Spiffyjiff

sorry if it's a stupid question but the more i modify my car, the more fine tuning i need to learn about.

in a general sense, i believe dialing out push can be accomplished with loosening front (anti-)sways or tightening rears, just as dialing out looseness can be accomplished with the opposite tweaks, correct? however, can ride height adjustments accomplish the same effect? (i.e. will raising the rear help dial out push? or raising front help dial out looseness?)

for discussion sake, assume bump steer and detrimental camber changes are not an issue. i'm curious specifically what ride height adjustments do for grip/performance.

thanks all...

997gt3north

I'm about to comment on a topic that I have no knowledge so I'm just going to repeat what a professional driver said to me about car setup and my car. He stated that 'he' would drop the ride height of the rear of my car to transfer more weight over the rear axle to increase grip during trackout - to be faster - this is how he likes to setup cupcars - i.e. faster for trackout - more weight in the rear. This is a clearly very complex issue with so many factors coming into play (I'm just repeating what he said). His style was to set the car up for push (stiff front, soft rear, max grip in the rear) so he could trail brake aggressively on entry (passing people / rotating the car) and then with soft rear and max weight over rear axle for grip so he could get on gas as early as possible - he stated this was the fastest way to setup the car.

So, to address your question, his comments would imply that dropping the rear ride height has a 'similar' effect to softening the rear bar.

I'm just relying the info - I'm sure this an incredibly complex situation that involves many many variables.

Seth Thomas

This is the real answer to the question. Too many variables to give a concrete answer. Yes ride height can be used to tune the car but you have to be real careful adjusting it for the right reason or it can really come back to bite you. Ride height is not the same as going a hole softer or stiffer on a bar. It can change balance in a big way.

savyboy

Ride height change on one end of the car is going to affect rake, don't change it unless you have a very good reason to.

Change your understeer/oversteer with:

Driving style
Sways
Spring Rate
Damping

Depending on where you are trying to change the car, ie- turn-in, steady state, track out, etc will determine which variable you should change.

spare tire

I think what every one is trying to say is that, yes , ride height can change or increase grip but along with the change comes alot of side effects and everything is interrelated. A better way to ask your question would be; My ride height is xx front left, camber -x, toe is -x, corner weight is x, caster is x, front track is xx, rear track is xx. Wheelbase is?
the tires I am using are Michoosistones and list the whole set-up for all four wheels including hot pressures. Then explain what negative thing the car is doing and when it is doing it. High speed left corners? PUSH Trailbraking into hairpins? rear comes around. Then ask what can be done to attempt to solve? or I am thinking of lowering driverside front 2 mm. Will this solve my problem?

Get a good set up from a race shop and then play with your sway bars. I think most rennlisters do not have the the answer to the exact set-up of each wheel as outlined above. I didn't even ask about what the settings are on your tripple adjustable JRZs.

Seth said it best.

MGR-GT3

We all know that a ride height adjustment (front or rear) will affect the handling of the car ALL the time, not just during cornering, especially as it affects the rake and front/rear weight distribution. Swaybars however, ONLY come into effect during cornering -unless you set them up with a certain pre-load.

Stockcars (cup cars) usually refer to "lowering the rear" when they make track bar adjustments. They don't change the actual ride height as much as they change the roll center via panhard bar or Watts Link. A lower roll center, will allow a stockcar (solid axle and no independent rear suspension) to have more traction out of the corners at the expense of being tighter on entry. As with every suspension adjustment, there's a point of diminishing return in which too much of a good thing, actually becomes a negative.

In general, I wouldn't mess with the ride height once you have corner balanced your car and achieved the numbers and rake that you want. Like savyboy said, spring rates, shocks, wedge adjustments and also tire pressures will be your first options to fine-tune your handling.

Suspension tuning is part of the fun!

