See first two pages of review article above. Bioavailable (“free” + “weakly bound”) T assay is a very standard result that attempts to measure non-SHBG bound testosterone by precipitating SHBG bound fraction using ammonium sulfate method.
https://www.labcorp.com/tests/143255/testosterone-free-and-weakly-bound
Testosterone that’s left is the human serum albumin bound test plus free test. It’s a long story how all these tests and terms came to be and if you want the gory details read the review above. Bottom line is that free T isn’t the end all be all as I mentioned in above post. We don’t truly know the interplay of free T, SHBG bound T, and HSA bound T in the body and the specific roles of each.
HSA bound [ “weakly bound” ] T is the bastard stepchild T that never gets any love on the forums or by many providers.
Look here if you want “simple” math on how to estimate each bucket:
If you plug in your numbers here you can test theory vs your individual experimental data from labcorp:
http://www.issam.ch/freetesto.htm
In your particular “hit the gas” example the majority of the T is protein/HSA bound T, not SHBG bound, not free. No love for the poor HSA bound T!!