Yeah but for example do you start off with stock suspension or the fully customizationable one because the settings are different so the car will handle different
IMO you should start with
1: tires
2: brakes
3: suspension
4: LSD
Or not? By the way downforce also alters your grip so you have to test this before setting up your suspension correct me if i'm wrong..
I just want to know if there's any sort of routine to tuning the settings
I think the most important thing to begin with is to get yourself organised for the tuning process.
There is no way to tune with out having a few blank tuning record sheets that you can download off the GTPlanet site here. So you decide on a car to tune, picking a Front engine Rear drive is the easiest, and then look over the stock settings before you do ANYTHING! Fillout a tuning sheet with the stock settings. This sheet can be used as a reference so that you know how the car was setup by the factory. You will probably not use this stock setting sheet that much, but at the very least you have a starting point.
You have now educated yourself on your car of choice and you can bring the car back to stock settings if you want to, or, just partly back to stock. If you follow this procedure you might notice for instance that when you start adding modifications to the your car, these stock setting may change with the new parts. For instance let's say you purchase the fully customisable supension mod. The ride height may now be different than stock! This, without you changing anything yourself! So you can see that having that stock setting sheet is valuable because the original factory settings could be lost, or difficult to get back to.
Start a new setting sheet for the tuning of the car now, and set the stock car settings aside for reference.
One of the first things I look at is how much the car weighs. If it between 1200 kg and 1400 kg then it is OK to start tuning as is. If not, I use the weight reduction feature first to get it into the ball park. Less weight is always better. A light car will accelerate faster, stop faster, and go around corners faster. Tire wear will also be less on a lighter car than a heavier car. Keep in mind that weight reduction wil cause the PP to go higher, a worthwhile penalty if the car is heavy, like a Bimmer or Jaguar. If your intent is to soup this car to the max, then the weight reduction penalty in PP in addition to your other mods can add up to a very high PP at the end of your tuning, so much so that you can put the car into a PP that is in the realm of race cars. This could make it unuseable in some lower classes.
One of the nice features of GT-6, is that the mods are mostly reversible, so you could remove tuning modifications for instance if you paint yourself into a PP corner. I will sometimes soup up a car to the max, and then if I want to put it into a lower class race, I just remove the turbocharger or supercharger or the headers, etc until I get it down to the required PP.
I noticed that you were attracted to lowering the car to the max in an earlier post. Be aware that the car designer set the car up to be able to cope with TOPES (speedbumps) in Mexico with a smooth ride and lots of travel for potholes and other bumps. So if you lower a car from the stock settings, then you will have to compensate by adding stiffer springs. Otherwise the car will "bottom out" and then spin out as a result of having no travel left in the supension. So tracks like La Sarthe and Nurburgring (Nordschliefe) are quite bumpy, spending time as normal roads. For these tracks most tuners will have a special supension tune with softer springs, more travel and higher ride height to accomodate the bumps at 200 mph.
Some of the better tuners will actually raise the ride height of some of the higher performance cars, so don't think that "slamming " a car is a requirement for speed in all cars. That said, lowering the ride height usually helps, but it's a good thing to leave a little remaining, so that front to rear ride height tuning is still available, after generally lowering the car.
The tuning sheet can be followed generally from top to bottom if you are wondering where to start, and you will notice "Ride Height" is at the top of the page. Most important, is to do a lot of reading first. There is so much to learn, and one change affects another so, patience is required.
Finding your test track of choice is very important. I keep a notebook and log my times around different tracks in different cars. If you get really familiar with one simple track first like say, Tsukuba, then you will build an experience base to test on when you are tuning your first car. You could start with the totally stock car and work from that as you modify. You must do at least 3 laps after each tuning change, and preferably 5 laps which is only 5 or so minutes on Tsukuba. Work on consistency in your times with a known car so that all your times are within 2 or 3 seconds on a 5 lap session. You need this base consistency to know whether your tuning changes have made a difference, that's why it's good to run the car stock first, with the tires that you want to tune on, for maybe 20 or 25 laps, and record the average time. After a while you will find yourself lapping within 1 second on a short track like Tsukuba, and then you can reliably find gains or losses from your tuning modifications.
This is a personal opinion, but I will say that my consistency really improved with the purchase of a Logitec G-27 wheel and pedal set. Now, I would never go back the dinky little controller that came with the PS3, I found it like trying to fly an airplane with the tiller of a sailing dinghy. The control available with a wheel is like 100% better and my driving and lap times improved amazingly. The wheel also provides feel feedback. If I am driving a Porche, I can feel the heavy ass-end in the corners and especially braking in the corners! Every car has it's own feel with the wheel and to me that makes the game a simulator.
Happy Tuning!
Mustangxr