sought after upgrade for Moto Guzzis and other European cycles. I actually perfer the Ally OEM forks (albeit modified ones) on one of my race-winning Alazzurras. I’ve ridden Allys with older 38mm Marzocchi forks from bevel drive Ducs grafted on and I was not impressed. The older designs are even clunkier than the stock Allazurra fork design, as they use a damper rod along with a ball check valve that looks more at home in a toilet than a sporting bike!
The 35 mm Ally forks have a very simple damper rod arrangement. Compression and rebound damping are controlled by the size of the orifices in the damper rod where the oil pass through. These forks also feature an anti-friction bushing at the bottom of the fork tube, which is a welcome feature.
Stock Allazurra fork springs have a spring rate of 0.45 kg/mm, OD of 28.5mm and a free length of 480mm. In comparison, the springs that I use for racing applications are Progressive 11-1107 with a progressive 0.63/0.89 kg/mm rate. This is between 50%-100 higher than the stock rate! With the stock springs, my front end was chattering around the constant radius turn 1 at Willow Springs. Wheel chatter is bad news at 70 MPH, lemme tell ya. The progressive nature of these aftermarket springs is not that essential to me. At Willow Springs, I only use about 2” of fork travel anyway, so I’m not utilizing the full range of the progressive spring anyway. What is nice about the Progressive springs is the organization of their catalog and their wide availability. Note that these springs are an inch shorter than stock. I make up the difference in heights with Racetech gold valves and a custom gold valve mount. You can also make aluminum or plastic spacers to preload springs and make up the free length difference depending on your weight and the springs that you use.
I also installed the Racetech gold valves on my bike. This alone is not an effective modification. Rather, the Gold Valves introduce another tuning variable by allowing you to separately tune the compression and rebound damping of the fork. With Gold Valves installed, you can change the compression damping by changing the preload of the spring on the gold valve. You can similarly change rebound by changing the fork oil viscosity. Stock Alazzurra fork oil spec is 150cc per leg. I used SAE 7 weight oil in my forks, and filled them 150mm from the top with the fork springs removed. This setup seemed to work well. Note that gold valve installation is a one way street, as you have to drill out your damper rods upon installation. There’s no going back to stock without a severe loss of compression damping after that.
On this racebike, I have the forks dropped down about 1” in the triples. This allowed me to decrease rake trail to close to 28 deg/110 mm. I had to make ~1” handlebar risers to put under the stock bar mounts so that I could drop the bars. Otherwise, the top of the fork tubes will hit the bars.
The only place I ever see the limitations of the stock forks is on high speed hard braking areas such as Daytona’s turn 1 where the 35mm forks can be seen to flex. It’s not that big a deal to me, so I just kept my forks stock in diameter. Larger diameter forks tubes would surely decrease this flex.