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I just added rs arbs and now the car exhibits slight understeer.l however front tires are wearing right in the sweet spot. The also have started squealing a bit in harder corners which is a first. The rears are dead quiet.
I have 6 adjustment options to neutralize the handling. Soften the front dampers, stiffen the rear dampers, soften the front bar or stiffen the rear bar. Well and then there is tire pressure...
Understeer occurs even after the suspension has settled so I’m planning to work with the bars and tires rather than the dampers. The first goal in my mind is to increase front grip if possible. My first thoughts are lower the front tire pressure and get some solid hot numbers. Next I think I’ll try going full stiff on the rear bar.
All specs below are front/rear
Advan A052 tires 225/17 255/17
36psi 34psi cold
rs seats in the middle holes
pss10 4/7
rs ride height
Front Caster. L3.58. R 3.47
Camber. L-1.37. R -1.19
Toe. L-0.03 R+0.08
Rear camber L1.55. R1.44
Toe. L+0.03. R-0.05
No lsd.
Anyway my general question is how to decide which end of the car to work with. Obviously either end of the car could be adjusted to get more neutral handling but that could result in less grip overall if adjusting the end of the car that’s set up best.
Additionally is it typical to try to increase grip on the end that’s slipping the most and then adjust the front/rear balance? Do you guys have any standard order of operations for increasing grip. Standard for adjusting front rear balance?
Are you on a track? Your cold pressure numbers would be high for what I'd expect.
Big question is when are you sensing under-steer? Entry? Mid-corner? Exit?
Unless something is wrong it is best to work with the end that isn't working vs un-doing the end that is.
Swaybars are a balance. Soften the front bar to give you more front bite. Lower tire pressures also works. Work with pressures when hot- but for me I'm normally in the low 30's hot which is below 30psi cold for the track.
Actually I’m off to the track for the first time tomorrow! Very excited to say the least. Planning on starting with cold pressures at 30 psi and aim for 36 or so hot and go from there.
I trail brake until close to the apex and have not seen understeer- though this is on the street so I’m always on the cautious side. When power comes on at full throttle I see mid and exit understeer.
I’m going in for another alignment check this morning and may reduce camber a bit up front to try to get more grip there. Also will lower tire pressure relative to the rear. If that solves things then great. If not I’ll still be wondering if I should stiffen the rear bar keeping overall roll to a minimum of soften the front. Leaning towards stiffening the rear.
You're on the right track.
Work on the end that's broken first
All 964's exhibit some degree of understeer or what some describe as "numbness" in the front mid corner, I think its related more to the silly stock caster numbers but the path you are on should get you in a better situation. Look into the parts and setup specs for a 964 3.8 RS or RSR and you will find the solution.
Have fun best of luck!
Cole
^^^ Yes. Focus on broken end, then tune with the other end. Also, driving technique. Trailing harder to get rotation, etc.
I prefer a stiffer front end as I don't like it wallowy. I like it tight and flat. Also, you will want to describe where the push is - entry, mid, or exist.
What you change can matter depending where the situation is.
For example, if it's corner exit on throttle then you might stiffen the rear compression a bit to keep the front end settled, or slow down the front rebound.
Think of the car like a level and fulcrum, you are controlling balance front/rear at various points. That makes it easier to understand what to attack and what to fix.
Some examples with adjustable shocks (dual adjust):
+2 rebound on front - mid corner push
+2 compression on front - corner entry push
+1 rebound on rear - little more rotation rear
+2 rear compression - mid corner going to gas to rotate
+2 front compression . Should help turn in
+2 rear compression. For mid corner going to gas to help rotate
+1 rear rebound to help entry rotation
+1 both front and rear bars. For over all translation support
Just a follow up –I took the advice to fix the front end. I lowered the tire pressure in the front and went to -2deg camber, 6/9 clicks on the pss10’s- then went off to Suzuka. The car was very neutral as far as I could tell- at least it’s in the ballpark. I went with 35psi hot front and rear but will try a little lower next time. Tire wear is very even. I have not touched the arbs as of yet.