MGR

Spiffyjiff

i have an 06C2S with bilstein damptronics, TPC sway bars. 600#/800# springs front/rear. what i know (in degrees unless otherwise specified):

FRONT
camber -1.78 -1.75
cross camber -0.02
toe -0.9mm -0.9mm
total toe -1.8mm

REAR
camber -2.26 -2.37
cross camber 0.11
toe 1.6mm 1.7mm
total toe 3.3mm

i dont believe my caster is adjustable. and since i have my original LCA's, they are not adj either so i am at my camber limit in front.

the bilsteins are not as adjustable as i'd like - now with heavier springs up front, the car naturally does not sag as much and i am now at the bottom of my height adj threads up there. from the ground to middle fender is about 26" in front and only slightly higher than that in back. i havent yet measured the official way (and just how do i do that, again...?) but by simply looking the profile and from seeing others at the track, i can tell you that mine bascially has little or no rake, as set up by my indy.

i use 888's on track, starting at 26psi cold, and usu end up no more than 36 hot all the way around.

in a nutshell, after spring change (up from 350/550), tire wear was fine and turn-in was fine but the damn mid corner push was a BEAST - my original sway positions were front, 1 away from full hard (5 positions) and rear, 1 away from full soft (4 pos) and my indy left them unchanged when upping my springs. so all of a sudden push was unmanageable. i found the best solution so far is leaving front sway as is, and putting rear at full hard. this way i can rotate car a little better.

sooooo my original reason for posting was, since i cannot lower the front any more and despite preferring not to raise the rear by too much....maybe raising slightly would accomplish my goal of dialing out push and allow me to back off the full hard rear sway?

sorry for the thesis but trying to give all relevant info!

Seth Thomas

You are on the right thought process to get rid of the mid corner push. You can raise the rear very slightly to help dial some of it out. The simple reason this works is that it transfers some static weight from the rear to the front, which helps the front grip and makes the rear loose. This will work well in low to medium speed turns. It will work in med to high speed turns too but I have had it make the rear too loose for these type of turns.

With your current setup you can try to raise the rear to see what the reaction of the car is. It doesn't hurt to try it but don't raise it more than 1 full turn at a time (1 full turn is a big change). Note what happens and see if it works for you and your driving style.

Also something else for you to think about. What are you doing with your right foot when you start to experience the push? Is your right foot touching the throttle pedal? Is it applying any throttle at all to the car? If you are applying the slightest bit of throttle before the apex and the car is pushing apex out then it is a throttle induced understeer. The change in ride height will not help you remedy what your right foot is doing. The push will will still be there.

savyboy

If I read you correctly, you still can loosen the front sway from 1 from full tight 4 more holes all the way to full loose yes? If so, why have you not done that? It is the obvious answer.

If you have too much mid-corner push, loosen the front sway and leave the rear full tight and see exactly what you have to work with? If you now have a drift car (doubtful) then back off the rear one hole at a time to find your sweet spot.

My perception, and I might be wrong, is that TPC loves cars that push. If that TPC front sway is too stiff (you still can't dial out the push with full tight rear/full loose front), then take it out, replace the OE bar, and try to dial your handling with only the rear bar.

You have done a lot of tweaking and it is tough to guess just where the heck you need to be even with the info you provided. But, loosen the front sway man!

AudiOn19s

Spiffy - Do you have heights from before / after the spring change?

Are you saying you think you lost rake that you might have previously had during that spring swap leading to the understeer issue?

Here's how you measure ride height correctly: and height ( rake ) figures for MKI and MKII GT3's. Not sure where 997 info might be found.
https://rennlist.com/forums/996-gt2-...-to-check.html

Here's a thread I started recently inquiring about rake as well
https://rennlist.com/forums/996-gt2-...de-height.html

997gt3north

Few thoughts

1) lower front hot tire temps to 31-32 - leave the rear at 36
2) you didn't say what size tires you are using 18/19? - if 18s, make sure you are using the 255 front R888 to max front grip
3) after you do 1&2, you are going to have to next soften the front sway until you get what you like, and/or reduce the Rear camber to -1.7
4) get those gt3 front lower control arms or similar and get front camber to -2.4

Another important question
- did you have your shocks re-valved for these spring rates or is this just a TPC spring rate increase without re-valve?
- if no to revalve, how does the front feel given the big increase?
- if you can't lower the front, is this because the front spring is too long given the rate increase? - if so, shorten it by 1 inch


As Seth said, if you push is from the throttle (sounds like it), ride height really isn't going to cut it so soften the front bar by 1 hole to it's softest setting.

