Posted by: Ride.DMC
... I was expecting my seat tub angle to steepen up a little bit with the angle set installed and was kind of surprised to see no change. I think it may be more of an issue with my phone not being the most accurate measuring device, or something like that - because it makes sense that it would get slightly steeper. Maybe not 2 degrees, but something.
I also put a -2° Works Angleset on my 2019 Process. Mine is an XL 29, so my numbers will be slightly different than yours. But I built a model in CAD to fully examine what was going to change as a result of the angle set (and bumping the fork up to 170), so I can help explain what's going on here.
The first thing to note is that an angle set doesn't change the "Head Tube Angle" as stated in a static geometry chart, it changes the angle that the fork goes through the headtube, which in turn drives a bunch of other changes.
We can look at this in three states.
State 1: Stock Geometry
Your static geometry is (approximately within tolerances) equal to what the manufacturer puts on their geo chart
State 2: You clamp your bike as it stands in State 1 and install a -2° Angle Set. Your geometry is now as follows
Head Tube Angle: -2° Relative to stock (64° in this case)
Wheel base: increases, but your front wheel no longer touches the ground ( Your fork length hasn't changed, but you've angled the fork outwards)
Everything else: no change (but again, your front wheel is floating in the air)
State 3: You unclamp your bike from State 2 and place both wheel on the ground (The bike rotates around the rear axle until the front wheel touches the ground)
State 3 Relative to State 2:
Head Angle: Steepens slightly
Seat Tube Angle: Steepens Slightly
Wheelbase: Decreases Slightly
BB Height: Lowers
Reach: Increases slightly
Stack: Lowers Slightly
State 3 Geo Static Chart (for XL Process 29 with -2° Works Angle Set, 160mm Fork, 51mm Offset)
Head Angle: 64.39° (from 66°)
Seat Angle: 76.16 (from 75.7°)
Wheel Base: 1276.69 (from 1258)
BB Height: 343.12 (from 346)
Reach: 511.87 (from 510)
Stack: 625.35 (from 630)
Alot of these angular changes are too small for your iPhone to measure well, especially when you have to deal with buttons making the sides not flat. (Also all these numbers are basically theoretical, the two decimal places are not particularly useful, and there will be tolerances etc. so they're not exactly representative of a given real bike)
This is where your "effective reach" measurement comes into play, your steerer tube is now more angled back towards you, so your handlebars have moved back because they're held in a stem, not located at a theoretical point, which is why your "effective reach" is reduced. And as you said, stem spacers now have an increased effect on your effective reach, because your fork is intersecting your frame at a greater angle.
What I think you should be looking at is your hand position relative to your BB, in the horizontal and vertical directions. You can then use a combination of handlebars, stems, and spacers to place your hands where you need them relative the BB, which may be in a different place than you had them before, as your front wheel is now farther away