Ive been wracking what passes for my brains trying to come up with something to add to this thread which hasnt already been covered previously. The core subjects of gearboxes, differentials and handling have all been broached with considerable success (primarily by NumbOne), so, rather than attempt to rehash something that has already been done here, I thought Id take a leaf out of Gasmans book and detail a general description of how I go about setting a car up for GT3. However, I havent laid out the process all the way through to tweaking differentials, anti-roll bars, camber and toe. This is about getting the basic balance of the car worked out in a rational way.
There are a few rough principles that I employ and hopefully some of the following might be new ground. At the least, hearing my take on a given facet of tuning may inspire someone else to thinking Thats not right! and posting a response as to where I goofed. So please feel free to spindle, fold and mutilate what Ive written and dont be shy about sticking the knife in. This is only my opinion and, in the words of the song, It aint necessarily so!.
First things first. All of the following is coloured by my driving style, so its best to make that clear from the outset. Im a fully paid up member of both the Slow In, Fast Out and FR/MR clubs. How I take corners, in the main, is to slow down to the ball-park entry speed and position (determined by experience) with steadily increasing brake pressure; pulsing the brakes if I require a more rapid deceleration. Relaxing on the brakes, I then start to make the necessary steering input but enhance the turn-in by a further quick dab on the brakes. Depending on the corner and the general characteristics of the car Im in, I then either accelerate through the apex and exit or coast into the first half of the apex before throttling on. I avoid drift if at all possible and in powerful rear wheel drive cars Im usually counter steering as I exit to keep the tail in line. The latter is largely due to a flaw in my driving that I cant seem to cure, this being that I keep steering inputs on a fraction too long as I accelerate. Controller wise, I use analogue steering but digital accelerator and brakes with gear changes on Auto (I know, I know
what a wimp!). {
No longer an AutoBoxer these days ... huzzar!}.
STAGE 1
When Im beginning to set a car up, my first port of call, after fitting all the required engine, transmission and suspension modifications, is to take it out at stock values on T2 (Super Hard) or Simulation tyres.
The point of this pre-tuning run is to show you where the problems are in the cars handling, so I would recommend turning ASM and TCS off. The tracks I use for this are Grand Valley and Trial Mountain Reverse as I find they give me all the environmental factors I need (smooth, fast sweeping corners; smooth, tight and/or blind corners; uneven surface/variable camber corners; downhill and uphill braking; long and short straights etc).
There are two reasons I like to use T2s or Simulation tyres for this. Firstly, I nearly always race on T2s (most pit stops take too long for you to be able to complete a 15 lap race quicker on soft compound tyres as the time lost in pitting is greater than that gained by the faster lap times). Secondly, the low grip coefficient exposes any weaknesses in the cars handling much better than if you run softer tyres.
STAGE 2
To facilitate testing, I now set the gear box up for the circuit. The parameters I use for this are fairly common to all of us i.e. decent acceleration coupled with attaining a pre-determined top speed, at the red-band, in top gear, at the end of the longest straight.
Because I use the buttons on the D-Pad for accelerating and braking, I will also try and use the gear settings to diminish power-on oversteer (I dont have the delicacy of touch required to apply less than about half throttle, so some big horse-power, no aerodynamics, cars tend to squirm the back end out on me during corner exit). This can mean Im getting less than optimal acceleration in low gears out of corners but its a trade off Im willing to make for the sheer manliness of low TCS values!
How to set the box up has been excellently explained before by NumbOne so all I have to add is that the magnitude of the Final Gear value seems to have a definite impact on the way the car handles.
A low Final combined with a narrow Autoset gives an agile, responsive car and works very well with NA engines and their, generally, wide torque range. A large Final with a broad Autoset appears to reduce, to some extent, the power-on oversteer I mentioned above, especially with enormously powerful turbo engined cars. This may well be because such a set-up tends to allow you to hold a higher gear in a corner whilst the relatively low road speed as you start to apex means that you begin accelerating from lower revs (i.e. away from the power band) and thus are putting less torque through the drive wheels. The fact that the drive gear has to rotate more times for each axle rotation may also smooth out power delivery.
STAGE 3
Now that the gearbox is matched to the track, you can now start to tune the suspension. For me, the single most important element to get right, at the initial point, is the weight loading of the springs. In both absolute terms and in relation to each other, the front and rear spring rates are the foundation upon which everything else stands. Get this right and all the other adjustments are much easier to apply as you can concentrate on modifying the handling rather than masking a bad choice of spring rates.
I work from the (possibly erroneous!) assumption that, when you fit Fully Customised Suspension, the ratio of Front to Rear spring rates it has at default is one which neutrally balances the car when it is at rest. In other words it is showing you where the longitudinal Centre of Gravity lies by having stiffer spring rates at one end, thus indicating where the largest proportion of the weight is. Sadly we dont have the data to calculate the true C of G but it is still useful to know where along the vehicles length is its point of rotation. For most of the race modified FR and MR cars it seems that the front springs are supporting from 52.5 to 53.5% of the weight whereas for 4WDs its nearer 54% (the extra coming from the front differential I would guess). There are a few exceptions to this (for example the Raybrig NSX has 54% of its weight towards the rear) but it seems generally true.
