Ruairidh

I want to, just work is interfering with all my fun right now

Still, in this economy, I'm not complaining (well not much)

DJF1

I will chime in here, having experiemented a bit on the rates, adjustments etc... Its a great PITA to get it decent although I must admit lately that I have given up on the notion of having a riding on rails track car. I realized, hey I actually do drive a 911, neutral handling may never down up on us! Something strange that happened on my last race... I shared my car with another hotshoe Rennlister and we both kind of gotten surprised by one thing. When you actually have the car on the absolute edge, we are talking about slipping and sliding on every turn, one characteristic came out. Initial understeer which after the apex turned into oversteer!!!!! How about that??? Here you are turn 4 at Putnam a fast right hander diving towards the apex the nose fights for traction, understeers, you are on throttle and all of a sudden the tail steps out...Almost every corner was like that at least the ones that your heart could take the constant feeling on being on the absolute ragged edge...
I spoke to my mechanic who has been racing and fixing 911's for over 30 years and he said that if you actually go fast and the car is setup right this should be the way it handles!!! As a matter of fact he said that due to the short chassis the RSR's have this phenomenon more pronounced and when they were racing they had a lot of understeer problems...Now I have not driven an RSR but if my car's handling is an indication then it should not be far off...
So maybe this quest of the perfecty balanced 911 is a mirage after all... what the hell though you get such a high trying to master the beast that is called 911!!!

JohnM

Hi Danny,

That understeer on entry/oversteer on exit is, as your mechanic says, normal - it's actually 'just' physics, due to the reaction forces of the yaw rate you generate when winding lock on on corner entry (reaction force is greater at front than rear) and unwinding it on corner exit (reaction force is greater at rear than front). You can actually vary the effect by how fast you turn the wheel, try unwinding really quickly on exit some time if you want a serious dose of oversteer or crank it on really quickly on entry for that tires on fire, bye-bye apex, snow plough effect

Paul Frere explains it nicely in his Sports Car and Competition Driving book.

Edit: and a PS, if you don't have a little inherent understeer in the setup there will be no rear grip reserve to use to accelerate you out of the corner on exit when you're on the limit...

DJF1

I knew I should have paid more attention to my physics class in school Proffessor M!

Fun aside, while it does make kind of a weird sence in a way, your brain gets totally confused when it happens.. Imagine if you lift what effect that yaw rate of yours ill have to finding the apex

BGLeduc

Roger that.

One thing I was taught in the Evolution autocross schools, but perhaps never was able to put into pracice, was that, in a severe understeer situation, you want to unwind the wheel as you exit the corner.

Lets see, I am trying to get around a corner, I have the wheel turned, and due to understeer (and perhaps being a bit hot on corner entry) the arc I am taking is bigger than I would like, those I am drifting wide.

You want me to turn the wheel in the direction I DONT WANT TO GO?!?!?!?

Sorry, but my brain has a real hard time with that!

BGL

Doug H

I like the Ruf. Very driveable, not too stiff. I expected the car to ride a lot stiffer when I first saw it. The car, however, handles very nicley. I drove an RS America recently that was only driven on the track by the owner. Even though his suspension felt much stiffer and rougher when driving in a straight line, my car felt like it handled curves as well. My also car has wider rubber if that would make difference in grip.

The owner paid $ 2,695.00 for my Ruf kit in August of 2000 which included front struts, rear shocks, springs and swaybars and without installation. Any ideas what the Ruf kit sells for today. Just curious.

Cupcar

I have the H&R Supercup kit which has very nice Bilstein shock hardware consisting of RSR/Cup style front struts with the huge piston rod that is almost the diameter of the strut itself and aluminum rear shocks with a monoball lower mount. I'm not sure you can get these shock parts from Bilstein directly-I think it's either H&R or Porsche Motorsport as suppliers, I could be wrong (not the first time for that!). I think the next step up from this H&R kit is Moton or other $$$$ set up as far as shock quality.

The upper monoball mounts the kit comes with are a little sketch however. The rears did not fit without machining and the fronts would work fine in a wide body applcation but do not give any more negative camber in the front than the stock RS units do. I had to make new mounting plates to get what I wanted.

The springs and other associated hardware is first rate quality though and the springs are standard H&R racing parts that can be easily changed if other rates are desired.

The spring system is a helper spring/main spring set up. The rates (pounds/inch) are:
Front: helper 140/main 457
Rear: helper 226/main 685

The helpers are compressed fully at rest so only come into play when shocks extend beyond the length at ride height. I like the way my car handles with this kit better than the original RS springs and shocks my car came with. I think perhaps these rates may be about as high as one can go without adding a roll cage to stiffen the car.

Adrian

Do we have any EIBACH spring experts here. I have an Eibach spring
EIBACH 20/96 343950 RS/F
Does anyone have any idea where this spring originated from. I have searched high and low and cannot find anything apart from Eibach USA denying it is their spring.
Ciao,
Adrian
964C4

joey bagadonuts

Thanks, again, to everyone for your contributions and perspective. As I researched the issue further, I came across this exclellent white paper which outines the effects on handling that result from shock valving changes.

