Quote:
Originally Posted by Jhill
I'm not sure I follow you in this. The stroke will always be a ratio of droop vs travel...(There are two different stroke measurements which do not always overlap - primary spring stroke, and damper stroke, thus the reason for a secondary spring to match the damper stroke.
...Given same example is 30% sag with 11k spring and zero preload what do you think your sag / - travel will be at 16k rates? - It would be dependent on the weight at the installed spring length***
Obviously less and there goes your traction over humps and inside tire lift (A FACTOR OF IMPROPERLY MATCHED ASB IN RELATION TO LOAD)which is where the helper / tender spring comes in to gain - / droop travel back < not necessarily.
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Note -
You can't have sag without preload...unless you are talking about something else...
I think your examples further establishes my vague point. Droop is a portion of the total damper travel, where as it ISN'T relevant to the total spring length. Sag is however a factor used for springs, not dampers. Thus my point on why these two things need to be matched dependent on weight and length. Using a tender or helper spring ensures there is still some load on a spring at full droop. You are inevitably going to have some preload on the spring in order to measure sag. The differences would be where in the damper stroke the spring starts to compress.
I didn't include an example for it to make sense previously. But in a situation where you have a damper that has 8 inches of extension at full droop, but your spring is only 6 inches long, you have a situation where there is no load on the main spring when it goes passed 6 inches of droop, this would be zero preload. In reality like you said, normal road cars won't see this level of extension during driving where as a extreme off-road truck can work well passed 8 inches of droop from static ride height, but in any case you never want your spring fully extended before the damper fully extends.
Adding a tender/helper or even a secondary main spring is what needs to be done, with your example of off-road vehicles, they are going the route of a secondary rate spring> and then a helper spring if needed. In the case where a spring rate is significantly stiffer than the total load on said wheel, the spring does not need to be long or longer than the damper stroke length, but in such case the damper travel is still based off the factory length and available perch length. The complexity of tenders comes from trying to match weights when the damper is extended farther than the spring and trying to manage compression difference's. This is a completely different discussion though.