To work this out for the specific car youre working on, simply divide the Front Spring Rate by the total of the Front and Rear Spring Rates.
It is also useful to note what fraction the Rear Spring Rate is compared to the Front e.g. if the Front Rate is 7.6 and the Rear Rate is 6.5 then the Rear is 0.8553 of the Front. You can use this value to maintain the relationship between the Front and Rear Springs by calculating what the Rear Rate should be after youve adjusted the Front. For example, if the ratio is 0.8553 and you set the Front Spring Rate to 12.7 then the Rear should be 10.8 or 10.9 (12.7 x 0.8553 = 10.86).
As the game does not take into account weight reductions when assigning the default spring rates it is important to note what the cars weight is both before and after weight reductions are applied. Using this as a percentage you can then reduce the spring rates accordingly. For example, a TVR Tuscan weighs 1100kg stock and 979kg with a Stage 3 Weight Reduction. This 11% drop in weight can then be applied to the spring rates. Default springs on the Tuscan are 7.6/6.5 so, with less weight being carried, these can be softened to 6.7/5.7 (or 6.8/5.8 if you want to round up rather than down!).
A better way of doing this is to reduce the Front Spring Rate by the noted percentage drop in weight and then calculate the Rear Spring Rate from this by using the ratio of Rear to Front rates worked out earlier.
Having re-rated the springs for the reduced weight, you can now alter the ride height. If it is lowered (and it usually is!) then the Spring Rates need to be stiffened. As a quick fix, for each millimetre you reduce the ride height, you should increase the springs by 0.1kg to compensate for the shortened stroke. In rounder numbers, if the ride height is reduced by 1cm then increase spring rates by 1kg.
A more accurate approach is to use a simple equation to calculate how much stiffer the Springs need to be to give the same resistance to bottoming out. You can do this as follows:
For a given end of the car, multiply together the Cars Weight (W1), Spring Rate (S1) and Ride Height (R1). This will give you a constant. Ill term this number Loading (L) for want of a better name!
When the Ride Height is changed (call the new height R2), you can work out the new required Spring Rate (S2) by:
S2 = L / (R2 x W1)
For example, the Spoon S2000 Race Car has a weight (W1) of 1050, a ride height (R1) of 90 and Spring Rates of Front 14.5, Rear 12.1.
W1 x S1 x R1 for the Front = 1050 x 14.5 x 90 = 1370250
W1 x S1 x R1 for the Rear = 1050 x 12.1 x 90 = 1143450
If the ride height is changed to 80 (R2) then for the Front
S2 = L / (R2 x W1) = 1370250 / (80 x 1050) = 1370250 / 84000 = 16.3
And the Rear
S2 = L / (R2 x W1) = 1143450 / (80 x 1050) = 1143450 / 84000 = 13.6
A thing to note here is that although bottoming out has not been properly implemented in GT3 (a serious flaw in my opinion), slamming the ride height to the bump stops can have an impact on tyre wear. This is because although lateral thrust forces are reduced by a lower ride height, vertical pressure forces between the sprung and unsprung masses are sharpened by shorter, stiffer suspension. The tyre is having to absorb more of the shock imposed by the road surface because the springs dont give as much i.e. they resist the road rather than comply with it. This can be moderated by careful setting of the damper Bound and Rebound but its a compromise between wear and handling (which handling will usually win!).
[As an aside, it is possible to find published real world figures for a cars weight, spring rates and ride height. Certain factors aside, the physics engine for GT3 is quite accurate and using these actual (as opposed to virtual) settings is perfectly plausible].
In a race-bodied car, there is one final thing the springs may need to be adjusted to compensate for, changes in Downforce. If we assume that the Downforce figures in the tuning interface represent a percentage increase in the effective weight and that the stock Spring Rates reflect this, then if the Downforce is changed we have a different weight value to deal with when the car is moving at speed.
In the real world, Downforce obeys the Inverse Square Law i.e. if you double the speed then you get four times the Downforce. Because speed is one thing that is never constant (for long anyhow) in GT3, it would require averaging a large summation equation to arrive at an entirely accurate answer and youd have to recalculate it for every track! However, luckily it is a valid approximation that, over the entirety of a course, a car will produce an average speed that will generate half the maximum Downforce.
To calculate the new Spring Rate (S2) at each end of the car for a given change in Downforce is relatively straightforward. We know the weight (W1) of the car, the change in Downforce (New Value Old Value or (D2 D1)) and the current Spring Rate (S1). The equation to work out S2 is:
(( W1 + ((( D2 D1 ) x W1 ) /2 )) x S1 ) / W1
It might look a bit complicated with so many brackets but basically all its really doing is giving us:
(Downforce Modified Car Weight x Original Spring Rate) / Car Weight
Using the Spoon S2000 Race Car as an example again and assuming we maximise the Front Downforce, the values we have are:
Car Weight (W1) = 1050
Original Downforce (D1) = 0.45
New Downforce (D2) = 0.74
Front Spring Rate (S1) = 16.3
So, S2 is determined as:
((1050 + (((0.74 0.45) x 1050) /2)) x 16.3) / 1050
= ((1050 + ((0.29 x 1050) /2)) x 16.3) / 1050
= ((1050 + 152.25) x 16.3) / 1050
= (1202.25 x 16.3) / 1050
= 18.66
To work out the Rear Spring Rate if the Rear Downforce is changed, then simply plug in the appropriate values.
