jpmobius said:
An easy way to see if you are in the ballpark is to measure the full travel of the shock with the spring removed. It need to be quite close to the travel you expect to see in your own set up.
For the record, I have taken the spring off and measured the total travel of the shock. The travel does suffice for my design.
I understand what you are saying, essentially it is the total clockwise movement equals total anti-clockwise movement, principles of moment. The anti-clockwise force in this case is the force of the spring, which due to the nature of the spring actually creates a variable force which increases as the lever (crank) rotates, i.e. the spring force in N/mm, which is a compound force from zero to full compression.
The amount of compression of the spring as the lever rotates through its arc varies due to the spring being a linear movement versus the rotational movement of the lever in relation to the top mounting point of the spring.
I agree with your observations, however what needs to be remembered are that as the lever moves through its arc, the spring will be compressed. The compression of the spring will be accumulative (compound) as it shortens, which means the force will increase through the arc of the lever. However as you have explained, as the lever moves through its arc towards the extreme of its range, the linear movement (that which compresses the spring) becomes less than when at the 90 degree point. But as it is still compressing the spring, a greater force will still be needed than when in the first range of movement before the 90 degree point. Essentially it means the suspension will feel soft moving to firm and then slightly softening but not enough to be an issue.
As for the actual damping of the shock unit, this I completely understand, I am familiar with how shock absorber/dampers work.
What needs to be remembered is that how the bike will be used and considering Kawasaki had these characteristics on their 2004 ZX10R which most road riders never noticed, I'm confident that my project will be fine, especially as it will struggle to get over 90mph.