Hi,
Sorry to ask a question which has probably be anwsers many times but here gos. Im looking to setup my indy blackbird for a couple of trackdays at
donnington park and wondered what spring rates would be ideal. I currently get a lot of rear end roll so I wanted to reduce that. I don't mind
if it would be a handfull on the road as I can always put my current springs back in for road use.
thanks
What are they currently? You also want to match front and rear. I read an excellent post about this on WSCC forum but they run ARBs on their cars:
quote:
do you have anti roll bars?
if so try something like 350 front 250 rear , run the bars soft ....
set the bars front to rear to find a balance you like
then how consistant are you on lap times in say a 30 minute session?
if withing 10ths once tyres are warm try stiffening the bars equally and seeing what it does to lap times , if you go up and you get quicker keep going till one of the other bars is full stiff , you then need a stiffer spring that end ..... fit 20lbs stiffer and repeat.
Obviously equally slacking off both bars again .....
if you go slower by stiffening the bars go the other way .... if times improve up to the point where one end is full soft then drop 20lbs ......
to be fully honest its all about testing , and consistant testing at that , and remember there is a reason teams bin seemingly good slicks after 40 to 50 laps. So be careful you don't end up chasing tyres going off rather than an actual handeling issue.
Mark,
what rate springs do you currently have fitted?
Phil
I'm not exactly sure. Its what was supplied by mk for a bike engined car. I'm going to take them off and have a look when I can find time.
There's the same conversation going on in another board I use, someone posted this about Nitrons but I think the info is generic enough:
quote:
With respect to adjusting the Nitrons, I guess it depends whether you have them installed upright or upside-down?... I fitted them upside down (with the adjuster at the bottom) to keep the un-sprung mass down. With them in this upside-down installation to firm them up you turn the adjuster clock-wise when looking from above (although there should be a [+< >-] indication sticker so you can’t go wrong). Nitron calibrate there dampers at the full hard setting so logic would suggest the further away from full hard you go the more variation between dampers there will be, which is why Nitron settings are always stated from full hard. As to what setting you need – all about feel. The spring rates are the major influence in chassis balance and if Nitron know what they are doing they should be able to advise and supply appropriately (as I think they do – I’m happy). With the fixed ratio dampers we have, the ability to really stuff the bump/rebound ratio up is removed (as I’m sure I could get it really wrong J ) so all we have to do is find a setting that suits the road/track surface. Bumpy road surfaces toward the soft setting and perfectly smooth track toward the firm – no need to worry about the B/R ratio as Nitron sorted that out. As to using the damper to adjust chassis balance – they are only for fine tuning so the starting point should be equal clicks front to rear from full hard then see what the balance is - oversteer or understeer (you have to make a decision as to how firm/soft your starting point is, but middle is probably best). By firming, say the front damper relative to the rear you should start to induce slight understeer (or move toward understeer if you had oversteer). Tires and pressures can also play havoc, so I try to neutralise their variation by starting from cold with factory pressures and then over the first few sessions bring the pressures back to the factory settings so that when the tires are up to working track temp the pressures are only a little above the cold settings. That should prevent the tires from cooking but also keep a consistent handling characteristic. I don’t know enough on the subject really, nor do I want my track days to become test days where I’m consistently chasing settings – I just want to drive a good compromise and get the track time in. If you have an adjustable ARB, then set it full soft to start with, get the tires balanced as above, and then you should have two consistent handling influences stabilised (tires and arb) so you can work on the dampers. I bet three sessions would be enough to find it. This is really doing the absolute minimum too make the most of track day driving without getting too into the science. Once you understand your damper difference front to rear for balance then you can set them firm, soft, medium, whatever and maintain the difference and keep the balance good at any setting. It all changes if you change tires – different side wall stiffness etc effects the dynamic damping rates so you just need to start at equal damper settings again and see which way you need to go. If when doing the initial balance set-up you find you can’t tune out oversteer, then you will need to start bringing the arb in one setting at a time and then start again with the damper tweaking – if you do find you need more and more arb, then you should consider changing the front springs for stiffer. It would be unusual to have severe understeer in a car like the Elise (mid engine, rear drive etc), but if you did and the damper tweaking proved unsuccessful with the arb full soft then you would need to consider stiffer rear springs – of course there is a vice versa to stiffening the springs at one end of the car or the other as you could always go softer at the rear if you need to induce understeer rather than firming the front… hope that makes sense!
I should have added, I run 250 front and 175 rear. Protech. It's slightly too hard for the road and slightly too soft for the track. Hey ho. I'm still experimenting with damper settings.
Ours has 350lb on the fronts and 200lbs on the rear, as standard from MK.
It's not too bad on the road but not ideal for track, so we're gonna start playing around with the spring rates and damper settings as a
start, to try and eliminate some of the excessive roll.
TBH, I don't think you can compare spring rates used on kitcars other than MK Indys and even then, there are so many differing opinions out there
on what they should be. I think it's sometimes best to just find out for yourself and go with whatever suits your set-up and style of driving.
There are just too many variables for someone to be able to give you a definitive answer and it's not just about spring rates.
Phil
Did I remember that a while ago someone was working on a bolt on frame to move the rear upper wishbone mounts outboard and reduce roll?