First “mountain-ish bike” was a Schwinn Stingray. I converted it over to full BMX from Sears catalog ordered parts! It was a BMX bike, not really MTB.
My next bike was a Raleigh C30 hybrid, rigid with twist grip shifter. I changed out the tires to full knobby for better off-road trail capability. Also replaced the cushie spring seat with a much better seat, and also swapped out the crazy long stem. Rode that mostly on fire access roads and multi-use trails in New England. I also rode some crazy trails with it that I should of not been able to with that bike. Great learning experience.
My first real dedicated MTB bike was a Airborne Zeppelin Elite. I upgraded the tires, rear shock, front shock, seat, seatpost, seat clamp, handlebars, grips, and stem. I still have it, and still use it sometimes.
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