In case you don't have the time or interest to give it a read, I'll save you a few minutes. The bottom line is that it's always a compromise. If you set up the car to oversteer more on turn in, you may get more UNDERSTEER as you exit the corner. And, as Danny and JohnM pointed out, the converse of that would be true as well.

JohnM

Just to add to the oversteer/understeer confusion, in a car which is neutral (i.e. equal slip angles front and rear under constant cornering) the actual cornering balance will depend on throttle input, but not quite as straightforwardly as you might think.

As drive is increased from none (i.e. from constant speed, neither accelerating nor decelerating, NOT from no throttle), a RWD car first gains increasing understeer, before reaching a peak of understeer which then reduces as drive is increased further, until it eventually goes back through neutral and into oversteer - the oversteer part of this curve gets pretty steep as throttle input is increased.

The upshot of that is if you are finding the car is understeering, adding just a little more power can make it worse, but pushing through that and adding even more power balances things up and you get back to a neutral balance. Being confident with the throttle can pay big dividends in cornering balance.

It's important to realise how much influence the driver input has on the car's balance and not think that some magical spring/damper configuration will deliver a car that is neutral whatever you do with it.

Jeff Curtis

Well said!!

I can name some turns and some tracks where that advice really pays out.

When you PLOUGH through a turn, and be patient or constant with the throttle (after learning that giving it more or less does NOT help) you can really pull out of it with the gas pedal after apex.

Good stuff.

Dennis Kline

This has been a great discussion. I am a novice at discussion forums, but I've been around racing Porsches since the 1960's when we used to design suspensions around the natural frequency of the suspension, ala Len Terry and Colin Chapman. If anyone is still listening, I would just like to note that Cupcar's comments reflect the PAG designs for the race cars of the 70's. The factory springs that I am familiar with, were designed so that they were linear in compression and degressive (? opposite of progressive?) on rebound. The springs were wound with tapered wire so that the degressive (still doesn't sound like the right word) portion was bound up at the static ride height. As I recall, this wasn't for comfort, it was intended to reduce the amount of roll and suspension changes during cornering.
dk
964 C2

forklift

I think this is the tread that Erick was referring to. I think I am going to print it out and read it on the couch....and then read it again, because right now my head is spinning (partly because it is 4 am). Once again I find out how much I don't know......I did order "How to make your Porsche handle" by Fred Puhn a few days ago, so hopefully that will help (as well as Adrian's book for specs).

Jeff says not to get a "turnkey", but someone else (who wants to remain anonymous) here told me to get the factory Carrera Cup, because it was designed specifically for the 964. I am not trying to start an argument, it is just difficult with all of the opinions. My mechanic thought the Carrera Cup is the next best thing to the H&R Supercups, which are probably overkill (but I guess you can never have too much power or have you car handle to well). I am still concerned with the sway bars at 24/18, when my M030s USA are 22/20. Should be interesting, especially when Jeff wrote, "You see, for those of you who are running a 24mm (RS) sway bar up front, with 19mm-21mm in the rear, BUT have one of the "sporty" spring/shock combos, not a racing setup - are effectively using your sway bars to stiffen up your spring setup. I went that route for quite awhile, before realizing what was happening with understeer and all...then the SNAP!!".....but I assume the factory knew what is was doing and always read great reviews of the Euro RS suspension (except ride).

Excuse me I need an aspirin now.....

Jim

forklift

P.S. I run 255 rears and 235 fronts on my track tires (032Rs) w/ some front rubbing, which with the current set up works well. My street tires are 255/205 (S-01s), which I know are the stock sizes, but since I got my car with the 235s and I have not even mounted my street tires, I don't know how much differently the car will handle with the different sizes (my street wheels came w/ 205s mounted).

So my question here is; should my track and street tires be the same width?, both are 17s. Of course when I get my new suspension, I will have it corner balanced with my track wheels/tires.

Sorry for all the questions and thanks! Hopefully I will be able to answer some for somebody someday.

joey bagadonuts

Jim,

I think you're fine with your current sizes. If you plan to use your street tires as track "rain tires" you may want to match the race compound sizes but for street use only--where you're not really pushing it--there's no need to buy new tires.

BTW, here's what I went with: Factory RS Coilovers with Monoballs.

I've only driven my car a couple times since the upgrade but, compared to the 80K-mile Boges, the difference is remarkable. The car feels glued to the pavement and the springs rates (progressive 308F/508R) are very streetable. The monoballs have not introduced extra noise, but my car was already a bit loud with cat bypass and g-pipe, so I'm not a good judge on that issue.

I won't be able to give the track update for a few months, but I'm sure the difference will be night and day. The firmer rates at the rear should add some tossability (former Eibach's were 250F/256R) and the stiffer rebound will transform cornering capability. Can't wait.