Best time was 2:49 which I’m told is good for a newbie on the track. We get 30min runs and halfway through my second run the brakes boiled coming into turn 8 so I decided to go straight off into the gravel- then I came into the pits.
Not sure what happened with the brakes as the pads, rotors and fluid are all recent and good quality. The fronts locked up a bit and the car just wasn’t slowing fast enough so seems somethings not up to snuff in the rear. Hopefully it’s just as simple as a little air in the line. 2 pots in the rear. The fronts locking made me wonder if the abs is 100%. I’ve never had Abs before so I’m not familiar with how it’s supposed to feel.
Aside from that it’s really about driver improvement now. One things for sure- I’m hooked on going to the track!
First time track day is Suzuka? Damn! That's like going on your first date with a Victoria's Secret model!
Unless you have track pads you likely faded the pads vs boiled the fluid. The sensation is having a "long brake pedal"- meaning you just have to keep pushing to get the car to slow (but you have a pedal). Having experienced boiling once (and thankfully in a low speed section after a big braking zone) it is a very different experience- there the pedal goes away very suddenly and you have no pedal (and no clean underwear).
Abs will feel like a vibration in the pedal when activating. ABS should prevent locking- so are you sure you are locking a front? If you really are locking a wheel then your ABS maybe isn't functional. Suzuka has some big brake zones so with a stock car and no cooling it is very possible to overheat brakes.
Yeah- I know right. Like your first date is with a supermodel and you have no idea how to make the move...... But in this case I get as many chances as I can afford.
Fact of the matter is I’m probably overusing the brakes however that aside it’s exactly like you said- long pedal but also basically no rear brakes. To be clear braking power is greatly reduced and the fronts did not lock completely but there was tire smoke.
Would that still be indicative of overheating the (rear) pads? The rears are 2 pistons (1990) so that may contribute.Rotors are slotted fwiw. Pads are sport oriented pads.
Best test of abs is find open road and slam the brakes from40 mph or so. You should feel no lockup. May get a little noise and some jerking and pedal feel. If tires lock abs not working right. Rear channel is single, fronts are independent.
On the pads. Inspect them and bleed brakes. Look at the pads and endure at least backing plate thickness. Since you’re in japan endless and project mu are easily available and great options. Use endless rf650 fluid. Pads endless me20 or mx72. I have even seen it at autobacs there.
Well actually I tried that last night and the fronts locked up. Hmmm....
Seems the abs needs attention. Not sure how to proceed there?
The pads are Seido-ya but I can’t remember which compound off hand. Pretty sure I overheated them rather than boiling the fluid. I’ll be changing the fluid anyway as a precaution.
Yes Japan is a great place to run with the 964. Do you get over often?
Well actually I tried that last night and the fronts locked up. Hmmm....
Seems the abs needs attention. Not sure how to proceed there?
The pads are Seido-ya but I can’t remember which compound off hand. Pretty sure I overheated them rather than boiling the fluid. I’ll be changing the fluid anyway as a precaution.
Yes Japan is a great place to run with the 964. Do you get over often?
pete
At least once a year. Have family in kanagawa.
Could be many things. On my car it was the pump locks, had to replace pump. May try to find a specialist, or, pickup one of the c2 abs test sets from rennlist user cajonfan. The only other real tester is a factory Bosch unit.
Any warning light coming on when you lock up the fronts?
Check the obvious first
- 12V supply to ABS module ans ABS pump, specially corroded pins in the connectors
- check your ABS sensors
- check ABS pump for locked pistons
Front calipers are still standard size?
All standard brakes. I stood on the brakes thinking maybe I’m just being to delicate. Result= volumous front tire smoke. Abs definitely not working! I’m ordering a tester from cajonfan because I want to bleed the unit for sure anyway and it will check piston operation. Will check power and relays first. How does one check the sensors?
07-01-2018, 01:13 AM
Sway bar/handling adjustment – front versus rear
