If you think about what happens when you lower the mount for the top arms or lower the whole rear suspension you should see how it forces the roll centre higher.
M@
Panhard V No panhard rod.
Started by
rodomo
, Dec 30 2007 09:25 AM
206 replies to this topic
#101
Toranamat69
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Posted 10 February 2008 - 12:04 AM
This pic shows how you determine where the roll centre is on a Torana style rear end.
If you think about what happens when you lower the mount for the top arms or lower the whole rear suspension you should see how it forces the roll centre higher.
M@
If you think about what happens when you lower the mount for the top arms or lower the whole rear suspension you should see how it forces the roll centre higher.
M@
#102
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Posted 10 February 2008 - 10:59 AM
^ Can not read it sorry.
#103
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Posted 10 February 2008 - 11:37 AM
This should be a bit better.
M@
M@
#104
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Posted 10 February 2008 - 07:16 PM
Hmm that picture looks familiar. Learnt heaps from that book, had to read it a few times to get my head around some of the concepts though.
#105
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Posted 14 February 2008 - 09:31 PM
gday guys, may have missed some of your points. jst letting you know. i use an adjustable watts linkage setup in my lx 4dr, and i highly recomend fitting some form of panhard or preferble watts linkage if your seeing track work. one problem with running either setup is. as was mentioned it lowers or tricks the car into having a lower rear roll centre. this will cause the front end of the car to sometimes react not in a psitive nature coz the roll centre is still wrong at the front. im working on correcting this in my own car.
#106
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Posted 14 February 2008 - 10:25 PM
I'll just add oi, oi, oi and welcome to the forum 
#107
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Posted 14 February 2008 - 11:08 PM
That's you is'nt it Darren.......wondered how long it would take you to get on here, hahagday guys, may have missed some of your points. jst letting you know. i use an adjustable watts linkage setup in my lx 4dr, and i highly recomend fitting some form of panhard or preferble watts linkage if your seeing track work. one problem with running either setup is. as was mentioned it lowers or tricks the car into having a lower rear roll centre. this will cause the front end of the car to sometimes react not in a psitive nature coz the roll centre is still wrong at the front. im working on correcting this in my own car.
Dave
#108
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Posted 15 February 2008 - 09:25 PM
--------------------
Updates to come, watch this space........
Location: Perth
F@#$ing 'urry up !
Welby
#109
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Posted 15 February 2008 - 11:03 PM
Yeah yeah yeah keep your pants on, there will be more during next week, will have welded panhard mounts to the car. Will finalise design for the machinist to knock up for the spindle on the diff.
Dave
Dave
#110
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Posted 17 February 2008 - 02:25 AM
Speaking of roll centres, in theory shouldn't front and rear roll centres be at the same height? And be at the same height as the cars C of G?
#111
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Posted 17 February 2008 - 08:13 AM
In theory yes.....
Practicallity and packaging almost always dictates that the CofG is higher at least in the front of a sedan anyway, which is what most of this is about.
A car with the CofG and roll centres at the same height will be very hard to drive "on the edge" it will be twitchy and unpredictable. Schumacher could probably handle it, but the rest of us would smudge it into the fence on the first high speed turn.
Practicallity and packaging almost always dictates that the CofG is higher at least in the front of a sedan anyway, which is what most of this is about.
A car with the CofG and roll centres at the same height will be very hard to drive "on the edge" it will be twitchy and unpredictable. Schumacher could probably handle it, but the rest of us would smudge it into the fence on the first high speed turn.
#112
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Posted 17 February 2008 - 09:55 PM
Then lets talk specific applications. LH - UC Torana with alloy V8 and 9". For Joe average, about how far off the ground would you think the roll centres should be? I realise this is a guide only and will be treated as such.
#113
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Posted 17 February 2008 - 11:18 PM
Front @ 4" above ground.
Rear @ 8" above ground.
with a ride height of 4"
Will take plenty of custom fabrication work to get them there though.
