Tuning Theory and Tuning Tips
Nothing can substitute testing and tweaking a tune. Trial and error. Even after completing a tune, you could maybe think of some type of settings that you didn't try. So you could go back and test again the tune: low and stiff, high and soft, low and soft, high and stiff (just to confirm to yourself that the tune you made is going to be better than some random settings at least). Sometimes you may surprise yourself. If you start somewhere bad and head in the wrong direction with your tune you can end up with something truly terrible. But when you have got something you think is reasonable, make sure to write it down somewhere!
Ride height
I generally like higher ride heights and I generally like even ride heights. One thing that seems to help a tune with higher ride height is higher roll bars. I don't agree that a tune should be as low as possible, but high enough that it doesn't bottom out. Sometimes a higher ride height just works overall better.
Spring Rate
Most people seem to get spring rate without being told. For me, hard springs will reduce the body movement between front and rear during braking and acceleration as well as body movement to the side during cornering. For me, roll bars are additional to reduce body movement to the side during cornering. Consider combining a softer front spring with an increased front roll bar to achieve increased body movement to the front under braking but controlled body movement to the side during cornering.
Dampers
Dampers play a part in ride control while negotiating bumps, kerbs, jumps, etc.as well as effect body movement during braking, accelerating and cornering.
Sometimes I will set dampers purely to negotiate kerbs well. If your car can ride kerbs well, you have more space on the track you can work with, you can take sectors of track faster and gain a lap time advantage.
Dampers control the movement of a spring, especially instantaneous movement from bumps and the moment brakes or accelerator are first applied.
Low front bound will allow the front of a car to dip more when brakes are applied. Low front rebound will allow the front to raise more when accelerator is applied.
Low bound and high rebound (front and rear) can have interesting results when taking high speed corners like at the top of Bathurst mountain. Suspension on both inside wheels wants to extend but is heavily restricted and suspension on both outside wheels wants to compress and is not so restricted. These settings seem to work extremely well for these corners.
Very low rebound is the best setting to allow suspension to extend quickly, so after suspension is compressed after hitting a kerb, the tyres will maintain the best possible contact with the road.
It might also be useful to think of weight transferring diagonally across the car (like how a stool or table rocks). It's not going to be of any benefit while a car is braking or accelerating in a straight line, but while braking and turning, it may be of use.
Roll Bars
I consider roll bars are additional to springs for reducing body movement to the side during cornering.
Generally the theory goes: soft front roll bar and hard rear roll bar is reduced understeer and increased oversteer.
I have found that higher rear roll bars on cars with rear weight bias (MR cars) can reduce weight shifting sideways at the rear of the car and reduce oversteer under certain conditions.
You might also find increasing the front roll bar a little increases the integrity of the front suspension and increases grip on the front wheels which reduces understeer.
Now that camber physics are changed, you might find that soft roll bars matches nicely to higher negative camber and harder roll bars with lower negative camber.
Negative Camber
Camber physics are changed at update 1.09. Initial opinions on 1.09 suggest camber physics are improved. Proper camber adjustment should give optimum contact patch while cornering. Camber should be adjusted to give maximum lap time advantage.
You should aim to set it to maximise surface area between the tyres and road during cornering. Having negative camber will help the loaded (outside) tyres during cornering but it will have a negative effect on the unloaded (inside) tyres. The overall effect is a gain in cornering ability when it is set right.
Negative camber will reduce the tyres contact patch while driving in a straight line and will have a negative effect on braking.
It might seem like the ideal solution would be to reduce the amount that the car weight shifts to the outside wheels so you need less negative camber and your inside wheels are more effective during cornering and your brakes are more effective but, just like lowering your car as low as possible, it just doesn't work out like you want sometimes.
Toe
Toe settings is one area a tuner may get an advantage over many other tuners because toe is typically set to 0.0 / 0.0 by most tuners. You can add rear toe to make a car more stable, you can add negative rear toe to make a car less stable. You can add negative front toe to make steering more responsive maybe.
Brakes
I drive with ABS off a lot but I don't put too much emphasis on brake settings for a tune. If a car is rear heavy, I may have rear brake bias, otherwise my brakes are set even or with some front bias. I like to fit racing brakes on every tune, it seems better to me, although I don't have any hard evidence that they improve lap times. If a tune seems to have bad breaking performance I may try higher brake values, if a tune tends to lock brakes too easily I may try lower values.
Transmission
I will typically set max speed first. I will eye it in so top gear will achieve a slightly higher top speed than I need. Next I usually set my top two gears as short as they go, this will lower top speed to about where I want it. I set second gear as tall as it goes and the middle gears I will set to how I want them.
Typically I will make second to third and third to fourth very short shifts. This gives my tunes very nice acceleration between 100km/h and 200km/h.
After some testing, I will set the final ratio to where I like it and adjust the other ratios as I need.
Some cars that only have 5 speeds, I will use the transmission trick, like that mid engine, mazda rotary race car thing.
