well speaking of tweak,
all you want is that your car has equal amounts of grip left and right.
so, since grip is a nice formula; F = N* c where F is your grip, N is the tire load and c is the friction coefficient of the tire. when putting traction control on your tire actually you are making this c higher and thus giving more grip.
if the left tire has more grip than the right tire the car will be going sideways or turn when trothle is applied .
so that can come from many things, tweak, non-equal spring preloads and so on...
when your setting up your car do it in this order:
1 detweak your car using the method described a few posts above
2 balance your car using a balance tool like from xray. make sure your car has equal mass on left and right side, so if your running BL you'd have to add a little counter weight to the battery side
3 next, and this is kind of important, you should get equal loads on your tires.
disattach your four shocks from the suspension arms and leave hanging them on the shock tower
place a setup block under the front suspension. make sure its in line with the front tires. then you lift up the rear end with a 2mm imbus or anything with a sharp tip, make sure you lift it up in the center of the rear. now look at the distance between the tires and the setup board. if things aint equal you have to adjust your REAR downstop screws to get them equal. so if things are correct, your left and right tire come off the surface at the same time.
do this with the front suspension as well. this way you equalize the front suspension too.
4 now comes the tricky part
attach your front shocks and make sure the front suspension is settled by pushing down the front shock tower exactly in the middle a few times. now again get your 2mm imbus and lift the rear up again and again look if the tires come off equally. if not you'd have to adjust the FRONT shock collars. adjust them equally, so for instance if the rear left tire comes off earlier, you'd have to turn the left front shock collar counterclockwise and the front right shock clockwise. do this in small steps so you can get the front of the suspension precisely right.
in this way you use the rear suspension as a measuring device as it is totally straight because you've just straightend it with your downstops.
now attach your rear shocks and disattach your front shocks, turn your car around and do the same trick again
if you want your car to perform at its best you should do step 1, 3 and 4 before every run. this way you always have a balanced car.
tip, sometimes the uptravel of the suspension is not correctly achieved. sometimes the shocks are too short and act as a downstop instead of the downstopscrew. so if you're changing your cars downstop , check if the shocks are long enough for your new downstop setting. i had allot of trouble with this on my xray T2, untill i switched to TRF dampers, DUHHH
this setup tips for me were the difference between spot 9 in competition and top 3.