Juha G

I would fix the suspension geometry before trying anything else.
If you look at the graphs Bill posted above you can see that at stock -60mm your front suspension geometry is far from ideal... look at the red toe curve; when your front wheel moves up the toe in first increases and the all of a sudden it starts decreasing.

here's a good read: https://www.google.fi/amp/www.hotrod.com/articles/ctrp-1001-bump-steer-explained/amp/

Rancie

Thank you for taking the trouble to send me the link, it was interesting reading. I have been lucky enough to drive for a UK race car manufacturer and experienced the effects of bump steer first hand during the development of new chassis. My 964 does not display the tell tale traits of bump steer. In my experience, it's less of an issue in general in 911's because in the critical cornering phases of turn in to apex, the nose is often 'nailed' to the tarmac via a trail, reducing front suspension travel to a minimum.

Now that the Elephant sport bushing and Tarret spring plates have been delivered I will get them fitted and shake the car down on a test. The result will either help to isolate the problem or remove it entirely.

I may also look at replacing the steering rack bushing.

Will report back

Juha G

Understood. I am basing my comments solely on the theory and unlike you I am a true amateur (not a very good/fast one either) so considering your background I think you are in a much better position to evaluate what is happening in your car.

My only hands on experience with this is my 993 "RSR" creation, which when I bought it was riding way too low and with C2 uprights. It handled terribly.
I raised it to about RS height and changed to RS uprights and it was a night and day difference.
My other 993 (which is being converted into a GT2) came with the right stuff when I bought it.

Even though bump steer is not your issue, it could be that have done other changes (too stiff springs etc.) to eliminate it that result in the behaviour you are experiencing. I don't know, I'm not an expert.

Please do report back if you are able to cure the problem with the bushes etc. It is a very interesting subject.

Spyerx

I do think spring plates and rear solid bush on the swing arm are critical for you. Have to get that back end to be predictable and with all the rubber it's not. I felt my car stock was like driving a wet noodle. Now it feels like a smaller less powerful version of my 997rs :-) and I like thwt.

Regarding the club sports. I'm not super impressed by the stock setup. I feel the spring rates are too high for dual purpose and the splits too great front rear. Also we went to a helper not a tender for reason below. We lowered the rear rate and upped the front to about a 150lb split. Also the front shock bodies are too long and kw is addressing this. It limits travel with aggressive alignments. Rears are ok.

Feel on the damper is decent. My ohlins single adjust feel substantially more supple but it is on a different car.

Overall I'd say the dampers are a good value and pretty good, decent control, but out of box kit is not perfect, but I would love an ohlin on the car... :-)

Rancie

Impeccable taste. The 993RSR is one of my all time favourite 911's!

Rancie

'Like driving a wet noodle' - brilliant!!

I agree regarding the KW's - not perfect but good value for money. I specked them because they share the same valving set up and the competition units but fitted in the budget range that I set for the car.

Interestingly, I originally saw my 964 as a little 'hooner' that would sit towards the 'not that important' element of 911's that I have driven. How wrong could I be? This little car is one one the very best road cars that I've ever driven and I cannot be parted from it. The only car that beats it for feel and engagement is a 996GT3RS and that is probably the very best road registered car that I have ever driven.

If I had known how good the 964 was when I bought the car I would have specced JRZ pro dampers. The car is that good - it would have been money well spent. On saying that I am quite happy with the KW option.

I will be interested to know if you stay with yours or upgrade at some point in the future?

porsche mania

The front end on mine is sorted now since the last lot of upgrades. Before upgrading the uprights, suspension, inner and outer track arms along with corner weighting an alignment. I was at rs height before with cup shocks and rs progressive springs and while the car felt OK it wasn't consistent and was holding me back from improving, tyre wear on ths front now sbows much less understeer as well.The car is now at rs -20mm and is the same lap after lap. Just need to sort the rear end now which I'm nearly positive is the trailing arm and spring plate bushes. I put the improvement on the front down to a combination of all the upgrades/setup but am positive the main issue with my old setup was way too much suspension movement with the rs springs. While the car still lapped fairly fast it was unpredictable, I'm sure the issues could be driven around by someone who has more skill than me but I have improved more in the last summers track driving, since the mods, than in the 3 years before it!
I'm happy to share some alignment settings if you wanted to compare. Out of curiosity what tyre pressures do you run in your car and what weight springs do the kw's come with? Jim.