With ride height and springs adjusted, its time to take her out for a test run. It might be worthwhile to set Bound and Rebound to 1 for some of this testing as practically zero damping can highlight whether the basic front/rear balance is askew. Analyse how she handles and do quite a few laps until youve got the car, the track and your driving matched the ideal is that you can turn in consistent laps (within a tenth of a second or so) as this allows you to more easily assess the effects of changes you subsequently make. If you cant get that level of consistency out of her (and if you can she probably doesnt need any more setting up!) record your average time and move on to the next stage.
STAGE 4
Youve now got baseline figures to work with and can start adjusting the magnitude of the spring rates. Unless something is very obviously wrong (or works against your driving style) dont adjust the relative front/rear ratio yet. There are two approaches you can take here. You can either incrementally increase the spring rates (for instance by half a kilogram a time) or you can do it by high/low searching i.e. initially large changes gradually getting smaller as you home in on the most comfortable value. Its solely a matter of personal preference and the amount of time you want to spend.
Getting this vital stage right can take a fair amount of time as it can be difficult to decide between the conflicting outcomes desired. Speed (not to be confused with lap times) and handling are not entirely mutually exclusive but enhancing one generally impacts negatively on the other.
It is sadly true that whilst harder springs improve responsiveness to steering, braking and acceleration inputs (all Good Things) they actually reduce grip (not at all a Good Thing!). The trick is to find the compromise value that works for you and gives you the fastest consistent lap time. A spring rate is no good if youre not comfortable with it as itll take too much concentration for you to be consistently quick in longer races a blisteringly fast time one lap, followed by an off on the next, is not as fast as two slightly slower laps run clean.
When youve found a rate that seems to work for you (youre cleanly turning in faster average lap times), it is tempting to try and alter the balance of the car during cornering with the ratio of front to rear springs. It can be done, no question about that, but cornering balance is more properly the job of other suspension components.
Setting the springs to balance a car during cornering will have an effect(and more than likely not a good one!) on all other aspects of the cars character, such as acceleration and braking. The problem is that spring rate is an always on type of setting (has an effect all the time) whereas such components as dampers and anti-roll bars have transitional settings (only come into play during the state changes theyre designed for).
So unless you have a real problem with something like uncontrollable power-on oversteer, Id suggest leaving the relative spring weights more or less alone. Experimenting with small variations will probably do no harm but radical shifts in the relationship between front and rear (such as making the rear rate higher than the front in an FR car) may well mean that youre fighting against the basic chassis geometry the car was designed with. Im not saying that such variations wont work but that you should be cautious with them.
STAGE 5
With the spring rates pegged, you now have a platform upon which you can perform changes to another candidate for the Most Important Component Setting award the Dampers!
Getting the damper values dialled in to match the spring rates can do wonders for the handling of a given car. As with so much of tuning within GT3, it can be something of a Black Art and is heavily dependant on driving style but, over time (and excessive reading on the subject of damped spring systems!), Ive come to the discovery that its actually quite simple to determine what the damper values should be initially set to.
I have to admit that this conclusion is based on the assumption that, within the game, the springs and the dampers are rated to match each other at maximum values. As GT3 doesnt give dampers any units of measurement, I had to take a fixed point of reference and that seemed a logical one. I added what Id researched about such things in the real world to that assumption, did a little maths, a graph or two and, voila:
The Rebound value is equal to half the spring rate for the end of the car the damper is at and the Bound between a quarter and a half of the Rebound.
However, its by no means assured that the outcome of my assumption is correct, all I can say is it seems to work (at least for the highly tuned cars most of us like to put together!).
Now this isnt set in stone, its just your starting point. From these first settings you can then begin to fine tune the dampers for your driving style, desired handling characteristics and specific courses.
As has been linked elsewhere in the Numbers, a good source of advice on this is Neil Roberts Article on Shock Tuning at
http://www.smithees-racetech.com.au/theory/shocktune1.html". Its straightforward reading and he breaks a cornering manoeuvre down into five phases rather than the more usual three (which can help in diagnosing where a particular problem lies).
STAGE 4 and STAGE 5 are actually somewhat of a combined process. Because the spring rate chosen was arrived at with a given bound/rebound setting (albeit the stock value for a fully custom suspension), you may find that, once you start to dial the dampers in, the springs appear to be too hard or too soft. In this case, you might have to begin altering the springs and the dampers together i.e. select a new spring rate, adjust the dampers to it as noted above and re-test. This violates the tuning maxim of Only change one thing at a time but springs and dampers are so closely integrated that sometimes you have no choice.
Once all this is done, you can move on to adjusting the LSD and the camber/toe/anti-roll bar equation. But thats a story for another day (is that a sigh of relief I hear!).