1/18 Xray's will most definitely be too fast and too large for a track that sounds like it is smaller than a 1-car parking spot (is that correct)?
I actually have an indoor garage carpet track. Its in a single car parking spot and it works perfectly for 1/24th scale. I have mine set-up to switch between off-road and on-road courses (both carpet), one has jumps the other does not. I run Carisma 1/24th GT24B's for the offroad and a 1/24th Atomic AMZ 4WD shaft driven on-road car (for the on-road course).
W/ My Atomic 1/24th, I have the top speed turned down to about 40% and its perfect.
I have photos posted in other threads in the "mini/micro" section here. Check them out.