There's been an interesting discussion of grainlines on pants on the Sewing World SIPP Thread. It's got me thinking about grainlines, but I haven't got time right now to go dig out some pants patterns and compare them.
I've heard some instructors over the last few years that have said the grainline needs to be shifted on pants; but the way they describe shifting the grainline involve drawing a line parallel to the grainline somewhere other than where it was originally stamped on the pattern...usually moving the line to the center of the leg. Ok, sure, you've drawn a new line, but you haven't changed the grain of the pants. If the grainline drawn on the pattern is parallel to the center of the leg, the center was on grain before the 'new' line was drawn.
The specific discussion is how grainline relates to the seams; Loes Hinse's Oxford Pants are the main topic of discussion; it just so happens that the first pair of Oxfords I made I made from a plaid fabric,so the grainline is easy to see. (Click on the photo icon on the review, wait forever for Photoworks to bring up the whole album front page, click on 'launch slideshow' and then 'view pictures larger' to see it the best). You can see in the photo that both the side seam and the center front seam are on-grain...which means both those seams were cut parallel to the grainline. The grainline just determines how the pattern is placed on the fabric; the seams are products of pattern drafting and can be drawn parallel to the grain if the designer so chooses. In other words, the grainline shouldn't determine the seam line. But consensus is that, if the outseam is on grain (cut parallel to the grainline) the pants will hang very nicely.
At least, that's what I think...when I've got time, I'll pull some patterns out and do some comparision. Meantime, I'm still sewing costumes...gotta have 'em done tomorrow.