Daddy Pig Bikes: Gravel build - Put the brakes on

Original though for this was to re-use existing post-mount brakes on this build.

Even though the frame and fork have flat mounts, for now the plan was to use components I already had, as there are adapters available for this.

That would mean less pleasant aesthetics but cheaper cost (also the pads are usually much cheaper for postmount stuff).

So, aesthetics wise, with the adapters the solution is simply FUGLY.

As an example pic stolen from here, we can see from left to right:
Postmount caliper on postmount.
Flatmount caliper on flatmount.

Postmount caliper on flatmount fork (see, fugly).

So, doing this on the fork was ok as basically there is nothing behind the fork.
Tried the frame and ... no way in hell it is going to fit.
Even just the adapter alone does not fit (hits the seatstay), so no way in hell.
I need to get new flatmount brakes.

(I could just get one for the rear and use the adapter in front ... but ... fugly ! )

Choice was to the trusted (and currently on sale) TRP Spyre SLC (carbon wooooo).

There are not much options on mechanical flatmount disc brakes, and these work "OK".
Dual-sided (both pads move, unlike most mechanical disc brakes), use easy to find pads.

What I mean by "OK" is that it is not as good as good hydraulics, but is more than enough for the purpose when paired with compression-less cable housing, good rotors and pads.

Why mechanical ?
Simply because they are much cheaper. I can re-use existing STI levers.
If I drop the bike and break a lever or want to upgrade transmission, much cheaper to buy mechanical.
It is simpler to maintain if I am backpacking somewhere remote, It is simpler to hack something out to fix a cable, rather than look for a hose / bleed kit / hydraulic fluid in the middle of Morocco with a goat on my back.

Getting back to the build.

Got the brakes, installed them in 160mm configuration and done !!

Oh, just one thing, replace the TRP pads ;) You'll thank me later.
(I will save them for the road bike, as I also use Spyres there and road is not so demanding on brakes).

SwissStop are a premium option, Shimano BS01 will also work fine for a budget pad.
(I heard wonders on TruckerCO pads (yes, strange name) but not been able to source them.)

One other thing, the length of the bolt for the rear brake depends on the frame stay width.
Learned it the hard way.

Measure it

29mm in this case, add 6 to 10mm ( so, 35 to 39mm will do ), look for bolts.

Available lengths are 27mm, 32mm, 37mm and 42mm.

Doing the math, in this case 32 is short(less than 35), 42 is long (more than 39), 37mm is just right !! Goldilocks.

ONE IMPORTANT NOTE :
If you order Shimano bolts, the size they mention is chainstay width. You order the 30mm version, to fit a 30mm chainstay, so you get a 37mm long bolt.

If you order TRP or SRAM bolts, you get what you order. 32mm gives you a 32mm long bolt.
(I also learned that the hard way).