The conventional deadlift is done using a standard 20 kg barbell in powerlifting. Trap bars have a hexagonal shape which you stand in (which is why they’re sometimes called “hex bars”) with sleeves on the end that let you load weight, and they have handles on either side that allow you to grip the bar with a neutral grip.
During my 8-week wave cycling program for the squat, I had also been using the trap bar to do some deadlifting once a week during the last half of the program. Prior to that, I was doing Romanian deadlifts at about 60% of my conventional deadlift 1 rep max to work on improving hamstring strength. After I tested my squat 1-rep max, I also decided to see whether I could lift more than my current 1 rep max of 210 kg. The video below shows me setting a new personal best at 220 kg, and I felt I still had a little more in the tank.
From my experience using the trap bar, I assume I can usually lift around 20-30 kg more on the trap bar than in the conventional deadlift using an Olympic bar. I was curious to see what the typical difference was and did some searching on the web. I came across Greg Nuckold’s very detailed review of the relative benefits of trap bar deadlift versus conventional deadlift (CDL) on his Strength by Science website. Originally sceptical of the value of the trap bar lift, Greg was convinced by the studies he reviewed that the trap bar lift was actually a better training option for people who are not wanting to compete in powerlifting, where the conventional deadlift is mandatory. He reviewed a number of studies and concluded that “the trap bar deadlift works your back and hip extensors almost as hard as the conventional deadlift does at worst, and just as hard in all likelihood, with the added benefit of also providing a little extra stimulus for your quads (though not nearly as much as squatting does).”
In particular, he examined two studies which assessed the difference in 1 rep max lifts for conventional and trapbar deadlift. For the study in which the lower trapbar grip was used (in line with the central axis of the weights), on average the study subjects could lift 8.4% more with the trap bar than the conventional deadlift.
The study that explicitly compared the high-handle trapbar lift with the conventional lift had a difference of 14.9 %. That would imply that my 220 kg high-handle trapbar lift would correspond to a conventional deadlift of 191.5 kg, very close to my previous personal best of 190 kg set pre-pandemic in 2019. I felt I was not quite at my absolute max when I lifted 220, so possibly my conventional deadlift has improved a little over the pandemic, though I have not been training it intensively. If I can get to a conventional deadlift of 200 kg soon, that would put me within 20 kg of the current drug-free European record for my age-weight class.