Preload confusion

My discussion surrounds the effects of initial preload and ride height. If you are at max damper extension and you put a preload then you are still able to raise ride height. But from video it is also saying that the load on spring from vehicle is going to result in the same amount of compression distance as a result of spring rate. The only thing I can assume is that either the damper is still somehow extending upwards even further so that the new baseline compression is at a greater height or that the spring due to the preload causes the compression distance to decrease which effectively means I have a stiffer spring rate which contradicts the video. Help would be appreciated on understanding what's going on.

If a suspension is preloaded, you should have another mechanism to adjust the ride height, such as an adjustable push-rod. If you move the spring perch to change the ride height you are actually changing the pre-load amount. Without another adjustment you will not be able to raise the ride height beyond the point were you have preloaded the spring with the effective corner weight

That's where Im confused, the video on the subject of springs state that putting preload on your linear spring does in fact have the ability to raise your car. But I'm having trouble understanding why this is happening. To understand you correctly you're saying if the corner of that car weighs 500 lbs and I preload the spring 500 lbs then that will result in the car's ride height not going up any further correct?

That is correct, assuming the motion ratio (spring motion relative to suspension motion) was 1.0.

There is something amiss because (putting numbers to create scenario) if the linear spring rate value were to be 250 lb/in, preload would have compressed our spring 2 inches and based off the lesson, then after putting the car's 500 lb weight down it would still have compressed the spring 2 more inches totalling 1000lbs of force and 4 inches of compression. What am I not seeing here?

The corner weight up to the preload amount does not compress the spring any additional amount at all. So if you had a 250 lb/in spring preloaded 2" (500 lbs of preload), and you had 500 lbs of force, the amount of force on the spring would still be 500 lbs, so the spring would not have moved at all, if the corner weight were 750 lbs, the spring would compress another 1" (3" total or 750lb).

I'm sorry I have not watched the lesson -- I have used pre-load on purpose built race cars for almost 30 years. We use it with droop limiting to prevent the ride height of aero cars from increasing (and thus losing downforce) with weight transfer.

Fred, you're over thinking it.

The spring compresses a specific amount from a force applied to it, it doesn't matter how that force is applied, whether by pre-load or the vehicles weight.

In your example, there is a 500lb force on the spring, applied by the preload, and the spring is being held at a compressed length. In order to compress the spring further there needs to be a force greater than 500lbs. Here the vehicle is applying a nominal force of 500lbs, which may be what's confusing you - let's say the vehicle weight was 499lbs, this is less than the 500lbs of preload, so it isn't enough to REPLACE, NOT ADD TO, the preload. However, if the vehicle weight was 501lbs, that's more than the 500lbs pre-load, and it will take over the load on the spring from the pre-load and compress it slightly from the pre-load position.

Hey guys, yeah I finally understood it, the beginning bit of David's last post initiated it and Gord, your post solidified the understanding, thanks!