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:Dhey guys i have dropped the rear of my bug but i was wondering if i have to notch the springplates ? it is very low and i have removed the bumpstops but it seems to be very bouncy now? just ordered some new short rear shocks because i thought they might be bottoming out ? i can get pics if that helps thankyou jamie:D
 

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When you lower the rear there is no preloading on the torsion springs making the ride sloppy, which is what i guess you're feeling. Get some gas shocks and that will stiffen it all up a bit.
If your spring plate starts to hit the frame you get a banging as metal hits metal and you'll know about it! on a late model you can grind a part of the frame out of the way and notch fairly shallow on the spring plate to stop this. (only needed if you go heavily low, 3 spline-ish)
 

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Might be worth noting Jammee, I was told it would fail the MOT if the bumpstops were removed, you're supposed to cut them down instead.
Any ideas if this is right?

The bug in your avatar looks awesome!
 

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you've been told a fib there mate. i've never run bumpstops, you can't get a car anywhere near low with them still on, even cutting them down is pointless once you go passed 3-4 inches.

jammee, i'd say you weren't 3 splines if you haven't notched your plates, your car would have about 2-3 cm of travel before bottoming out. the first time i went 3 splines i drove round the block and the spring plates were almost constantly hitting the frame. Nothing a little grinding couldn't sort out though!
 

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Because the weight of the car is the preload. Preload the torsion bar prior to weight would cause the torsion to not bounce up and down maybe..
 

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The spring plate is pretensioned on the lip below it on the chassis. This means there is torsional stress induced in the spring before any weight is put on it, once the spring needs to act, it does with a 'stiffer' spring rate.

When lowering the car by rotating the spring plate around the splines on the end of the torsion bar, the lip stays in the same place and the spring plate moves up, this means there is no way to put any load into the spring. The sloppy ride is due to the torsion bar twisting more easily from rest.
 

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You ca also use thicker torsion bars like a lot of us offroaders do! ;)

IF you notch you springplates, for God's sake do NOT leave ANY sharp corners in the notch, cos you'll crack your plates.
 

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The spring plate is pretensioned on the lip below it on the chassis. This means there is torsional stress induced in the spring before any weight is put on it, once the spring needs to act, it does with a 'stiffer' spring rate.

When lowering the car by rotating the spring plate around the splines on the end of the torsion bar, the lip stays in the same place and the spring plate moves up, this means there is no way to put any load into the spring. The sloppy ride is due to the torsion bar twisting more easily from rest.
so the torsion bars are not linearly elastic? i.e. force require to turn 2 degrees is double the force required to turn 1 degree? I disagree, (negating minimal effect of "sagging" and imperfections) unless there is some serious metallurgy going on in those bars I dont know about.

if you discount the effect of the twisting spring plates, while the suspension is "preloaded" surely the torsion seen by the torsion bars at rest (not resting on bump stops or bottom stops) is the same regardless of ride height?

taking the plates into account, a stock car sees little twist of the spring plates, except at really large travel. this means the spring rate is almost all due to the torsion bars. however in a lowered car, the spring plates are twisted at rest, giving a stiffer ride, however, notching spring plates will reduce their torsional stiffness resulting in a softer overall spring rate than a car at the same position with full plate
 

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Yes but you haven't factored in travel. 3" travel vs 8" travel means a stiffer ride for the 8". Preloading is only really a factor with raised cars. We preload our bars and then at braces to stop the resultant force kicking the springplate past the end stop. The plate is STILL on the stop with te weight of the car on the ground. Snapped torsion bars happen sometimes! :D
 

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Preloading is only really a factor with raised cars. We preload our bars and then at braces to stop the resultant force kicking the springplate past the end stop. The plate is STILL on the stop with te weight of the car on the ground. Snapped torsion bars happen sometimes! :D
yea that makes sense, although you are only increasing the spring rate when the plates are on their bottom stops, I dont even want to think about the forces involved in snapping a torsion bar!

but you haven't factored in travel. 3" travel vs 8" travel means a stiffer ride for the 8".
I still dissagree, surely the first 3" of travel on the 3" car would be stiffer than the first 3" of travel on the stock car?

after that, say the 3, 1/2th inch, when the 3" car is squashing the bumpstop or bottoming out, the stiffness is huge, effectively feeling like you are running rocks for springs, while the stock car is gradually getting stiffer, but certainly no where near as stiff as the bottoming out car
 

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its not very complicated, imagine a strut suspension car, if you bounce on the spring, its damn soft, if you then put a ton of weight on the car and zip tied the springs up higher than usual (for arguments sake) the spring is going to become stiffer.

