For this story you may have to suspend disbelief and just go with the flow.
----------------------------------
We got on the motorcycle and headed towards the lake. The road was empty and the land around us was lush and green. I suddenly realized I was getting hard sitting behind her, smelling her hair, gripping her waist with my hands. Her ass was round and juicy in a short skirt and her perky tits were bouncing up and down in a plunging halter top with no bra. My pants were getting really tight over my crotch and the jolting of the bike was starting to play havoc with my senses. My erection was growing even more from the pulsations of the bike and from leaning forward with her ass nestled between my legs. I was enjoying it immensely but the blood rushing to my cock was making it hard to concentrate on anything but the pleasure.
I suddenly couldn't restrain myself anymore and felt a fierce need to give in to my urges. I slipped a hand under her shirt and heard her gasp as I pinched her nipple. I slipped my other hand under her shirt and started rolling both nipples in my fingers. I could feel her nipples getting hard and slowly trailed a hand down her stomach and under her waistband. I was painfully hard by now and knew she could feel it. I rubbed my fingers down her panties for a few moments and heard her breathing accelerate. I slipped her panties aside and started massaging her pussy lips with two fingers. She moaned softly but kept a firm grip on the bike. I could feel her getting wet and started rolling her clit around with one hand still doing the same to her left nipple. I abruptly pushed a finger into her pussy and started twirling it around in circles. She murmured, "oh god!" and started moaning even louder. I took my hand out from under her waistband and pulled up her skirt. My hand was already dripping from her juices.
I quickly unzipped my pants, pulled down my shorts and freed my cock. It felt glorious in the cool wind and even better when I pressed it up against her ass. I pushed aside her panties again and lifted her up with one arm. I gently let her down with her tight cunt slowly enveloping my penis until she was all the way down. Her black lacy thong was restraining my movements so I ripped it off and threw it into the wind. We hit a bump and she came down hard on my cock. We both gasped. "Oh god!" she screamed before she even had time to catch her breath. I started sliding her up and down on my cock. Every jolt of the bike, every vibration, felt incredible as she grinded down against my shaft and balls. She was riding me hard. Then she slowed down and started moving her hips in circles around my dick. Her pussy was flowing freely with juices by now and my cock was thick and hard inside her. She leaned forward and exclaimed loudly when I hit her g-spot. I was now rubbing her clit, rolling her nipple around, and nibbling the back of her neck. She was over stimulated and I knew she was going to cum hard any second now. She started screaming, "Fuck me, fuck me! God yeah, I'm going cum! Fuck my tight cunt with your hard cock! Yeah, make me scream, just like that! Yeah, yeah, yeah, yeah!" she cried until she let loose a roar and her pussy lips started quivering and squeezing my cock hard. We came together, our cum mingling together and running down her legs. "Shit!" She kept crying out.