When I was about 13 we had a club after school to teach us road safety when riding our bikes. I had liked the sensation the saddle gave me a few times but didn't think much more about it.
One day we had the lesson during lunch break and the guy who was teaching us was quite good looking and we all fancied him. During the lesson we all lined out to face him and he was sat astride his bike talking to us about what we were going to do but I couldn't help looking at his tight shorts and I swear he had an erection as I could see it straining against his shorts. As he talked away my eyes were glued to his shorts and his hard penis, I began to feel a tingle between my own thighs and an itch in my pussy which made me want to squirm on my hard saddle.
Standing astride my bike I positioned the front pointy bit of my seat right between my legs and began to slowly rock against it enjoying my damp panties rubbing me and occasionally pressing down feeling the crotch slide in betweem my wet lips. As I looked around I think I wasn't the only one getting excited as my friend was doing the same and bright red in the face.
Later when we had finished I went to the loo and touched myself, my knickers were all wet and really pushed up into me so I rubbed myself some more through them until I came dreaming of the guy's hard penis in his shorts. Even now I still go for a ride to get off if I am horny thinking about our teacher. I usually wear a short miniskirt so it's just my panties between me and the pointy saddle enjoying the sensation as the cotton between my lips gets wet and rubs me off. Once I get home I usually go to my room and strip off except for my underwear and I spend ages tickling myself to orgasm through my gooey knickers.