Andy.F

Claudius

Sounds like your M3 was set up 'safe' ie predominantly an understeering car. With RWD, the weight transfer distribution in roll will mainly dictate the handling characteristics.

I used to race a rwd cossie and found that i had to increase the rear spring rates considerably to dial out corner exit understeer.
My final settings gave neutral handling at apex, slight understeer as i first applied light throttle, progressing to slight oversteer as i increased the throttle. This was perfect for early power application and a quick exit.
When i ran with softer rear springs, the car would just understeer as soon as throttle was applied mid bend.

FWIW my scoob with 50/50 diff just understeers everywhere on throttle

Mycroft

In the Torque/slip angle equation you must also account for loading, because power is delivered all round there is less weight applied to the front tyres on a RWD car. This loading also accounts for the high lateral 'G' that be experienced, in theory nothing that is 'holding' on of any given weight cannot exceed 1G as both the sideways and downward forces are equal, that is why the car leans over, the weight is added to the outer tyres and is acts on the (edit) Roll Centre as if a fulcrum forcing weight that is notional onto these tyres allowing you to actually attain or exceed 1G, the lower the (edit) Roll Centre the greater the G you can generate

[Edited by Mycroft - 8/19/2002 3:22:33 PM]

[Edited by Mycroft - 8/19/2002 5:20:07 PM]

Claudius

I do not know that, but I guess, since there are better drivers than myself, obviously. But they cant change the physics either, can they? I dont think you could load the front up much more, you would get the back out lots and just drift for a relatively long time when accelerating out.

Andy.F

What ? Are you saying weight transfer is actually good for increasing 'G' ? I don't think so ! Assuming you could achieve a C/G height of zero, that would give the maximum cornering force as there would be no weight transfer.

[Edited by Andy.F - 8/19/2002 3:42:02 PM]

Claudius

Andy! Now we're talking!

Absolutely.

Not exactly. It was loaded on the front, 30mm lower than std, and 20 mm lower in the rear. Not sure about the rear spring rate, probably something soft like 3N/mm to go with the Bilsteins, but it stuck well until very controllable oversteer initiated.

I had to do the same thing on my Evo It was a pure pleasure in the end, always slightly drifting out of corners

Yes, that's good. Ideally, I would like to get rid of that understeer bid, but it could be good as a safety margin if you enter a corner too fast.

Yes, because it "sits down" on the rear and the front loses grip. That's what I hate about RWD, they're all like that until you sort the suspension out.

That's what I keep telling all my friend who ask me about Subarus What's that due to, though? Isnt weight distribution 50/50? There seems to be a lot of problems with the initial set up: people make "bumpsteer" mods, install "anti lift kits" etc. No one seems interested in front diffs or adj. monotube suspension though (ok, that's expensive stuff...)

Claudius

As far as I am aware, you can even get the center of gravity BELOW the road surface. That's at least what an engineer told me. But I dont really care about that, since the lowest setting ride height wise is not the one that's best.

ex-webby

there is no way of getting the c/g below ground.. not unless you can run in a trough. I think you're thinking about the roll centre.

cheers

Simon

carl

Not true! You could drive over a bridge and have massive weights attached to the side of the car, that hang below the bridge

But given a level road, you're right

c/g = centre of mass. To get it below the road you need to have the majority of the mass below road level.

ex-webby

LOL.. sorry, forgot about the brige dynamics

I got really worried when I read the first two words of your reply!

Claudius

I thought of center of gravity? No idea, as I said

What spring rates and bump settings do you recommend with this set up?

Makalu

Dont you just Love ScoobyNet?

I havent a clue what they are all talking about but I read the whole thread from start to finish!

Mak.

ex-webby

that set-up only works well with 1 wheel drive vehicles. You need to keep the tightrope really tight and keep the power below 1 BHP (Brake Human Power).

