Well let me break it down for you. The poll for this thread indicates 44% of people go tts, 23% of people find tts snug, while 28% of people 0.5up. So first off that's an indication to me that if maybe I have a wide foot I should go up have a size. Having said that I do not like my sneakers snug. Secondly, I've asked some people that own fk racers and they've also indicated tts if normal width foot and 0.5up if wider than normal. I would say generally for most shoes I'm good with TTS but sometimes have width issues and these shoes look particularly skinny/narrow. Last, I don't own any racers so I don't know my size so worst case scenario I return (probably a pain in the *** overseas) or resell.
Long story short I don't own any racers so this is a somewhat of a guessing game for me.
Thankfully there's places like NT where one can get a sense of sizing before ordering something online.