The first main groove is made of {HEAD ~ a see through groove} extending in {TAIL ~ the tire circumferential direction} 
extending in
The first main groove is made of { HEAD ~ a see through groove } extending in { TAIL ~ the tire circumferential direction }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL