When benching 80% RM is not relative to 80% RM for the squat since body weight is also involved in the squat. Therefore should the squat and similar exercises be adjusted relative to the total weight involved ie. 80% of bar plus body weight?
Why would you say that? Is there any reasoning behind it, or are you just throwing out an answer?
To Rich Hand, I take bodyweight into account when I lift. For lifts like the squat, I assume ~80% of bodyweight is being lifted, whereas it’s closer to 40-55% for DLs or good mornings. Lunges are ~80% as well.
As you have discovered, not taking bodyweight into account will lead to problems, especially at lower strength levels.
I don’t think its necessary to take into account bodyweight on the major lifts, including squats. The vast majority of lifters, including those the advocate RM type planning, don’t. There are a few exeptions, however. Weighted dips and pullup are two. The added weight probably represents less than half, and sometimes only a fraction, of the total load. If you hang 50lbs. around your waist for a 1RM dip, and you want to work at 85%RM, doing dips with 42.5#s on your belt won’t be correct. If you weight 150, your 1RM is 200 (body weight plus extra weight. So 85% is really 170, which is bodyweight plus 20.
Again, I don’t know anyone personally who uses this calculation for any lifts other than dips and pullups.
With using the bar weight only reduce you squat and bench press to 50% or 60% as when performing fast sets of 3 which powerlifters often in between their heavy sessions. You will probably find that bench feels much easier.
When I do fast sessions such as this I now use ~60% for the bench and ~40% bar weight for the squat which equates to ~65% when taking total body weight into account or ~60% if calculating the body weight at 80% as rj24 mentioned and which I think could be about right.
Similarly if altering the bar weight to 80% RM for each above exercise I get out a few more reps with the bench.