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I've seen these for several Traxxas vehicles, but what is so "cheater" about it?

http://www.ebay.com/itm/Vintage-THORP-5307-Traxxas-Blue-Eagle-Nitro-Hawk-SRT-LS-Delrin-Cheater-Top-Gear-/200972426209?pt=Radio_Control_Parts_Accessories&hash=item2ecae3dbe1

More durable and lighter weight so less rotating mass i suspect.don