Realistically, if you can get the front anywhere above ground level @ 4" ride height you are doing well.
Rear put a panhard or Watts in it and that will define your roll centre height for you.
Rear @ 8" above ground.
with a ride height of 4"
Will take plenty of custom fabrication work to get them there though.
Realistically, if you can get the front anywhere above ground level @ 4" ride height you are doing well.
Rear put a panhard or Watts in it and that will define your roll centre height for you.
#114
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Posted 18 February 2008 - 12:56 PM
Thanks for the guide Greg. I have only recently decided to get interested in suspension fabrication, so I thought I'd better get some guidelines on what to aim for.
#115
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Posted 18 February 2008 - 09:38 PM
I suppose the next question is, if I can't get the front roll centre above ground level, would that alter where you would want the rear roll centre?
#116
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Posted 18 February 2008 - 10:07 PM
Yes it most definately does.
That is your "roll couple" and if it is too angled down in either direction it causes non linear weight shift and poor transitional handling. In short the car will handle like shit.
Too far down at the front will tend to understeer. and vise versa for the rear, unless of course you prop the offending end up with super hard springs...... Which is why most Racing Toranas run greater than 1000lbs up front.
That is your "roll couple" and if it is too angled down in either direction it causes non linear weight shift and poor transitional handling. In short the car will handle like shit.
Too far down at the front will tend to understeer. and vise versa for the rear, unless of course you prop the offending end up with super hard springs...... Which is why most Racing Toranas run greater than 1000lbs up front.
#117
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Posted 18 February 2008 - 10:19 PM
So that said Greg, you still recommend running 1000lb or heavier springs in the front? I had it in my head for some unknown reason that it wouldn't be required with the improved rubber we have now over the 70's, why I thought that would make a difference I dont know.
Dave
Dave
#118
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Posted 18 February 2008 - 11:26 PM
This is a pleasure discussing this with you Greg. You are explaining it in a way in which I can understand things. Unlike the couple of books I have read.
So the ideal solid rear suspension for an LH - UC would be a parallel 4 link with an adjustable watts linkage?
So assuming that:
(1) I'm happy with the spring/shock/sway bar combo and
(2) A tyre pyrometer indicates consistent temperatures across the tyres and
(3) I'm not using a mini/full spool or detroit locker
then adjusting the rear roll centre would then be the best way to alter understeer or oversteer?
So the ideal solid rear suspension for an LH - UC would be a parallel 4 link with an adjustable watts linkage?
So assuming that:
(1) I'm happy with the spring/shock/sway bar combo and
(2) A tyre pyrometer indicates consistent temperatures across the tyres and
(3) I'm not using a mini/full spool or detroit locker
then adjusting the rear roll centre would then be the best way to alter understeer or oversteer?
#119
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Posted 19 February 2008 - 07:05 AM
Firstly...
Dave,
1000lbs or greater will almost always be required in a racing Torana. Why? Because it is near impossible to get the roll centre up high enough (closer to the CofG actually) so as you can drop the spring rate below that.
Chopper,
Yes the parallel with Watts is ideal.
I wouldn't make a roll centre change to dial out understeer/oversteer unless it was a BIG push.The problem with using roll centres to adjust car balance is that a small change in height can yield a large change in handling characteristics. The other reason you should use bars and springs to tune your under/over steer is that you are only changing one thing at a time when you make a bar change. When you make a roll centre height adjustment it changes the roll couple angle so the jacking effects are altered at BOTH ENDS of the car.
Is it getting complicated again?
Dave,
1000lbs or greater will almost always be required in a racing Torana. Why? Because it is near impossible to get the roll centre up high enough (closer to the CofG actually) so as you can drop the spring rate below that.
Chopper,
Yes the parallel with Watts is ideal.
