400EX rear sprocket size?

[TRXman86]

what is a good rear sprocket size for a 400ex with 18" rear tires for a good holeshot? getting ready to buy one and need to know. also, what is stock front size?

[nicktrx400ex]

15/38 stock gearing on a 400ex

if you want the speed and stuff to feel the same as when you had stock 20inch tires the go down 2-3 teeth on the rear or up one in front.