This type of TPC 'push setup' is preferred by many cup drivers as they use a lot of trail braking to rotate the car on entry and want a slightly pushing car on exit - but they aren't camber restricted as you are in the front and they have sway bar flexibility that you are currently almost out of. If the softest front hole + slightly reduced rear camber + slightly lower front hot psi temps doesn't work, the easy answer is to put the stock front bar back in.

Spiffyjiff

nope, i take foot off the pedal, open the wheel (within track pavement limit, of course) when i start to push. i learned that lesson quickly in autocross a few years ago - i became quicker thru the turns by going "slower" than when i was an idiot, plowing off course at full speed!

i have 5 pos in the front, and am one away from full hard now. so i have 3 more in which to loosen.

interesting you bring that up - i'm not sure if TPC likes push but they did advise to leave the front sway alone. however i have to say, i kind of agree with them. i def understand what youre saying but i also hate body roll/like a very firm front. so am i crazy or can i really feel the extra body roll induced by loosening the front sway, even one hole? i.e. i have tried backing it off one or 2 holes for a session and maybe it's all mental, but i seem to remember feeling more roll-y.

no, unfortunately i do not have heights before the change. but since i'm pretty sure the rear is the same height as before the change, i am assuming logically (as well as it's visually noticeable) the rake is almost gone due to the stiffer front springs/less sag.

Spiffyjiff

yes, i was thinking about playing with tire temps front to back but i've heard that while fine in autocross/lower speeds, it's not advisable on the track/high spd. thoughts?

am using 19" in stock width.

i just HATE losing firmness up front but maybe youre right, maybe i do have to loosen the front as opposed to tightening the rear.

yes, the fronts are revalved for heavier springs. and yes, the 8" spring and almost zero sag add up to no threads left in which to lower up front. as a matter of fact, indy even took off the front lock rings to get an extra 1/4" or so. i have thought about swapping for 7" but i have heard that the longer the spring = the better it performs??

997gt3north

At that spring rate you need a 7" spring - that is a cheap fix that I would do.

I have run the 235/305 19" R888s (not my favorite tire) but that front tire is a wide 235 - measures as a 250 so that even further highlights your issue. Definitely run the front tire at 31 hot - it is fine - I have done it at many tracks with that tire - it will work at 31.

My own experience with my 997gt3 mk1 is that a few simple changes should fix your problem.
1) if you aren't going to get more front camber, you have to reduce the rear
2) keep front temps at 31 (lower than rear)
3) get your sways working to fix 95% of your problem - if the softest front setting doesn't work, either remove the beefed up front bar or get a thicker rear bar - address this issue first
4) I personally would get the proper rake back to the car by getting the front lower - better aero, lowers CG, restores what the factory thinks works best

AudiOn19s

There's alot of great suggestions here to make the car work like you want, however if your hunch is that the rake was effected by the current height of the front due to that 8" front spring that's where I would start then work through the rest of the suggestions until you find the car's sweet spot

1) check heights, fix rake if it's not at least to OEM specs (with all the mods to your car maybe OEM 997.1 GT3 specs?). - fix could be to raise the rear or get a shorter spring for the front

2) Adjust front tire pressure

3) Adjust front sway bar

**all of the above can be done with what you've already got unless you decide to go with shorter front springs

Then you need to throw parts and $$$ at it from there.

-Front camber solution

-larger front tires

...knowing the way most of us work you'll probably end up with all of the above and the thing should stick like glue then!

Andy