The reason why plastic wheels are spoked because on impact the spokes have room to flex and compress to take in to shock. thats also why cheap plain old plastic cracks right away, and why nylon (rubberish) takes the impact and doesnt crack. If a wheel was full core and plastic it would just crack and shatter since all the impact just goes straight through the core. no room to flex/cheap plastic = crack. nylon = rubberish = flex and no cracks. Capiche?