Being able to convert a regular bra into a racerback has several advantages. The racerback style of bra pulls the shoulders back, keeps the breasts from bouncing as much and redistributes the weight of the breasts, giving you better posture and a cleaner look under racerback-style tops. Converting a bra to a racerback requires no sewing skills and can be done in minutes without any permanent damage to the bra. You can also make the change more permanent, if you like, with a simple bit of sewing.
Cut a piece of elastic 4 inches long.
Put on your bra.
Have a friend slide the elastic under your bra straps, right below your shoulder blades.
Using the elastic, pull the straps together and tie the elastic into a bow.
Try the bra on. With a piece of chalk, have a friend mark a line on your bra strap just below your shoulder blade. Do this on each side. Make sure that the marks are even. This is the key to giving you a customized racerback with the perfect fit.
Take the bra off.
Place the straps side by side and pin them right above the marks and 2 inches below the marks.
Sew the straps together with a zigzag stitch at the marks you made. Keep sewing until the straps are sewn together 1 ½ inches down.
Reverse your sewing machine and sew over the seam you just made to make the racerback extra strong.
Put on the racerback by sliding your head and arms through the joined area as if you were putting on a t-shirt.
Do not overlap the straps to sew them. This will create an uncomfortable ridge in your straps that may rub your skin.