Can TDCO be used to Fit jeans? Absolutely YES!
The principles are the same, TDCO is an inclusive method and there are lots of examples of people using this approach to successfully fit jeans.
I am a big advocate of people making what they are motivated to make. I don’t wish to discourage anyone but if you are LEARNING this approach to fitting, please begin with regular pants/trousers.
Why?
Reason #1 Construction
Jeans construction is more involved, with flat fell seams and top stitching. When testing the fit, it is easier to adjust the back darts on trousers rather than having to redo the yoke on jeans.
Reason #2 More Moving Parts
There is an additional pattern piece, the back yoke. More moving parts makes for more complications in handling and keeping track. Also makes assessment more challenging for novices, particularly if the jeans are closer fitting. The closer the garment conforms to the body contours, the more pattern elements are needed for the fit which translates to a more involved fitting evaluation. I see traditional sewists including professionals, mess up this part completely. I am sympathetic because there is so much mythology in the topic of pants fitting, it is hard to let go of assumptions particularly about different body shapes. You do not need more body measurements to fit pants with less ease, you just need to understand the design blueprint. Trousers are a good place to start learning.
Reason #3 Fabric
A big component of pant design is fabric type as well as design intent and the flexibility needed to respond to various body positions. Pants are sophisticated garments, taking full advantage of the range of fabric properties including different fabric grains on the same fabric. The diagonal weave of twill fabrics like denim and the resulting behavior of the fabric in the garment need experience to handle. It is not uncommon for a novice to find a pant leg is weirdly twisted or to make a pant in denim with great fit only to have it droop out within a short wear.
Reason #4 Psychology
We often have complicated feelings about our bodies, and how pants and jeans should fit. It is quite overwhelming to be your own fit model and evaluate the fit, especially if the body is accustomed to the sensation of stretch fabrics for closely fitted garments. Of course, this may not be the case for everyone but the fitting process is tricky. Give yourself time and space to learn, I always suggest fitting in short 10 minute bursts and starting with a quality multi-sized pants pattern to learn the approach.
Conclusion
Top Down, Center Out involves respecting the design, using it as a blueprint to build the relationship between design, body and fabric.
From my observations and coaching of people who have tried Top Down, Center Out, learning require going through the entire process at least once by yourself. It is not a trivial skill and there are no shortcuts. The good news is that trouser fitting is within reach and very doable by yourself. Even if you only just acquired a sewing machine, making well-fitting pants can be a first project.
When you get more adept at this method it will be easier to see how it can be applied to self-drafted patterns, all types of waist treatments, correcting pattern drafting mistakes, hacking the design, adapting the style and so on.
Great points, all. One thing I keep coming back to is that the fit of jeans, unlike other types of trousers, can change significantly over time. The denim breaks in, seams elongate, wrinkles soften. So the toile is really just a halfway point on the way to the final fit. No matter what fitting method one uses, time is an additional variable to consider when fitting jeans.