Quote:
Originally Posted by Jhill
I think we mean the same thing but using different wording. However not having sag without preload? Never heard this before...
If I drop a spring rate I will need to add preload to it to maintain this 30% sag and if I increase my rate I will have to add a helper/tender spring to maintain this sag otherwise I'm losing sag which equals a lose of droop (negative) travel. - you don't need a predetermined amount spring sag...if you reduce rate yes it will increase compression, everything else being equal, but it also changes other things.
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I think i understand what you are getting at, but using sag as a nominal point of reference isn't the correct way of determining anything without factoring preload. It's relevance is to the rated amount of compression (spring rate/weight) vs how much force is actually applied. In your example, 30% spring sag may or may not be acceptable depending on the amount of preload and the total length and weight. But it's not accurate or relevant if you haven't set preload. Thus what i meant by not having sag without preload. If what you are measuring is 30% spring compression with no preload, you are measuring the static weight divided by the spring rate, while also taking into consideration the motion ratio and angle correction). There is no point to making hypothetical changes. If you match your springs to have 50% bump travel with little to no preload and still fall within a safe limit of stroke before fouling anywhere, you've already accounted for sag. Whether or not the spring continues to sag overtime is a different discussion.
In any case not setting any preload means there is a point within the damper travel where a spring isn't engaged. Simply tightening it down to the lowest point of engagement is still adding preload, regardless if it's a significant amount of force or not. Spring sag can only then be determined once the spring is loaded, without preload you are measuring the percentage of load capacity used. This is not the same as sag.
I'm not sure spring sag is even a good reference for cars anyways. We are dealing with weights far greater than with motorcycles where the rider weight is a significant factor on overall load. Unlike with a car, where driver weight is only a small percentage and usually less than the standard amount of preload that should be applied.
With cars, the manufacturers usually account for driver weight by counter weighting the car and setting preload. With bikes the sag is generally countered with 1/2 - 1.25 inches of preload.
We'll need to start a new thread for this topic lol
