explain preload.....too little or too much?
01-30-2010, 06:19 AM
#26
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Re: explain preload.....too little or too much? (Hella_JDM)
You are misinterpreting it. What you have to consider is the amount of spring compression under load, free spring length, and compressed spring length (difference of those first 2 values).
A 35mm (17.5 kg) preload means that you could place 17.5 kg on the spring without the spring moving. But it's still compressed 35mm from its original length. Up the weight to 35kg (add another 17.5) and the spring will compress another 35mm, for a total spring delta of 70mm, so the spring rate is still 0.5 kg/mm. It would be the same if the spring had no preload on it.
This is what Tyson was talking about with the weight of the car on the suspension, preload makes ZERO difference in spring characteristics.
The graph you posted merely moves the force/compression plot to the left. The travel shown for a given force on the preloaded spring plot is relative to the preloaded spring length. Free spring length for a given force will always be the same no matter what the preload is, assuming you're talking about a force higher than the preload (which is always the case on car suspension). If the applied force is less than the preload, then of course the spring doesn't move at all.
A 35mm (17.5 kg) preload means that you could place 17.5 kg on the spring without the spring moving. But it's still compressed 35mm from its original length. Up the weight to 35kg (add another 17.5) and the spring will compress another 35mm, for a total spring delta of 70mm, so the spring rate is still 0.5 kg/mm. It would be the same if the spring had no preload on it.
This is what Tyson was talking about with the weight of the car on the suspension, preload makes ZERO difference in spring characteristics.
The graph you posted merely moves the force/compression plot to the left. The travel shown for a given force on the preloaded spring plot is relative to the preloaded spring length. Free spring length for a given force will always be the same no matter what the preload is, assuming you're talking about a force higher than the preload (which is always the case on car suspension). If the applied force is less than the preload, then of course the spring doesn't move at all.
If the spring is preloaded, the suspension will need more force aplied to it for the damper to travel the same amount.
in my example, (not taking aditional weight sag into consideration), if there is no preload, the suspension (damper) would need a force of 5kg to move 10mm inwards. (i'm talking damper travel here, not spring)
If the spring is preloaded, the suspension would need 22,5kg to move 10mm inwards.
So wouldn't that drive harder?
I understand that spring characteristics are not changed. It's still 0,5kg/mm. But the suspension characteristics do change. It will need more weigt to it to actually start moving. But the spring wil still travel 1mm per 0.5kg.
*Edit* Come to think of it, you are correct if taking sag into consideration.
Lets say our vehicle puts a 17,5kg weigt on the spring, it will compress 35mm.
So in the above diagram, the nullpoint is shifted to the right (instead of to the left if preloaded).
So for the damper to travel 10mm (past 35mm, our new nullpoint) it will need +22,5kg.
So it will need the same amont of force (weight) to start moving.
But the tarvel of the damper is compromised, so there is a chance it will bottom out.
Whereas with preload, there is not. As it will not travel under the static weight of the vehicle.
btw, I like your avatar. Just got the M.A.S.K boxset myself :p
Last edited by Pandor; 01-30-2010 at 07:01 AM.
01-30-2010, 08:01 AM
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Re: explain preload.....too little or too much?
Boxset?? They have it on DVD?? Do want!
Anyway what you say is physically true for those conditions but doesn't really happen like that in the real world. Most cars place a static weight of anywhere from 400 to over 1100 lbs. On the spring at each corner. You'll never get that much preloaded on the suspension of an actual car. If you did, the car would act like it had solid suspension until the preloaded amount is surpassed. If that were the case, the car would be damn near undrivable, and traction would be a major issue.
Anyway what you say is physically true for those conditions but doesn't really happen like that in the real world. Most cars place a static weight of anywhere from 400 to over 1100 lbs. On the spring at each corner. You'll never get that much preloaded on the suspension of an actual car. If you did, the car would act like it had solid suspension until the preloaded amount is surpassed. If that were the case, the car would be damn near undrivable, and traction would be a major issue.
01-30-2010, 11:11 AM
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Re: explain preload.....too little or too much?
*offtopic*
Yup, madman released the complete series in 1 boxset. (8) Region 4 DVDs (aus. release).
Vortex Pictures also did, but I don't think that one's official.
Currently catching up with 80's toons (he-man, M.A.S.K., dino riders, gi-joe,..) :p
*ontopic*
Yeah, figured that much.
I''ve just installed some k-sport coilovers, and that got me picking my mind.
All clear now.
Yup, madman released the complete series in 1 boxset. (8) Region 4 DVDs (aus. release).
Vortex Pictures also did, but I don't think that one's official.
Currently catching up with 80's toons (he-man, M.A.S.K., dino riders, gi-joe,..) :p
*ontopic*
Yeah, figured that much.
I''ve just installed some k-sport coilovers, and that got me picking my mind.
All clear now.
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