Suspension set up
Discussion
I was so impressed with my new adjustable suspension on the front of the car (needed due to cracked springs) that i have bought some for the rear. The only problem is they appear to be too soft.
Having had the springs tested the fronts are 225lb and the rears are 250lbs. This has greatly confused me as the front is nice and stiff (you can hardly manually push the car down) but the rear on harder springs is like jelly in comparison.
I know that the angle of the suspension members and the fact that the rear of the car has trailing arms may have something to do with it but i do not fully understand what.
Has anyone got any ideas?
I use the car for a number of track days as well as sunday trundles and want to get it right.
Cheers in anticipation.
Having had the springs tested the fronts are 225lb and the rears are 250lbs. This has greatly confused me as the front is nice and stiff (you can hardly manually push the car down) but the rear on harder springs is like jelly in comparison.
I know that the angle of the suspension members and the fact that the rear of the car has trailing arms may have something to do with it but i do not fully understand what.
Has anyone got any ideas?
I use the car for a number of track days as well as sunday trundles and want to get it right.
Cheers in anticipation.
The springs have less leverage at the back. At the front, the wheel rate (the thing that matters) is roughly half the spring rate. At the back, because of the reduced leverage, it is roughly one third of the spring rate. However, the spring rates you have sound about right to me for a normal road setup, and in any case just jumping up and down on the car you're probably measuring stiction in the bushes and dampers rather than the actual suspension stiffness. How does the car feel on the road? If the back is really too soft, you will feel it pitching a lot over long undulations.
the damper will have more effect than the spring on this .. the rear needs to be soft to get traction but those spring rates sound too soft anyway .. presumable you're on a damper that alters the bump as well as the rebound, if you're using gaz / avo / redline then the bump is altered as much as the rebound proportionately, something like the Nitron / hlins alters the rebound mre than the bump proportionately in which case you can have the transient effect of stiff springs by winding the damping up on the avo / redline / gaz route but this isn't really what you want since during cornering the car will still assume a high roll angle cos the roll stiffness isn't affected by the damper. I would suggest over 300 lbs on the front and wind some damping off and leave the rear as it is - make the car stable from the front first and see how yu go from there. if the rear is stil too soft wind the damping up a bit but be careful about being too aggressive on this or you'll find yourself with corner entry oversteer as the stiff damping resists the moement of the suspension .. if that's happening go slightly up o the spring rate and wind the damping back off again until you rech a point where the car exhibits similar balance on corner entry and then throug the corner. On a V6S you've ot got a great deal of power to overcome any understeer you may generate so you might want something slightly tail happy anyway - but seeing how fast you were at bruntingthorpe I think you will cope with a playful rear end (!)... 
>> Edited by joospeed on Monday 7th April 18:55
>> Edited by joospeed on Monday 7th April 18:55
I was so impressed with my new adjustable suspension on the front of the car (needed due to cracked springs) that i have bought some for the rear. The only problem is they appear to be too soft.
Having had the springs tested the fronts are 225lb and the rears are 250lbs. This has greatly confused me as the front is nice and stiff (you can hardly manually push the car down) but the rear on harder springs is like jelly in comparison.
I know that the angle of the suspension members and the fact that the rear of the car has trailing arms may have something to do with it but i do not fully understand what.
Has anyone got any ideas?
I use the car for a number of track days as well as sunday trundles and want to get it right.
Cheers in anticipation.
Where did you get the springs from as i believe mine are on the way out
Thanks chaps, joospeed got it exactly right (not that this was ever any kind of test), it would seem i have been stiffening the front dampers to compensate for the softness of the springs. As the dampers do not work as effectivley at their extremities i need to fit stiffer springs.
The springs may be suitable for road use but for track driving i feel they do need to be stiffer and i am prepaired to live with the consequences on the road.
The dampers are redine and have only one adjuster for bump and rebound which for my limited abilities are ok at this moment. (I think i would need to go back to college to learn how to set up anything more complicated, this is like another language to me
)
The plan for the moment is to move the 250lb springs to the front. This may not prove to be stiff enough but at this stage it saves buing yet another set of springs.
