understeer/oversteer in fwd saloon

[stockhatcher]

hi,

i need a few ideas as to how to change the handling of my pug 106 race car from being... evill to something more benign.

i have turn in understeer, followed by power oversteer ( yes in fwd). the only adjustments i can make are to tyres presssure and damper setttings. the car runs on road yoko a 539's with 60 profile.

so what would happen if i stiffen the front dampers, increase front tyre pressures?

what would happen if i reduce rear dampers settings and tyre pressures?

currently it is set up with 2.5 deg neg front camber, 12 clicks from soft, and 30 psi on the front and 18 clicks from soft, 32 psi in the rear.

i want it to stop sliding from the rear so much and reduce understeer.

i have put new tyres onthe front and old ones on the rear.

i have a link to the in car footage if you need to see it in action ( would rather not post it on here)

any advice is welcomed.

tia.

[leorest]

I'm not knowledgeable enough to help you with settings but I did read a useful nugget of information which said you should only tackle one effect at a time. This sounds like sound common sense to me. So don't try to fix under-steer and over-steer by changing several things at once because you will never know which change gave the appropriate result.

This is standard fault finding technique which can be applied to most problems in life.

Best of luck and enjoy experimenting with different settings.

[stew-typeR]

what are the toe settings at on the front? id recommend running 1-2mm toe out. better turn in for a start.

are the dampers bump and rebound adjustable? or just rebound?
what are the spring rates on the front? standard torsion bars and ARB in the back?

if you set the tyre pressures up about equal front and rear it might help a bit.
you wanna get the car understeer(slightly) in all conditions first, then small changes like tyre pressure, damper settings etc can be tweaked to adjust the balance.

[CombeMarshal]

You could try going to a race track on race day (ie Combe!) and getting a paddock pass and interigate a few drivers, we have a few Pug's at Combe

[Hirich]

stockhatcher said:

My pug 106 race car...currently it is set up with 2.5 deg neg front camber, 12 clicks from soft, and 30 psi on the front and 18 clicks from soft, 32 psi in the rear.

Horses for courses, all cars are different and all that, but this rings alarm bells. You are running a FWD car with a forward weight bias, stripped out (which has probably moved the bias even further forward). Yet you have higher tyre pressures and stiffer dampers at the rear? Is it possible that the settings you've got have been mixed up?

Now the quick way to get an answer would be to ask someone with a similar car (make sure it's one that does handle well...)

From a testing point of view my suggestion (which isn't worth that much) is that the initial understeer may be due to a soft front end, and the oversteer due to a too stiff rear (once it has loaded up). I would suggest that the rear end problems are costing you more time, so leave the front alone and work on the rear.
- Try a drop to 28psi and assess. As necessary play, until you feel an improvement in rear stability.
- With the new pressure, now play with the dampers. Start by dropping to 8 clicks (so very soft). this should show a significant movement, whether good or bad. Now move up to 12 clicks
This way, you should get the rear to work with your existing front, and you should get a feel for how you will control the oversteer.
Now, leave the rear alone (with the new settings), and work on the front. I would suggest you try adding 2psi at first.

One tip: As an amateur, you will find it difficult to set consistent times. So whilst you have a mate on the stopwatch, trust what you feel. Once you have played with a few settings, and believe you have made an improvement (and note that the tyres will be warmer, and you will be driving better), do go back to your original settings to confirm whether you really have made an improvement.

A tyre pyrometer would also be very helpful (plus a spannerman willing to jump around the car) to note inner, middle and outer temps - this shows up an awful lot of information about what the tyres are doing. It doesn't need to be professional, just a cheap infra-red or Gunson's multimeter, a notebook to write it down, and a quick spannerman to shout out the results.

A general caveat - it's far too long since I did any of this (and never in adequate depth), and I know nothing of 106s. There are others on here who should know better, and will hopefully confirm or debunk my theories.

[stockhatcher]

cheers for the tips.


the dampers are rebound adjustable only, rear arb is standard for the car - regulations state this, torsion bars are 23mm, up from 21.

talking to the majority of the other drivers, they run their cars full hard at the rear, 24 clicks, with upto 45 psi in the tyres. i've tried that and its.... interesting.

softening the rear goes against the percieved way to set up a stock hatch , however i feel that might be the way forward with this car, and then stiffen the front. i may also put slightly less worn rear tyres on.