Andy.F

Simon, stop muppetising this thread you should know better

Instead, suggest ways to get my scoob to stop pushing the nose o bad under (even light) power-----
Currently on Leda adjustables 325Fr 275Rr 22mm Rear arb. Std front arb -2.5deg front camber -1.0 deg rear, various toe settings tried front and rear, just compromise the straight line stabiliy, didn't seem to help mid corner. 10 psi less in the rear tyres helps but is not my preferred solution !!
It was on 225 lbs rear and the change to 275 helped, do you think i should go even higher at the rear or lower at the front ? or something else ?

cheer

Andy

Mycroft

My mistake, I meant roll centre! F1 cars run a roll centre at or below road level, if you take the roll centre at or below the final lower arm/bub connection then you get the 'excess' G ability.

Mycroft

And yes weight transfer is unavoidable (kinetics) and by lowering the RC you make use of it, it can be used, what you dont want in cars with simple suspension (ie anything that is not the classic twin wishbone) is to much compression of the system when subjected to this transfer, unless you have the full control of the geometry that only this system affords then the tyre is not attacking the suface at its optimum and will shoulder under and the cars behaves badly.

So tyres play a major part in all this but the control of the geometry is just as important, Macperson struts are good but are not good enough for real and accurate control, the Merc system is awful for such an expensive car and Porsche the same although the Weissach design was a good engineering fudge for a system that is really just an updated swing axle.

You have to have 4 pickup points on the chassis so as to control that very heavy wheel and tyre.

Andy.F

Disagree, You can drop the front and rear roll centres on a scoob below ground level by lowering the car 4 or 5 inches, the bottom arms will run uphill to the pivot point.

The car will just roll more, run out of suspenion travel and transfer weight via the springs/arb's/bump stops - been there, tried that, less grip !!

In theory the lower you run the car the less weight transfer will give increased grip, regardless of roll centre height.

Claudius

Yeah, that's what I meant, too

Mycroft

Lowering the suspension can raise the roll centre!

So just 'slamming' the car 4inches and having the arm 'running uphill' may well have been counter productive.

The first 3 door Cossie had a roll centre at about 260mm above the ground, and had a very low ground clearance, the last 4 doors had a decent ground clearance yet a roll centre of 190mm above the ground, this is very common.

The design must look at where the pick up points are located, better still having a twin front subframes assembly is the way to go, my car has a roll centre just 90mm above the ground yet I have 6½ inches of ground clearance, dropping the suspesion just 20mm ruduces the roll centre by 15mm dropping her 30mm takes her back to where she was at 90mm. we are talking only of the front, you want the rear RC to be higher so as to give a classic RWD accelerator pedal based steering.

[Edited by Mycroft - 8/19/2002 6:08:33 PM]

Andy.F

I can assure you that lowering a scoob front or rear WILL lower the roll centre, there are no upper arms to shorten the effective swing axle length and hence raise the RC.

Mycroft

I'll accept that.

I had to take glean the necessary info from the Workshop manuals and draw the diagram out for my car, someone here has obviously done that.

EvilBevel

Andy, I'm not an expert on this, but I talked about it a lot to people who should know (dodgy reference, I know) and I'd say:

1. change front diff to a mechanical one (ATB for example) to get a bit more bite, and reduce some off the power on understeer.

This however will not eliminate it completely, as I think the main problem with Subaru's (excluding possibly 22B's / type RA's) would be the centre diff.

I'm not sure if you were already driving a type RA, but a diff that distributes more power to the rear (say 40/60) might make a big difference.

Have you already tried the bumpsteer mod ? (which can help another part, but won't turn your car into an oversteering monster)

My car is pretty balanced at the moment, but also pretty dull in a way. Changes were DMS suspension, front Quaife ATB diff, bumpsteer, ALK, and stiffer rollbars front and back (adjustable at the back). In my opinion, it needs another centre diff (and possibly rear diff changed to ATB as well) to make it a really "handling" car. The trick diff mentioned in Drivetrain might also be an option.

Just my 2 cts etc.

Andy.F

Thanks for that I forgot to mention, I already have a mechanical front diff. This can help pull round the front but can also induce more understeer if it is already there
I wasn't sure if the anti lift would help so much as I have optimised the static camber at 2.5 degrees ?
I agree the answer is a rear bias centre diff want one now

Edited to add - Home made bumpsteer mod did help a bit

[Edited by Andy.F - 8/19/2002 6:33:09 PM]

Andy.F

Mycroft

The suspension diagram for the scoob roll centre is pretty simple, it's just a McPherson strut at each end with almost horizontal lower lateral links.

