How to Cut a Tri Tip: If you look at a raw tri tip you'll see that each end has the grains running in a different direction. Roughly half of it has grains that run vertically and while the other half run at a diagonal. These are easiest to see when the roast is raw, so make a mental note or take a picture so you remember which end is which. When it's time to cut the tri tip you want to cut across the grain, because this will give you those perfectly tender slices. So each half of the tri-tip will be cut at a different angle according to the direction of the grain. It may be easiest to cut your finished roast in half where those grains shift directions, and then slice each half against the grain. When slicing, angle your knife slightly; this is called cutting "on a bias". The thickness of the slices is purely personal preference. Slice your tri tip however thinly or thickly you prefer.