Rancie

Hi Jim. I run my cup 2's at 32. On a clockwise circuit my starting pressures cold are 1.8 bar front and rear on the loaded side and 1.85 on the less loaded. They come up to pressure in 2 laps - tyres go off in 5. The original cups were much more consistent. Spring rates are 340 front and 685 rear. I run - 2.75-3.0 deg neg on the front and 3.0 on the rear. If I were running slicks I'd run -4. Max caster, 5 min toe out on the front and 10 on the rear. I also run a lot of rake - it helps drop the nose quickly.

jevvy964

Good to see you on here Steve, much better 964 tech knowledge than the other channel. Sounds like you have bonded with that little red rocket, make sure you dont make it too antisocial for road use otherwise it'll end up at the back of the garage other than trackday outings.

I think you are heading to Oulton again this year, are you taking the red car? I'll try to find you to say hi this year instead of just exchanging nods in the pits

I think we were at the Snett day you posted the vid from earlier in the thread, you were parked up towards the very left of the pits beyond the garages as I remember? Did a quick mashup of our laps, you clearly carry way more corner speed but the slightly better power/weight of my car balances it out a bit.

http://vmashup.com/0uZcn4om

(Sometimes have to refresh a few times to get the vids to start at the same time and a dab of pause on either vids when we hit traffic keeps them roughly in sync.)

Rancie

Hi Jevvy thank you for posting, I found that interesting. Nice neat driving. I'd like to view your link separately to compare tyre squeal. What is your car spec and set up? Even with 3 deg neg my rear loaded tyre had wear signs an inch up the sidewall which showed the extent of the movement in the bushing.

Will be at Oulton in the 964 if the diff arrives and is fitted in time - if not I'll be in the 997 cup which would not be my ideal first choice for that event - I have no wish to terrorise everybody there. It would be nice to say hello.

Yep that was me at Snett, it was the first outing of the car. Only changed since then have been harnessess and a remap. I absolutely agree about leaving some comfort/practicality on the table. The bushing/spring plate and diff upgrades will be the last of the chassis mods for me. See you at Oulton

jevvy964

Here is the direct link to that vid:

There are a few more on YT from that day. That mashup tool is handy for comparing different cars or same car different laps.

My car is an 88 impact bumper (torsion bar) 911 but with a 993 engine running about 290bhp. I have standard front torsion bars and slightly heavier rear bars and boggo standard sport bilstein shocks all round with fairly aggressive geo and R888's:



I'll come and find you, me and my Mrs will be sharing her 964 so if you see us first say Hi:

-nick

Just to clarify and not add to the confusion, positive ride height on Bill's plots represent decreasing height. The -60 height is 60mm in the rebound direction, above the static ride height. Plots made by engineers

The bump-steer gets dramatic when the toe line is more horizontal. Which happens at lowered ride heights (the upper half of the plot).

Juha G

Thank you for the clarification! So it is even worse that way around. I did wonder why it says "decreasing"...now I know!

So at stock -60mm rideheight your toe changes a LOT when the suspension travels up and down. Far from ideal.

Rancie

Both cars look lovely. Look forward to meeting up at Oulton

Rancie

Thanks for Clarifying Nick.

The graph shows - if i'm reading it right - that it is mainly toe changes that are pronounced during suspension travel. As a driver, I would prefer to drive around toe changes rather than camber changes (within reason). The rear loaded tyre on the car (clockwise circuit) is showing signs of wear over an inch below the tread level on the outer shoulder. That is implying substantial geomtery deflection under load.

From my perspective, I think that the elephant in the room is coming from the rear of the car and not the front. This is supported by the fact that I do not need to go to work from the driver's seat until the car is fully loaded in the corner. If the problem was generated from the front of the car, I would need to go to work much earlier in the cornering phase to work the nose in

The Elephant sport bushes and rose jointed sprint plates will go a long way to tie the rear end down. Once they are fitted, I'm looking forward to driving the car on the circuit to see how this translates into the handling. I will make sure that I get some in car footage so that i can share it with you Chaps