I wouldn't make a roll centre change to dial out understeer/oversteer unless it was a BIG push.The problem with using roll centres to adjust car balance is that a small change in height can yield a large change in handling characteristics. The other reason you should use bars and springs to tune your under/over steer is that you are only changing one thing at a time when you make a bar change. When you make a roll centre height adjustment it changes the roll couple angle so the jacking effects are altered at BOTH ENDS of the car.
Is it getting complicated again?
#120
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Posted 19 February 2008 - 09:33 AM
I've been experimenting with different size rear sway bars on my Commodore, and the difference is amazing on the track, the car can be great at one turn and understeer at the next, put a slightly larger rear bar on and now it oversteers at the first corner and is great at the next !!!
Adjustable bars would make all this much easier, but there is a few items ahead of them on the shopping list at the moment.
Adjustable bars would make all this much easier, but there is a few items ahead of them on the shopping list at the moment.
#121
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Posted 19 February 2008 - 11:52 AM
It still makes sense Greg. Just trying to work out what can and can't be done.Chopper,
Yes the parallel with Watts is ideal.
I wouldn't make a roll centre change to dial out understeer/oversteer unless it was a BIG push.The problem with using roll centres to adjust car balance is that a small change in height can yield a large change in handling characteristics. The other reason you should use bars and springs to tune your under/over steer is that you are only changing one thing at a time when you make a bar change. When you make a roll centre height adjustment it changes the roll couple angle so the jacking effects are altered at BOTH ENDS of the car.
Is it getting complicated again?
#122
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Posted 19 February 2008 - 10:40 PM
Front @ 4" above ground.
Rear @ 8" above ground.
with a ride height of 4"
That seems to be the figures that keep popping up with guys who race these cars around circuits so that's certainly the sort of figures I would be shooting for.
Some go for a slightly higher than that.
M@
#123
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Posted 19 February 2008 - 10:53 PM
yeah dave its me, your pretty quick. got to remember, where the springs is mounted in relation to the the suspension arm causes a leverage affect, this is also why toranas require such hard front springs. the spring dosent act directly at the wheel. i think it may even be a 2 to 1 ratio. the spring effectively needs to be twice as hard to control suspension movement. the springs on front of commodores act directly to movement thats why they are normally no where near the same poundage rate.
best thing you can do is mount lower mount of the shock and the spring as close as possible to the outside lower ball joint, then you could reduce the rates.
best thing you can do is mount lower mount of the shock and the spring as close as possible to the outside lower ball joint, then you could reduce the rates.
#124
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Posted 19 February 2008 - 11:11 PM
Good point^
Motion ratio on a Torana is 2:1
Meaning that a 1000lb spring will yield a wheel rate of 500lbs.
Keep in mind though that 1000lb is still a conservative number as I run 1600lbs in the front of my XU-1, and it turns well.
M@, the reason behind those numbers is that is what is achivable without a MAJOR re-engineer of the whole front end...
(serious stuff as you know)
Hey Mick..... is the Commo consistent on both lefts and rights? Or does it understeer on one and oversteer on the other?
Motion ratio on a Torana is 2:1
Meaning that a 1000lb spring will yield a wheel rate of 500lbs.
Keep in mind though that 1000lb is still a conservative number as I run 1600lbs in the front of my XU-1, and it turns well.
M@, the reason behind those numbers is that is what is achivable without a MAJOR re-engineer of the whole front end...
(serious stuff as you know) Hey Mick..... is the Commo consistent on both lefts and rights? Or does it understeer on one and oversteer on the other?
#125
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Posted 20 February 2008 - 09:19 AM
Hard to say, at Phillip Island it understeers at Southern Loop and Siberia, both left handers, but there aren't really any comparable right handers,Hey Mick..... is the Commo consistent on both lefts and rights? Or does it understeer on one and oversteer on the other?
At the end of the day, I figure there are Commodore Cup cars with panhard rods going around P.I. in under 1.48 which is good enough to be on the front row of a state level I.P. grid so the panhard rod isn't too much of a limiting factor. Not as much as the driver anyway....
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