The only thing is what to do with the rears. should the rear set up be softer than the front? or taking into account the fact that the rear has trailng arm suspension and different geometary does it need to be stiffer and if so by what proportion?
Ever wish you had'nt started something?
Yours, very confused,
Taffstalini!
>> Edited by taffstalini on Tuesday 8th April 17:06
The springs may be suitable for road use but for track driving i feel they do need to be stiffer and i am prepaired to live with the consequences on the road.
The dampers are redine and have only one adjuster for bump and rebound which for my limited abilities are ok at this moment. (I think i would need to go back to college to learn how to set up anything more complicated, this is like another language to me
) The plan for the moment is to move the 250lb springs to the front. This may not prove to be stiff enough but at this stage it saves buing yet another set of springs.
The only thing is what to do with the rears. should the rear set up be softer than the front? or taking into account the fact that the rear has trailng arm suspension and different geometary does it need to be stiffer and if so by what proportion?
Ever wish you had'nt started something?
Yours, very confused,
Taffstalini!
>> Edited by taffstalini on Tuesday 8th April 17:06
spivvy said: [
Where did you get the springs from as i believe mine are on the way out
You should be able to get them from any TVR dealer/parts supplier. The trick seems to be getting the right size and lb rating to suit your current settings. Do you know what is currently fitted to the car?
taffstalini said:
spivvy said: [
Where did you get the springs from as i believe mine are on the way out
You should be able to get them from any TVR dealer/parts supplier. The trick seems to be getting the right size and lb rating to suit your current settings. Do you know what is currently fitted to the car?
as far as i can make out they are the original factory fitted springs and dampers
taffstalini said:
The plan for the moment is to move the 250lb springs to the front. This may not prove to be stiff enough but at this stage it saves buing yet another set of springs.
The only thing is what to do with the rears. should the rear set up be softer than the front? or taking into account the fact that the rear has trailng arm suspension and different geometary does it need to be stiffer and if so by what proportion?
O.K - So I should go for 250 lb springs on the front - so what about the back - any ideas - oh and we are talking about a V8S here - where is HarryW when you need him?
I've checked back through my notes and found the original spring rates on my V8S were 210/300 rising rate at the front and 180/270 rising rate at the back. At normal ride height they are in the 'soft' part of their rate so for the purposes of handling calcs, you can treat them as 210 and 180 lb/in. That corresponds to a rate at the wheel of 105 lb/in front and 60 lb/in rear.
By my calculations the 7/8" anti-roll bar provides roll stiffness equivalent to an extra 100 lb/in on the front spring rate although if you remove the rubber bushes you can increase this to around 140 lb/in. (The V6 models have a thicker bar which is about 50% stiffer.) These rates are all relatively low and may be why the car is so predictable to drive, but also why it corners on its door handles and wallows so much. You can afford to increase the spring rates substantially without making the car too impractical for normal road use, and for a track setup you could double or even trebble the stiffness, but you have to bear in mind as you do this the car will respond quicker (so your reactions need to be that much faster) and will break away more abruptly when starts to slide. No need to be too worried about this if you're happy with your ability to control the car as standard, and not making really dramatic changes in the setup. Just something to bear in mind while you're deciding what changes to try. Obviously, this would also give a harsher ride which is probably more important to most of us. Finally, you would want to stiffen the dampers as you stiffen the springs. For small changes this just means an extra click or two on your adjustable dampers but for bigger changes you might need to have the dampers revalved. (My Nitrons were valved to suit my springs.)
The ratio of roll stiffness between the front and rear of the car has a big effect on the balance of the car in cornering, i.e. stiffening the front promotes understeer, stiffening the rear promotes oversteer. If you're changing the springs it is a good idea to keep this ratio the same to keep the handling neutral. In simplistic terms, if you double the rate at the front you need to double the rate at the back to match. However, you also need to bear in mind that the front antiroll bar increases the front roll stiffness substantially and you need to factor this in. The thing you are actually trying to keep constant is F+B/R where F is front spring rate, B is the front roll bar equivalent spring rate and R is rear spring rate. For example, with the standard V8S springs this works out to (210+100)/180 = 1.7 ish. Supposing you decide to put 250 lb/in springs on the back, the front spring rate to match this works out as (F+100)/250=1.7, F = (1.7*250)-100 = 325. Don't put *too* much store by the exact values, small changes to the balance don't matter unless you're racing, and there are other factors that affect the balance that are being ignored here, but if you use these values as a guide to the sort of rates you want, you can be confident that the handling balance of the car won't change dramatically.
