There are many different categories of Ork Oddboys, but one of the more obscure classifications of such in recent editions are the Speed Freekz. See, whereas most Orks place "going fast" under "fighting" in their list of Da Most Fun Stuff Ta Do, Speed Freekz are the other way around. These Orks love to go fast - the faster, the better. They're addicted to riding machine, and their own hierarchy is based less on who's the biggest and strongest and more on who's got the snazziest, fastest, loudest rig to use. Really, Speed Freek warbosses and Big Mekz tend to be larger mostly because they're still Orky enough that "beat up everyone else and prove you deserve/can keep the best rig" is their natural instinct. As a side-effect, importance in a Speed Freek warband also plays into whether or not you own your own machine; Wartrukk and Warbuggie riders are better than common boyz, who have to share a single Trukk between them, but bikers are better than buggies, because they're lone-ork operations.
Other Orks regard Speed Freekz as arrogant, annoying, and generally touched in the head, but they're Orky enough to get tolerated, a lot like Flash Gitz and Stormboyz. And it can't be denied that Speed Freekz are useful; in a WAAAGH! it is the Speed Freekz who provide the reconnaissance, fast attack and aerial support of the orky forces. Particularly the last one; most Orks are rather leery of flying a plane, but Speed Freekz consider it the one thing that might be better than being a biker. Mekboyz are the only Orks who really like the Kult of Speed, and often have sympathies towards it, if not active membership.
Speed Freekz came into their own during the Third War for Armageddon global campaign in 2000, where they got their own "sub-army" list from the core Ork list. Aside from special rules reflecting their mechanized infantry status - all non-biker/trak/flying units have to start with a transport, they mobbed up by falling back towards the nearest free transport, all vehicles had to buy the Grot Riggers upgrade, and their Fast Response made them start drawing up reserves earlier - they got some unique upgrades, unique units, and a whole new array of units. The Kult of Speed army introduced the Biker Nobz, Warbike Outriders (Ork Warbikes with the Scouts special rule), Deth Koptas (the original form of Deffkoptas), and Guntrukkz, with a later White Dwarf issue finally adding the obvious Biker Warboss to the list. They could take Warbosses, Big Meks, and Biker Nobz as HQ; Stormboyz, 'Ard Boyz and Skarboyz as Elites; Warbikes, Warbuggies/Wartraks, Trukk Boyz and mounted squads of Tankbustas and Burna Boyz as Troops; Deth Koptas, Fighta-Bommerz and Warbike Outriders as Fast Attack, and Battlewagons, Looted Vehicles and Guntrukks as Heavy Support.
As editions moved past, the Speed Freekz stopped being overtly supported, much like the entire Ork Clanz structure (with attendant sub-army lists) of earlier editions. Still, their influence can still be felt in the modern ork army options and, to a lesser extent, the fluff, so if you like your orkz Mad Max style, then all it takes is a little tinkering before the mob'z a good 'un!
More recently, they've gotten a whole boxed game to themselves aptly named "Speed Freekz", which allows players to reenact some of their "races". Since the 8e Codex, it's also possible to set up a Speed Freekz themed list with the Evil Sunz Clan Kultur and the multiple vehicle options added with it.