[stew-typeR]

well the higher the setting on the dampers, the more loads transfer on that axle. thats one thing.

sounds like the front is the bigger problem to me. maybe a fraction too soft a spring rate. up the damping a little. do you know the toe settings? some toe out will aid turn in and be a bit neutral mid corner.

[denisb]

Before doing ANY of the above, check the basics.

Is your suspension bottoming out in any way (check damper travel, suspension component clearance, coil binding)?

Do you have any worn/damaged bushes, links, bearings etc?

Is the geometry correct (tracking, castor, camber, bump steer)?

Are you tyre temps correct across the tyre (you need a tyre probe for this, but they are worth every penny)?

Slightly contentious but turn in understeer can be caused by poor turn in technique (turning in too early, too sharply or at too high a speed). Your right about the power on oversteer, this shouldn't happen in a FWD car. This could be caused by something bottoming out or being 'wonky', or it is possible it started building up mid corner and you hadn't noticed.

Once the above is OK then you can look at springs/dampers etc.

[havoc]

Couple of thoughts to add to the above debate:-

- you're running track-stiff suspension with high-sidewall tyres...that's going to put a lot more work on the tyre sidewalls under cornering, and you'll experience a fair bit of flex as they load/unload. This might be (part of) the cause of the odd behaviour.

- what toe and camber setting are you running front and rear? Do you have rear toe-out? Do you have asymmetric settings?

I can't see you getting true power oversteer unless you've one of the following:-
- excessive rear toe-out
- suspension 'bottoming out' at the rear
- excessive weight transfer forwards removing too much weight from the loaded rear wheel
- too-aggressive turn-in style (causing 2nd or 3rd point to happen), but it sounds like it happens mid-corner, which is different, unless you don't pick it up initially.


Can you test it on larger alloys (lower-profile tyres), see if that makes any difference? Can you race on larger alloys?

[Hirich]

Trust Dennis on this. His posts on similar topics have always been well informed. Do the basics first.

While most pyrometers are £100+, DT have a £30 cheapo (and as I said, a Gunsons multimeter may have a temp unit included) - for your initial work a cheapo version should do OK. When we converted a mate's Se7en to ACB10s the tyre temp gave us a lot of information (particularly why we were damaging the outer edge). Over the course of a fag to think about what we had learned, we were able to set pressures and roll bars quickly into the right zone. Within an hour we had much better temps, a much more stable ride, and perhaps a second per lap of Llandow. I have no idea how long it would have taken us otherwise.

And another tip. A short course like Llandow or Curborough is ideal for you for this sort of work. Just make sure you have a mate to help out and pack him some lunch!

[stockhatcher]

denisb said:

Before doing ANY of the above, check the basics. Is your suspension bottoming out in any way (check damper travel, suspension component clearance, coil binding)? Do you have any worn/damaged bushes, links, bearings etc? Is the geometry correct (tracking, castor, camber, bump steer)? Are you tyre temps correct across the tyre (you need a tyre probe for this, but they are worth every penny)? Slightly contentious but turn in understeer can be caused by poor turn in technique (turning in too early, too sharply or at too high a speed). Your right about the power on oversteer, this shouldn't happen in a FWD car. This could be caused by something bottoming out or being 'wonky', or it is possible it started building up mid corner and you hadn't noticed. Once the above is OK then you can look at springs/dampers etc.

rear geometry is parallel for the wheels, no castor, front, has no toe out, but iirc it should have 1.5 deg.

wheel bearings have been replaced last month, tyres and wheels are set in regs so i can't do anything about them.

the oversteer is probably building up on turn in, and being noticeable from mid corner.

take a look at this in car link ( it ends with a crash ) i'll only leave it up here for a few hours as i'm a sensitive soul - now removed

>> Edited by stockhatcher on Friday 21st April 19:06

[selbymsport]

You have a tyre problem. The front tyre is most heavily loaded on turn in so the car will understeer as the heat builds in the tyre so the grip increases unfortunatly the rear tyre is not working so hard and will not heat up sufficiently and the grip balance front to rear causes oversteer. put new tyres on rear of car to solve problem or swap tyres front to rear and have an understeering car throughout the corner!
TIP:- you cannot set a car up with old or odd tyres