I've worked a lot on Stk today and i'm happy to show you what i've made

1) The current particle for skidding is smoke


-the 2 Skid particle (in texture folder)
-two xml files (in gfx folder)
2) Current "zipper" particle is rather the same as nitro particle so i changed that, and it has coherence with the new icon i was working. You have to change 2 files for that
-The icon (in model folder)
-Zipper particle (in texture folder)
You can download the .zip file
Here few pictures to illustrate (the second is "zipper" particle and the third is skidding particle "level 2")




I wish you a merry christmas in advance

