Stiffer fork springs to hold up a heavy fairing
- Thread starter jimbo
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o0norton0o
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Racetech has fork springs for commando. They are $150. for the front pair. They are 23.5mm OD which fits down the stock fork tubes and 410mm long. The stock springs are 460mm long, so you have to make up the 50mm with a spacer. (I make my spacers out of delrin and use a thick metal washer at both ends) I've been experimenting with custom dampers for a few years. From all the testing and research I've done, I think the racetech spring rates are a little stiffer than they claim, and they come in 5kg/mm increments, so you can't actually get a .67kg/mm spring to match the stock spring of a commando. To get right to the point, you should get either .75kg/mm or .80kg/mm. (Peter Verdone agrees with me on this. His website has some great information)
On my first prototype set, I bought the 80kg/mm springs, even though racetech's online calculator said the calculated spring suggestion for my weight was .93kg/mm. I thought that was a crazy stiffness for a road bike. (maybe not for a race bike), so I chose a spring between the stock .67 and .93kg and bought the .80kg/mm spring. In the couple years of testing, I've tested many different springs. The ,80kg/mm was only a little on the stiff side, but had a very quick feel to the suspension which gave a lot of confidence to the handling with Avon RR's inflated to 32-34 respectively. If I was always aggressively sport riding, I would use the ,80kg/mm springs without complaint...
With later suspension builds, I decided to experiment and go for lighter springs and use thicker fork fluid to get an idea what those changes produced in terms of handling feel. Right now I have .62kg/mm springs (not from racetech) in my forks and increased the thickness of my fork fluid from 2.5wt to 7.5wt to see if I liked it. It works OK, and is a very soft riding set up, but noticeably less confidence inspiring when cornering fast because the spring softness translates as a looser feel... There's a chart in the "racetech suspension bible" that says the actual best feel and best traction and do not peak at the same point.... (interesting probably only to me) but I'm playing around with that....
Anyway,.... here's the chart below of springs that fit a norton commando: FRSP S2341080 is on my first prototype dampers (btw the damper cartridge in my bike is not a stock norton damper. It's a modern cartridge modified to fit commandos) The spring choice determines 90% of the character of your suspension, the damping is just a spring modifier. Getting the spring right for your intended use is most important. (IE racing, mixed sport riding, touring) By those terms I mean: best handling, good handling but softer, and softest and most comfortable ride. You definitely have to be careful and not go too soft or you'll bottom out (probably obvious...)
I'm 225lbs, have a fairing on my bike, and I do have some weight on my hands because my bars are shorties, even though my interstate tank pushes my mass backward further than a roadster tank would, so my .80kg/mm springs are probably a good choice or maybe .75kg/mm if you want a softer ride. Depending on how heavy your fairing is and how heavy you are maybe .85kg/mm, but .80kg/mm felt stiff to me....
.... But what the fuck do I know... there's really very few suspension experts around to pick their brains. Racetech's Suspension Bible is probably the best source of information that I've found.
On my first prototype set, I bought the 80kg/mm springs, even though racetech's online calculator said the calculated spring suggestion for my weight was .93kg/mm. I thought that was a crazy stiffness for a road bike. (maybe not for a race bike), so I chose a spring between the stock .67 and .93kg and bought the .80kg/mm spring. In the couple years of testing, I've tested many different springs. The ,80kg/mm was only a little on the stiff side, but had a very quick feel to the suspension which gave a lot of confidence to the handling with Avon RR's inflated to 32-34 respectively. If I was always aggressively sport riding, I would use the ,80kg/mm springs without complaint...
With later suspension builds, I decided to experiment and go for lighter springs and use thicker fork fluid to get an idea what those changes produced in terms of handling feel. Right now I have .62kg/mm springs (not from racetech) in my forks and increased the thickness of my fork fluid from 2.5wt to 7.5wt to see if I liked it. It works OK, and is a very soft riding set up, but noticeably less confidence inspiring when cornering fast because the spring softness translates as a looser feel... There's a chart in the "racetech suspension bible" that says the actual best feel and best traction and do not peak at the same point.... (interesting probably only to me) but I'm playing around with that....
Anyway,.... here's the chart below of springs that fit a norton commando: FRSP S2341080 is on my first prototype dampers (btw the damper cartridge in my bike is not a stock norton damper. It's a modern cartridge modified to fit commandos) The spring choice determines 90% of the character of your suspension, the damping is just a spring modifier. Getting the spring right for your intended use is most important. (IE racing, mixed sport riding, touring) By those terms I mean: best handling, good handling but softer, and softest and most comfortable ride. You definitely have to be careful and not go too soft or you'll bottom out (probably obvious...)
I'm 225lbs, have a fairing on my bike, and I do have some weight on my hands because my bars are shorties, even though my interstate tank pushes my mass backward further than a roadster tank would, so my .80kg/mm springs are probably a good choice or maybe .75kg/mm if you want a softer ride. Depending on how heavy your fairing is and how heavy you are maybe .85kg/mm, but .80kg/mm felt stiff to me....
.... But what the fuck do I know... there's really very few suspension experts around to pick their brains. Racetech's Suspension Bible is probably the best source of information that I've found.
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