Springs do not have linear properties. otherwise they'd just keep going and the car would hit the road. if you remove the axle from the spring plate and try to push it upwards, it's very difficult. pop the spring plate over the lip (removing the pretension) and that first inch of movement becomes very easy.(you can do it with a finger or two).

The back of a volkswagen is preloaded to give a responsive ride.

Removing the preload (lowering) you get sloppy springs until you bottom out.

johnser, have you ever riden in a lowered beetle? Front gets stiffer, back gets sloppy.
 

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Springs do not have linear properties.
torsion bars do (again, negating the effects of creep "sagging" and imperfections)

otherwise they'd just keep going and the car would hit the road.
no, a linear spring by definition obeys Hooke's law, which states that the force with which the spring pushes back is linearly proportional to the distance from its equilibrium length (the same is applies with torsional springs, except with torques and angles instead of forces and distances)

the car would never bottom out unless it either reached the limit of its travel, or the elastic limit of the spring.

imagine a strut suspension car, if you bounce on the spring, its damn soft, if you then put a ton of weight on the car and zip tied the springs up higher than usual (for arguments sake) the spring is going to become stiffer.
the mass on a linear spring does not affect its stiffness, what you describe here is the property of some non linear springs that become stiffer as they are compressed more (most strut sus. car springs). Therefore, by compressing them more than their stock height, you do increase the stiffness, this is the property I am trying to get across about the spring plate and torsion bar combination, which gives a similar nonlinearity - therefore, by lowering, you increase the stiffness.

if you remove the axle from the spring plate and try to push it upwards, it's very difficult. pop the spring plate over the lip (removing the pretension) and that first inch of movement becomes very easy.(you can do it with a finger or two).
while what you describe is obviously true, you are not affecting the stiffness, put the car on the ground and (again negating the effect of spring plates and camber) as long as its not resting on the bottom stops, to push it down an inch will take the same force. including the effects of the spring plates and the lower car will actually take MORE force to push down an inch. (I've explained why before)

The back of a volkswagen is preloaded to give a responsive ride.
the back of a volkswagen is preloaded to give the correct (stock) ride height without having massive positive camber when the car is jacked up

johnser, have you ever riden in a lowered beetle? Front gets stiffer, back gets sloppy.
no, which is probably where the problem is; as I am looking at this from a purely mechanical point of view. the ride is "sloppier" as we instinctively view the suspension travel as a whole rather than inch for inch as I have been doing here. so the car with the 3" travel is stiffer in the 3"s of travel it has, compared with the first 3" of travel in a stock car, but in the stock car, 3" is only a fraction of the full travel.

I've tried to explain to the best of my ability and knowledge.
 

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"no, which is probably where the problem is; as I am looking at this from a purely mechanical point of view. the ride is "sloppier" as we instinctively view the suspension travel as a whole rather than inch for inch as I have been doing here. so the car with the 3" travel is stiffer in the 3"s of travel it has, compared with the first 3" of travel in a stock car, but in the stock car, 3" is only a fraction of the full travel."

i think we're arguing different points here.

Yes springs obey hooke's law but only until they reach an elastic limit. i believe the preload is to bring the neutral position of the spring closer to it's elastic limit and therefore let it stiffen up before the car grounds out at stock height.

So, by relocating the spring plate further round the torsion bar, the neutral position is now higher and therefore needs even more travel to reach the elastic limit. A lowered car will never get stiff, just hit the ground.

Here's what i'm trying to explain: -


I know it sounds odd that a lowered car isn't stifferthan a stock one but this is how i see it after driving them and experiencing the differences. I could be wrong about this explanation but i know for a fact a lowered car is not stiffer than a stock car in both of their first 3" of travel.
 

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while that graph is correct, (assuming the x axis is torsional strain and the y axis is torsional stress) if the springs were loaded past their elastic limit they would deform - i.e. not spring back as far. that graph actually suggests as they reach their elastic limit, they take less stress to continue straining, yielding plastically, they do not become stiffer (ignoring the effects of work hardening).

this can be replicated easily, get a small spring you can easily stretch and pull it, there comes a point where it takes little extra effort to extend it further, this is the curved over region of your graph - when you let the ends go, it will not go back to its original shape - it has plastically deformed

neither a lowered or stock car is likely to be anywhere near this region. the only exception being severely raised and hammered off-roaders, as suggested. even then, I bet defects and fatigue cycling, coupled with the hardness of the materials make any plastic deformation prior to ultimate failure hardly noticeable.

I'm willing to accept, if thats the general consensus that lowered rears feel "softer", but I cant for the life of me find anything that suggests they should. even the geometry of the arcing axle tubes and spring plates only serves to increase the stiffness of lowered cars. It is puzzling me...
 
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