Hope this helps, and thanks for reading this far!
Peter Humphries (and a green V8S)
By my calculations the 7/8" anti-roll bar provides roll stiffness equivalent to an extra 100 lb/in on the front spring rate although if you remove the rubber bushes you can increase this to around 140 lb/in. (The V6 models have a thicker bar which is about 50% stiffer.) These rates are all relatively low and may be why the car is so predictable to drive, but also why it corners on its door handles and wallows so much. You can afford to increase the spring rates substantially without making the car too impractical for normal road use, and for a track setup you could double or even trebble the stiffness, but you have to bear in mind as you do this the car will respond quicker (so your reactions need to be that much faster) and will break away more abruptly when starts to slide. No need to be too worried about this if you're happy with your ability to control the car as standard, and not making really dramatic changes in the setup. Just something to bear in mind while you're deciding what changes to try. Obviously, this would also give a harsher ride which is probably more important to most of us. Finally, you would want to stiffen the dampers as you stiffen the springs. For small changes this just means an extra click or two on your adjustable dampers but for bigger changes you might need to have the dampers revalved. (My Nitrons were valved to suit my springs.)
The ratio of roll stiffness between the front and rear of the car has a big effect on the balance of the car in cornering, i.e. stiffening the front promotes understeer, stiffening the rear promotes oversteer. If you're changing the springs it is a good idea to keep this ratio the same to keep the handling neutral. In simplistic terms, if you double the rate at the front you need to double the rate at the back to match. However, you also need to bear in mind that the front antiroll bar increases the front roll stiffness substantially and you need to factor this in. The thing you are actually trying to keep constant is F+B/R where F is front spring rate, B is the front roll bar equivalent spring rate and R is rear spring rate. For example, with the standard V8S springs this works out to (210+100)/180 = 1.7 ish. Supposing you decide to put 250 lb/in springs on the back, the front spring rate to match this works out as (F+100)/250=1.7, F = (1.7*250)-100 = 325. Don't put *too* much store by the exact values, small changes to the balance don't matter unless you're racing, and there are other factors that affect the balance that are being ignored here, but if you use these values as a guide to the sort of rates you want, you can be confident that the handling balance of the car won't change dramatically.
Hope this helps, and thanks for reading this far!
Peter Humphries (and a green V8S)
Top reply Peter 
, after going round the corners on my door handles mpre than once 
this is just the sort of thing needed. Re the uprating the springs, at what point, asuming the 'standard' shocks are not defective and are retained, do you need to think about changing the shocks for something a little more 'sporting'.
Harry
PS Ren for all things technical I think you'll find Peter more than qualified, me I just listen and if I've got anything of value to add I will, which in this case I have not
, after going round the corners on my door handles mpre than once this is just the sort of thing needed. Re the uprating the springs, at what point, asuming the 'standard' shocks are not defective and are retained, do you need to think about changing the shocks for something a little more 'sporting'. Harry
PS Ren for all things technical I think you'll find Peter more than qualified, me I just listen and if I've got anything of value to add I will, which in this case I have not
Richard set up and modified the 520 when it had a 390 engine and did a superb job. I ran those setting for the first two years of its 520 life as well and have only now started to change things now that the car competes on slicks.
It is worth working out what you want from the car in terms of handling before spending money. It is also worth not changing things after a set of mods until you have got used to the feel. Also bear in mind that the driving style can also induce handling problems. Worth experimenting with different lines and smoother styles before accusing the car of under or over steer.
It is worth working out what you want from the car in terms of handling before spending money. It is also worth not changing things after a set of mods until you have got used to the feel. Also bear in mind that the driving style can also induce handling problems. Worth experimenting with different lines and smoother styles before accusing the car of under or over steer.
Gassing Station | S Series | Top of Page | What's New | My Stuff