Torsion Bar Stiffen When Lowered?

[theecho]

Hey All..

Just wondering, if i get the torsion bar lowered (around 50mm) will the rear suspesion stiffen up?

Reason i ask is i carry rear passengers most night, as standard the suspension drops i would say around -50! So i want to be sure if i lower it wont then drop another silly amount when i have rear passengers so its riding on the bump stops etc and bottoms out going over a stone! :P

Cheers All! :y:

[liam7200]

i dont now mate but mines be lowerd 60mm at back n mines alway full when goin to cruises n it fine catches on bumps but does that when it just me i would drop it bout 40mm iv u want less scrapping

hpe that helps a bit :P

[GroomGTI]

lol i have mine dropped 90mm its still fine with some one in the back. catches on the odd speed bump nothing major. You will have no problem.

[KamRacing]

Hey All..

Just wondering, if i get the torsion bar lowered (around 50mm) will the rear suspesion stiffen up?

Reason i ask is i carry rear passengers most night, as standard the suspension drops i would say around -50! So i want to be sure if i lower it wont then drop another silly amount when i have rear passengers so its riding on the bump stops etc and bottoms out going over a stone! :P

Cheers All! :y:

no it wont stiffen up at all. Its just lower :d

[Mochachino]

my mates is lowered about 45 and with 3 poeple on the back seat it JUST starts to catch on the arch when he goes overa big bump.

but it dosent stiffen up at all.

[VTSLeics84]

ive had 6 ppl in mine and mine dont catch at all on standard vts rims :s

[Modified]

6 people!!! lol one in the boot?

[Toad]

It will actually do the opposite. I've set my rear dampers to ther stiffest setting, and the rear is still very floppy. Bigger torsion bars are the way forward.

[KamRacing]

having the dampers too stiff vs the spring rate can just make the car skittish. I use the lowest setting I can on adjustable dampers. Does require a bit of experimentation to get it right though

[Toad]

Yes. Unfortunately for me, it's the lesser of 2 evils though. Before I stiffened them up, I could push the rear down with one finger. It's a bit better now, but not great... :(

[williamsvts]

it doesnt get softer. it just stays the say. to change the rear spring rate you would need to change the torsion bars.

[Toad]

If the trailling arms are sitting at different angles as a result of the altered ride height, then it would make a difference in theory.

[williamsvts]

you remove the whole bar when lowering it though. its not as though you are tensioning/untension the bar when lowering it.
when your car is in the air its under no tension, thenthe spring rate of the bar determines how low it sits when you drop it down.
if your saying it gets softer, then if you were lowering it 40mm, you would only need to lower it 35mm and the softer rate would make it sit lower. know what im saying? but you lower it by how much lower you want it to go.

[Toad]

Yes I understand mate. When you want to set your desired ride height, you simply remove the torsion bar, set the trailling arms, and pop the bar back in... However, my point is to do with the angle of the arms rather than the torsion bar itself. When you lower the car, you alter the angle that the arms sit at, so this could then alter the amount of movement they make when under the same amount of stress. Do you see what I mean here? Purely as an example... The new ride height might mean that if you add 100kg to the rear, it moves the rear end down 25mm, but the same 100kg might only move the non-lowered car down by 20mm.

Think of it like a clock, where the clock is the torsion bar / axle, and one of the hands is the trailling arm. Right, if the hand is pointing to 5 o'clock, and you apply a certain amount of force down on the car, so much so that the trailling arm is now pointing to 4 o'clock due to the amount of coil the torsion bar has made. Are you with me? Now imagine that you have altered the ride height of the same car, so the hand is now pointing at 3 o'clock as standard, instead of 5 o'clock. Add the same amount of force downward, which moves the hand to 2 o'clock, as the torsion bar has coiled the same amount. Right, in both instances, the torsion bar has allowed the same degrees of rotation, I.E, 1 hour in this example. However, look at the difference in the vertical height of the hand! When it moved from 5 to 4 o'clock, the hand didn't move upwards very much in comparison from when it moved from 3 o'clock to 2 o'clock.

I know it's not a good example, but do see where I'm coming from?

[williamsvts]

trailing arm is still the same length should should act any differently.

[AdamWhy]

i think you can make it stiffer....not sure tho...

[williamsvts]

you cant, unless you get thicker bars.

[Toad]

trailing arm is still the same length should should act any differently.

Read it again... It's nothing to do with the length of the trailling arm. It's the angle that the arm currently sits, compared to how it would sit if the car was lowered. When the trailling arm is horizontal or close to horizontal, there will be more vertical movement made to the car than with the same force applied to it with where the trailling arm isn't as horizontal.

