Protocav

Why is the front ride height higher than stock?

Red Bear

Just my personal preference but drive the car hard with the understeer and it will move to overstreer at the end of the tire cycle.

zanwar

I left the setup in their hands so I don't know the specifics. Perhaps they couldn't hit the other numbers without the front ride height set at this level. I know they tried various combinations of ride height and settled on this one for now. I'll post the other numbers when I have a chance.

997gt3north

There is a lot of very good information in these two messages from these two very fast advanced drivers.

It sounds like you are at the beginning of your track driving journey. You have put a part into your car that is designed to be exploited by experienced drivers and also during race type situations.

When Randy says, "learn to re-drive the car", what he is means is that there is a way to make it work around the track, but with your current style and experience you are not currently driving it in a way that works. When Grady says, "drive the car hard with understeer", if you knew how fast Grady is, than that is quite the statement and further highlights the nature of the problem you are facing given your experience level.

Driving a GT3 'hard' isn't that easy to do - it takes a lot of experience. What both Randy and Grady are saying is the same thing - but they have the skill to do it - beginners do not. That said, you can try and apply what they are saying. They are trying to highlight a few things like trail braking, more aggressive corner entry to rotate the car, getting on the throttle harder once the nose is set to get additional rotation. This all sounds like it is doable and easy - it is and it isn't - all depends on your skill, the track, your comfort level with running off the track, the grip level of your tires, etc.

I think it is great that you are on PSS and not sticker tires as you would just get into trouble faster until your skill level has improved.

All things being equal, when you put in the cup dif, 'you' are likely going to need more rear bar to help with rotation (things like more front camber, more front tire, less rear camber, more front toe out, less rear toe in, etc) can and do also help - but the biggest thing you are going to have to do is try and apply what Randy and Grady have said:

1) you will have to be more aggressive on entry under trail braking to get the car rotated and then get the nose of the car properly set (re-learn to drive the car) - you can't just snap off the brake, mash the throttle as the nose lifts and expect it to work
2) with a car set up for understeer you will have to (drive the car hard) - this is the mental approach that Grady is trying to get you to think about - an understeering car has to be more manhandled to get it to work - in someways this is a comforting thing in that the car is setup in such a way that it is overly stable and you really have to be aggressive - and the car will reward you and it won't snap rotate on you while you are doing this
3) (re-learn to drive and adjust the bars) - you massively changed the diff from OE specs so you have to expect that the bars will need changed - most likely more rear is the answer


As an example, I have a Guard diff set up at 50/80 lock - which is more lock than yours but it has less pre-load - so it likely isn't that far from your spec but this is what I have done
- I upped the factory OE gt3.mk1 bar to the GT2 bar
- run .5 degrees more front camber than rear
- learn to drive the car with lots of trail braking and getting the nose set before throttle application
- aggressive throttle at the apex
- more front tire

I've had the above car driven by a real pro and he loved the car as it still worked for him as he could be so aggressive (like Grady was saying) and it worked. It works for me but I still have to think 'more aggressive' when I drive it.

Besides removing the diff there are some things you can do as were mentioned by others but the cup diff is set up to allow a pro level driver to be very aggressive in the car and for the car to perform under that scenario.

You are basically using a small headed extra stiff men's tennis racket or a forged blade with X200 shafts in golf terms - if you don't hit the sweet spot and take a rip at it - it isn't designed to work - that is what you are feeling.


Look at it this way - you can grow into your car - and there are small things you can do along the way to make it work better while your skill level goes up.

sraz786

Excellent feedback, thank you all for your responses.

It seems like I'm able to answer my question of "is this normal for the Cup Car diff" and it sounds like the answer is yes. With that being said, my current skill level will not allow me to exploit the advantages offered by a cup car diff. Sounds like I have some "driver" mods which need to be made by taking proper instruction.

Ur20v

Bingo!

CRex

Tons of wisdom in this thread from people who REALLY know these cars. Redbear and 997north's comments particularly resonate with me. These cars have a big "hump" that new drivers have to initially get over, and once that's clear you'd be amazed at the cars' near-telepathic abilities.

Ride that understeer, observe grip changes throughout the tire lifecycle. Pay special attention to weight transfer which affects these cars FAR more than MR/FF platforms. 997s categorically lack mechanical front grip, which deficit turns up twice as bad if you butcher the throttle and abruptly shift weight rearwards mid-corner. Extending your trailbraking by as little 0.1 sec and delaying the opening of the throttle by that same 0.1 sec can make all the difference. And sometimes that's enough to change your perception from "bad understeer" to "wow I just aced that corner".

Enjoy the car in safety!

zanwar

My take away from the experience is that installing an aggressive component like a cup car diff needs to be balanced with changes to the rest of the car for it to work properly.

10 GT3

Bushing rotation changes more than caster. Remember that the track arm mounts to the bushing, so changing the rotation changes the entire front geometry. Whenever I see someone complaining about front bite and having their track arm mounted on the center hole in the control arm, you can see the issue immediately. After having the changes to the bushings made, I lost caster (.5 degree) and and gained some camber (.2 degree) with the changes, yet turn-in was incredibly sharpened and front bite improved dramatically. With similar changes to the rear, the rear tracked a lot better and balance shifted from understeer to slightly loose, hence I adjusted my sway bars at the track to get the car back to neutral (my preferred balance). Having this done is a tremendous difference if feel, turn-in and bite of front and and much smooth tracking on power coming out of corners. Tire wear improved dramatically getting at least 20% longer wear out of a set of tires at the track as the tires can work more effectively. Alignment settings are really irrelevant until you have this change done.

My current alignment settings are:

Front camber -3.0 (was -2.8 before bushing rotation)
Front caster 7.5 degrees (was 8.0 before bushing rotation)
Front toe -.01
Rear camber -1.6 (was -1.8 before and after rotation, but I had it reduced when the CL recall was performed to improve rear tirewear)
Rear toe .14

Again, these settings are not so important until after getting the control arm bushing rotation change done. I will comment that -2.4 rear camber is really high. Rule of thumb is the more power, the less rear camber to keep more of the tire even with the road surface when exiting a corner. Remember as cornering G's diminish the tires putting power to the surface need to be flatter to the surface to put power down more effectively.

khooni

Thanks 997Gt3north. This is very illustrative and I appreciate the nuggets of genuinely good advice here.

Nick Wong

FYI it's taken me a year to really figure these cars out (and that is with a ton of behind-the-wheel experience). Get the car to the track, and figure it out. No need to rush your development.

Edrtith

The diff allows you to lean on the front end a lot harder.
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zanwar

We just ran new settings. The goal was to try identical left/right balance at the front of the car:

FL 629 FR 629
RL 1109 RR 986

F Toe out 1mm Camber 2.5
R Toe in 4mm Camber 2.5

There is no understeer to speak of. The back is slightly more loose than before, but not excessively so. I did find the car to be darty under braking. I might try zero front toe next.

TurboS

Kristob RS handles like a F Dream, not exaggerating. Passed a ZR 1 quite handily at our little track.....

Liquid911

Thanks for such an informative post, its exactly the advice us young 'uns need to listen to. Just one thing I don't understand re your statement around been aggressive. If I mash the throttle post apex, I just get the front end washing out. Is there a point beyond this where the front end hooks up and the back end starts getting lose?? Hope my question is clear? I'm not sure how being aggressive prevents understeer post apex!