TLDR: Can I find the softest spring by: height remaining after preload, at full shock compression = spring solid height? 16" extended shock with 12" 150lb/in spring under 715lbm static load compresses 4.75" to 11"; add 3.6" preload to get to ride height of 14.7". At full compression, there's about 7.5" available spring height on the shock. 7.5" available minus 3.6" preload = 3.9" for spring at full compression, very close to 3.5" solid height = good utilization?
I mentioned in my intro that I'm coming from off-road trucks, where maximum travel and soft springs are required.
I'm now working on a reverse trike, and solved for optimal shock travel by unladen ground clearance to ensure easy servicing -- my trolley jack minimum is 5". I'm now moving on to spring selection.
To re-cap, I ended up with a bit too much bump:droop ratio, which could be improved when laden with soft springs (more compression = less bump/more droop). In addition, the trike is obviously roll-happy, and so maximizing the decrease in CG with passenger mass via soft spring deflection is desirable. Finally, greater travel with soft springs gives increased grip.
It seems there are a number of common methods to select spring rate:
- Copy from aftermarket kits or forum posts: unreliable, especially with a new & (technically) unpopular platform
- Solve for spring rate with zero preload at ride height (the Hyperco calculator)
- Solve for suspension frequency: given the wide range of acceptable results, I'm unclear if/why specific suspension frequency would be prioritized in suspension design
Why not solve for minimum spring rate? Probably because it would maximize unladen to laden ride height change, which is usually harmful, as it would negatively impact ground clearance and aero. With a heavy load and/or short travel, the car would be riding on the bump stops.
But in this specific application, since the trike isn't aero to begin with, I want to maximize that laden ride height reduction to lower CG to reduce load transfer. My passenger load is fixed; I don't have to worry about varying cargo load. And I have 3.7" of available compression travel in the shock to avoid the stops.
To best use a minimum spring rate, I would have to use the entire load available from the spring, just over solid height (coil bind). That is, the spring would almost go solid, or coil bind, exactly at full shock compression. So if I know total available spring height on the shock at full compression, could I subtract the actual preload height required (3.5") and the solid spring height (3.5") to give the free height remaining at full shock compression? It seems this clearance should be as close to zero as practical. Alternately, optimal spring rate is where height remaining after preload, at full shock compression = spring solid height?
But here is a result:
Is this accurate?
What is an appropriate shock compression or wheel bump load capacity?
