Can anyone give me small description on how to do this.. and does it also work on DS2 ?
Something from a quick google search:
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There is a great way to adjust certain settings on your car during a race, very useful for the longer endurance races, especially those that have variable weather conditions.
With this, you can adjust brake bias, ABS, TCS, etc.
Here's how to set it up for the DS3 (aka- the normal joyapd controller), you can also set up some wheels to access this too, depending on GT5's support for your own wheel.
Go to the button assignment menu, and select which button you want to bring the in-race menu up with. I would choose L3 (which is downclick on the left stick), but you can use whatever comes easy to hand while you are actually driving, so that it doesn't make you lose control.
Then select the traditional direction buttons to select setting and to adjust the chosen setting. I would choose the UP and DOWN to scroll through to select the setting to adjust, and LEFT and RIGHT to adjust the values of the chosen setting.
So now, during the race, pressing L3 will bring up the menu which looks like the picture below. Use UP/DOWN to select the setting to change, and LEFT/RIGHT to decrease/increase the value of that setting. L3 will also close the menu or it will close by itself ofter a few seconds.
Edit: Source-
http://gt5cheats.com/forum/index.php?topic=2337.msg19535#msg19535