Follow along with me on YouTube with Rivet's Swayback Adjustment Video HERE.
What exactly does swayback mean, anyway? It's not a dance move, although it should be. Swayback refers to the curvature of the spine. It can be caused by a forward tilt of the pelvis, a backward tilt of the torso, or both.
Why does this matter? It matters because it alters how fabric sits on your body. These tilts change your posture. The hip bones/belly will protrude slightly more (possibly increasing the front rise of pants or you may need a bit extra length at center front for tops/dresses). Your center back length is going to shorten by the amount of the tilt. In the graphic, the blue arrow is indicating the center back. When the pelvis tilts forward, the small of the back is curved more (pink arrow), resulting in the blue arrow (center back) becoming a smaller distance.
This is what we're going to focus on in this post. To be clear, this is a swayback adjustment ONLY for knits with no darts. When we create a garment, we are asking a 2D creation to fit our 3D bodies. When we use knit, we rely on the stretch of the fabric to accommodate those curves and valleys. Hence, you will always, always have wrinkles BECAUSE we are 3D, and also not static mannequins. The only way to really get a primo fit is with darts because darts create 3D curves in a garment. Most knit garments do not have darts, so here we are. The goal is not to eliminate wrinkles, but to minimize EXCESS wrinkles.
What are we looking for, exactly? In a knit top/dress, swayback presents itself as excess fabric in the lower back. This can also be caused for a few other reasons. If your waistline is too low, the fabric will move up to find the waistline. Make sure you have Adjusted your Pattern for Length first. Similarly, if the fabric is too tight at the hip, it will also want to move north to find a smaller part of you. Make sure you've Graded for YOUR Body properly. Even if you don't have a 'swayback', everyone's lower back curves inward and can benefit from learning how to better shape. Here is a very good example. See how the excess fabric pools at the lower back?
So... what can you do about it? We're going to go over a few options, depending on what type of garment you have. The first alteration we'll go over is the simplest and uses a center back seam. This is also the best one for those who do not have swayback, but still want some shaping in the lower back for a better fit. If your pattern back bodice is cut on the fold, it's super simple to add a back seam. Using a straight ruler, add a seam allowance to the center back fold line. I use 3/8" since that is my standard. You'll then cut two as mirror images instead of one on the fold.
BASIC CENTER BACK SHAPING:
This is the easiest one and suitable for those wanting a bit more shaping, and also minimal swayback. Sew the center back seam, shoulder seams, and side seams. Pop your bodice on inside out. Gently pinch out and pin some of the excess fabric in the lower back. You don't want it too tight or you'll cause wrinkles in other places. Baste the extra fabric out and try on the bodice right sides out. Keep doing this until you are pleased with the results.
PATTERN ALTERATION WITH CENTER BACK SEAM
1. This one is a more in-depth and accurate way of removing the excess fabric in a bodice with a center back seam. First thing you'll need to do is to try your muslin on and determine where and how much fabric you need to remove. Pin the excess out of the center back, against your spine. Take your muslin off, mark where the pins are, and then transfer those marks to the center back of your pattern piece. Depending on your body and your pattern, this may be above, below, or at the waistline. It doesn't matter, as long is it where YOU need it to be.
2. Find the center point between your two marks and draw a line to, but not through, the side seam. Then draw two more lines from each of the marks to meet the first line at the side seam. Look a bit like a dart now, right?
3. Cut the UPPER line from center back to, but not through, the side seam, creating a hinge.
4. Bring the top of the bodice down at the center back to match the bottom mark and tape into place.
5. There. Now you have reduced the center back while still maintaining the side seams. One last thing... what about grainline? You'll need to straighten it. You can either leave the upper bodice tilted, or the lower. For a top/tunic, I'd leave the lower bodice tilted and straighten the top (left image). For a dress, I'd probably leave the top portion tilted and straighten the bottom to maintain the hemline on the original grain (right).
PATTERN ALTERATION FOR NO BACK SEAM
If you really, really do not want a center back seam, it is possible to do a swayback adjustment without adding one. It's not my favorite because it's not as accurate and does some funky things with the grainline. BUT. It will work. Follow steps 1-4 above using your original cut on the fold back bodice piece. Before we straighten the grainline, we need to do a couple more things. First, redraw a straight FOLD line at center back. Do you see how when you do that, you add width to the bodice? You then need to take out the same amount, at the same places, at the side seam.
NOW you can straighten out the grainline.
PATTERN ALTERATION FOR HORIZONTAL WAIST SEAM
This type of a swayback alteration is much easier since the seam is already there for you, right where you need it. Most of the time, this is for a bodice that is being attached to a skirt, but can also apply to a cropped top. Scoop out the bottom of the center back bodice, gently drawing to nothing at the side seam. For attaching a skirt (or any bottoms), you will want to evenly distribute the amount you remove so that the horizontal seam sits evenly.
Fantastic! I hope you will find this helpful in your tops and dress sewing!
