A PA18 GND LOOPED ON AN INSTRUCTIONAL FLT. THE L WINGTIP CONTACTED THE GND WITH MINOR DAMAGE.

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DURING INSTRUCTION LEADING TO TAILWHEEL PIC ENDORSEMENT. TRANSITIONING STUDENT TO TKOFS AND LNDGS ON HARD SURFACED RWY; AFTER PRACTICING IN DIRT RWY. ACFT IS A PA18 (SUPER CUB) WITH TUNDRA TIRES. THESE TIRES; BEING MUCH LARGER; MAKE THE HANDLING MUCH TRICKIER ON LNDG; AS THEY BOUNCE MORE AND MAKE THE ACFT MORE DIFFICULT TO CTL ON TOUCHDOWN AND ROLLOUT. I WAS IN THE REAR SEAT; SO MY VIEW WAS RESTR. I HAD THE STUDENT PRACTICING 3 POINT LNDGS WITH 2 NOTCHES OF FLAPS. HE WAS MAKING GOOD PROGRESS; AND WE WERE ABOUT 1/2 WAY THROUGH THE TRAINING. ON THIS APCH; AS THE STUDENT WAS ATTEMPTING A 3 POINT LNDG; THE FINAL APCH LOOKED GOOD. AS HE FLARED AND TOUCHED DOWN; HE HAD JUST A BIT OF EXCESS AIRSPD AND BOUNCED BACK UP. AS WE BOUNCED UP; THE WIND SHIFTED TO THE L; AND WE STARTED DRIFTING L AND AIRSPD DROPPED OFF. I COULD NOT SEE ALL OF THIS. HE APPLIED L AILERON BUT NO RUDDER. THE TAIL STARTED TO COME AROUND; AND BEFORE I REALIZED WHAT HAD HAPPENED; WE WERE SUDDENLY VEERING OFF THE RWY INTO THE WEEDS. FULL RUDDER DID NOT HELP. THE BRAKES WERE NOT EFFECTIVE. WE DID A SLOW GND LOOP; GOING OFF THE RWY; AND THE L WINGTIP JUST GRAZED THE GND; TEARING THE FABRIC. A LCL MECH INSPECTED THE WING AND AIRFRAME; AND COULD FIND NO STRUCTURAL DAMAGE. FIRST SOME TORN FABRIC AND SLIGHTLY BENT RIBS. HE SAID IT WAS OK TO FLY. I FLEW IT BACK TO HURRICANE ARPT; ABOUT A 15 MIN FLT. IT HANDLED NORMALLY. WE HAD TAPED THE TORN FABRIC. FOR FUTURE REF; I WILL NOT RECOMMEND A TRANSITIONING STUDENT USE AN AIRPLANE WITH TUNDRA TIRES; SMALLER TIRES ARE EASIER TO HANDLE INITIALLY. AND I WILL HAVE TO BE MORE ON TOP OF THE SIT. CAN'T RELAX FOR A SECOND. I WILL ALSO EMPHASIZE MORE RUDDER PRACTICE DRILLS PRIOR TO PATTERN WORK.