Transmission can be tuned specifically to a circuit, that is the ratios throughout the gearbox selected specifically to perform at the maximum for a circuit. Transmission may be tuned to prevent the need to make gear changes during cornering, to eliminate the need to change up gears right before a braking zone, to facilitate better short shifting during corner exit (I like to short shift into 4th for the exit onto the bridge on grand valley).
Transmission is best tuned last and can be tuned independently from other settings. Sometimes making wild changes to transmission can make very little difference to lap times and other times it can make significant difference.
If you become serious about a certain car and have a number of vastly different transmissions for different circuits, then it can be advantageous to try each transmission setup for each track. One track especially that a custom transmission is excellent for is Cote de Azure. Do not be surprised if this new transmission tuning is an improvement for other circuits also, 6th can be adjusted to match for other circuits.
A very tall change into top gear can be the best solution for a transmission. You may only need to change into top gear a small number of times during a lap and the poor acceleration in top gear while at lower rpm can be more than compensated for by better acceleration in 3rd, 4th and 5th.
LSD
Initial: Is either how fast the differential will engage or how much the differential is engaged while coasting.
Acceleration: How much the drive wheels turn together with acceleration. As far as I'm concerned, 60 is not completely locked. There are one or more cars with stock differentials with settings higher than 60, so how can 60 be completely locked?
Deceleration: How much the drive wheels turn together with deceleration.
By setting decent values with LSD you can give a real solid feel to your tunes which gives the driver real confidence. You can give the tune different characteristics in braking, coasting, accelerating. This is real advantageous to make slight adjustments to the cars handling with driver input. A little lift of throttle may allow the car to turn a little tighter preventing the driver from running wide on the exit of a bend.
A major problem with low accel settings is cars "floating" from apex to exit. With accel set close to completely loose, the unloaded drive wheel will spin. You basically have a one wheel drive car and it's always driving the wrong wheel.
A solution to this is obviously mid or high accel settings. You can come into problems with these settings 80% the way to the exit of the bend. Your car may go into a slow drift. To solve this you can go even higher with accel and/or a big increase of initial value. With high initial and high accel you might have your tune twitch a little after applying heavy throttle at the apex. For me this is acceptable, it takes some driver control but the car is generally stable and fast at the exit of the bend.
Power
I like to fit parts that allow for a flat torque curve to maximise PP. On the X-bow, I do not fit an aftermarket turbo. It would not give torque how I like. It's trial and error though, for a lot of other cars. I also like to use a decent amount of engine limiter. At the very minimum, I like to flatten off the top of a peaky horsepower curve. If a car reaches the desired PP with a very peaky horsepower curve, I will add a part(s) and use engine limiter.
Sometimes it is also advantageous to have even more power parts added and have even more engine limiter. You will have lower maximum horsepower (just slightly) but you will have your maximum power over a larger rpm range and more power and torque outside your sweet spot.
Body
You may gain an advantage from having a lighter car. You may gain an advantage by adjusting the position of ballast. You can add or cut little amounts of ballast to get the last few points of PP adjusted after getting almost the right amount with power parts and limiter.
Downforce: Front downforce increases front grip at speed. Rear downforce increases rear grip at speed. Downforce will reduce acceleration at speed and reduce top speed but lap times are generally faster with more downforce. Lap times may be slower on circuits with mostly high speed, full throttle sections.
Oil
Your tunes might benefit from having no oil change and just get the PP you want with power parts, limiter, weight reduction and ballast. Without an oil change, your horsepower will not vary over time. This is a huge advantage. If you want the absolute max from a car, or are not restricted by PP, or can't get the required PP without it, then sure, change the oil.
GT Auto
You can fit front aero, rear wing, flat floor etc for some cars. Flat floor will count towards PP, but might not be as effective as gaining PP from power parts, weight reduction, etc. Flat floor is typically a poor choice for a PP restricted tune.
Increased Rigidity
Will not count towards PP. Will change something with the car for handling. May or may not be advantageous. May be beneficial on some cars but not others.
I tested increased rigidity on an S2000, that was otherwise stock, at Bathurst and it was within half a second of my other S2000 that was completely stock. I drove both cars for 40 mins. I was thinking the car with increased rigidity was going to get the faster lap for most of the testing but in the end the stock car got the faster lap time. The difference was small and the fastest lap may well have been due to driver input, not settings.
If you increase rigidity right at the start of the tuning process, you will account for it as you develop your car in testing and as you refine your settings to perform to optimum.
If you develop a tune without it and install it last of all, it will likely have a negative effect on your tune. Assuming you actually had your tune performing well before installing it, there will be a change in the way the tune drives and there is a good chance you will spend a lot of time trying to neutralise the effect it made before getting the tune back to performing how it used to. There is also the possibility that you never get the tune to perform as well as it used to so make a note of the settings before adjusting them and be aware that in a worst case scenario, you may have to purchase a new car to return the tune to original condition.
The exact effect of increased rigidity is not certain but I like to think that it is equivalent to having your car lowered a little, your springs, shocks and roll bars increased a little. Or to put it another way, you can run higher ride height and have softer suspension with increased rigidity and have no overall loss of cornering ability but having superior ride over kerbs and bumps.