[williamsvts]

are you not making this more complicated than it is?

that is just because of its position, it still moves the same circular distance (around the beam), just because its position has changed means the car will go more up and down. the spring rate still remains the same.

[Toad]

Yes, the torsion bar is still the same, so it will still twist the same amount with the same force etc... However...

Here's some pics to help describe what i'm trying to get at...

First pics shows a standard non-lowered Saxo and the 2nd pic shows a lowered Saxo. When the same amount of coil or twist takes place with the torsion bar, you can see that on the lowered Saxo, there is a greater amount of vertical movement. Basically, if the trailling arm was nearly at 6 o'clock, you would get mostly horizontal movement to the car, whereas the nearer the trailling arm is to 3 o'clock will give you more vertical movement of the car.

Standard Saxo:

http://i17.tinypic.com/8bjrpjn.jpg


Lowered Saxo:

http://i4.tinypic.com/81rlaxg.jpg

So this greater amount of vertical movement is what makes it "floppy."

[williamsvts]

it still doesnt change the spring rate, it just changes the direction of teh movement and where it happens.

[williamsvts]

if that was the case it would mean that lowering your car even with a full sus kit would have a negative effect on teh handleing. front going harder and teh rear going softer.

[AXracing]

lol i have mine dropped 90mm its still fine with some one in the back. catches on the odd speed bump nothing major. You will have no problem.

Um so you have you just cut down your bump stops and are running with no suspension :ponder:

[KamRacing]

and stiffening the front without doing the rear as well changes the handling of the car. Makes it more prone to understeer.

[Toad]

I've spoken to a couple of people on PGTI who experienced the same thing when lowering. They noticed the rear went "floppy" and used adjustable dampers to help the movement. I'm not kidding, when I lowered the rear, you could push down on the boot with one finger and bounce it up and down.

[KamRacing]

The torsion bar is in effect a linear spring. .. lowering doesn't change the spring rate just effectively changes the position of the spring (A perhaps oversimplified description). This is one of the reasons why I changed to a coilover setup on the rear of my 205 as I could tune the rear easier, have a progressive setup and handling nirvana. Its going one step further (or 3 lol) on the 309 with double wishbone suspension front and rear.. we'll see how that performs later in the year

Back on topic.. The problem when lowering a lot on torsion bars is that on big / high speed bumps the rear can go from a relatively soft spring rate to having effectively solid suspension when it hits the bump stop. I've seen at least one brown trouser moment on you-tube where this happens and an "oh christ" moment materialises

[Toad]

Slightly off-topic, (sorry) but if the rear axle setup on the Saxo / 106 GTI is so archaic, why are these cars said to have such great handling characteristics? I'm not disputing the fact, I'm just wondering... :ponder:

[KamRacing]

Just because it is ancient it doesn't mean they didn't get it right with the handling ;)

Things have moved on since then

[Toad]

So with the likes of the new Clio's that are out now, with much more modern suspension, would it be fair to say they handle much better? Or are the Saxo's / 106s still in the same leauge?

[KamRacing]

technically advanced suspension doesn't always make for superior handling but it certainly can do.

I haven't driven many of the newer hot hatches on the limit to compare

[AXracing]

As said its not really the basic design concept but actually how well the car is setup as a hole. Also older cars tend to be a lot lighter.

[theecho]

Cheers for the all the input people! Really helped! :D

Think I wont get it slammed as much! :)

[VTR_Dan_VTS]

Good diagram toad!
I have mine decked 60mm all round and its fine even with 2 huge blokes in the back. I got 15"s too.

[Toad]

Well yeah... There's a lot of room before you hit the bumpstops. Should be fine.

[wrighty_106]

i hav gt 16's on my car and just gt them sprayed up and dnt wanna put them on and that get sracthed to f**k straight away from hittin speeded bumps and pot holes so was just wonderin wats is the best way of sort of stiffen up the rear beam?? thanks

[Bickerton]

Dampers

[samfenna]

nice bump dickhead

[wrighty_106]

is that the black rubber bits or the back shock??

[mavoloso]

ive had 6 ppl in mine and mine dont catch at all on standard vts rims :s

loooll how dd u manage that

[KamRacing]

i hav gt 16's on my car and just gt them sprayed up and dnt wanna put them on and that get sracthed to f**k straight away from hittin speeded bumps and pot holes so was just wonderin wats is the best way of sort of stiffen up the rear beam?? thanks
you need to fit a stiffer torsion bar. This is your rear spring. Stiffer dampers will not help.

nice bump dickhead

Better than starting a new thread, when theres a current one that can be used.