K9VYN [Kevin W]

Guys,

Very interesting topic - learnt a fair bit reading it. My personal preference is to have a car/setup that suffers neither from understeer or oversteer (impossible I guess, but I'd rather just go round the corner).

I have a '94 WRX. No manual diff control etc. Power may be up around 285bhp+ with the mods/engine work. I can now comfortably break traction with too much rpm from standing where as in standard form I couldn't even in the wet (or very rarely). Does this mean I am now putting more power through wheels than the setup can cope with or are my tyre pressures too high (35psi front)?

I'm currently running on 215/40/17s (Toyo T1-S). I found 205/40/17s much more positive (turn-in) when cornering - I guess due to the lesser aspect ratio of the tyre (Toyo T1-S).

The suspension has been tuned by Powerstation - toe-in/out, bump steer sorted etc (although may need another look due to travel on our potholed Notts roads). I have an anti-lift kit and front and rear uprated anti-roll bars (rear adjusted to middle position).

I have been advised that lesser tyre pressures at the rear will help check understeer. Is this correct? What about adjusting the rear bar fully? I suspect this may stiffen my cornering but perhaps make the car more difficult to control if the rear steps out? Are much lesser pressures at the rear a safe thing?

I am soon to be stepping up to 215/35/18s. I am considering adjusting up the rear bar to maximum for a trial and running 33psi front and 30/31psi rear. I guess the only way to know what suits my driving style is trial and error (as we all have different styles/preferences) - but perhaps some genral advice on my intended trial wouldn't go amiss? After all, wouldn't want to lose the car trying it

Thanks,

Kevin

[Edited by K9VYN [Kevin W] - 8/19/2002 7:24:05 PM]

EvilBevel

It doesn't IMHO. It's one of the little things that help, just as the mech. front diff, but I think we both know we need another centre diff

Mind you, it would probably scare me to death as I'm a **** driver, but it may just be the reason why power on oversteer isn't easy in a Scoob, UK or STi.

EvilBevel

Non expert disclaimer still counts, but I'd think that's not right.

Try putting 40 psi and bald tyres at the back. THAT would make you oversteer

And before you think I'm nuts... I've seen this done by oversteer junkies with great success, even on a surface like Elvington's

K9VYN [Kevin W]

Evil,

So what do you suggest I go for to get the most neutral (best of both/all worlds) handling?

Cheers,

Kev

carl

Surely the optimum handling would be achieved with the roll centre located at the centre of mass, hence lowest moment of inertia around the roll axis?

Mycroft

Andy F
I run SusP3 have you the info to hand as Macphersons are not easy without a computer programme, just need Strut HEAD inclination and centre plate height, at rest angle for lower links and there offset from centre for the chassis connection and some likely cambers, and for the front the Inclined angle and castor angle, I can then run it in 3D, if you havent this facility.

EvilBevel

Kevin, I'm in no position (read: crap driver) to give suggestions, but I did understand somewhat that the holy grail in handling doesn't exist. In fact, a totally neutral car could be a nightmare given the right conditions.

Understeer or oversteer biased cars do give you a starting position (you know it will do *this* when you do *that*), neutral cars stay, well, very neutral until you overdo it/make a mistake. Understeer = very safe (most of the time, not talking about lift off oversteer etc), oversteer is more fun when you are up to it (mostly on track/country roads) or have the skills, and is, despite all the hoopla in this thread, ultimately faster. But it all depends what kind of driving you do, skill level, and possibly even adrenaline level.

Apart from that, it's a very personal thing really (unless you are a racing driver looking for the last 10th's of a second, and probably even then...). I would *love* a bit more oversteer without having to trail brake/left foot brake/lift off like a fool, but at the same time the understeery character of the Scoob probably saved my life a few times ("ooooh, shiiiite" moments)

Despite all the big words in this thread (and I'm sure even Simon agrees with this), it's about how you feel your car should handle, about how happy you are with it (maybe before you go to the next stage of "handling" even).

I have to lie down now