I'm trying to sew a pair of trousers for my son. The photos are from the first fitting. My son has gained a bit of weight from waist 36 to 36 5/8 and seat 41 3/8 to 42 1/2 inch.
I'm unsure whether simply letting out the side seams - for the tight waist - will provide sufficient room for the prominent seat, or if I need to adjust the seat angle or make additional alterations.
I'd be very grateful for any advice or suggestions.
I am very inexperienced, but looking at the photo from the rear I see similar strain-lines to those on a recent toil I made. I have successfully relieved it by letting out the fork on the underside/backside. This increases the length of the center-back seam, though I'll note that my seat is considerably flatter than your son's. You can see the effect I was dealing with here: https://www.handcrafttailor.com/forum/the-trousers-1/help-for-a-corpulent-bracetop-trouser?origin=member_posts_page I don't have photos of after making the alteration, but I will say it was significantly better. Though I also made alterations at the side seam. And I am a distinctly corpulent figure. The area above the prominence of the seat looks to be pulled fairly tight so perhaps your proposed adjustment at the side-seam would be a good adjustment to try first before messing with anything else. I notice that the trousers sit out significantly around the heel and are tight over calf, this is probably a matter of taste, but I wonder how much shaping you've done under the iron. My calves jet out prominently and I find I need to do a bit of shaping under the iron to get trousers to sit right on the lower leg.