High tension flatwounds?

Too much is said about the numbers on flats. But that said, Chromes are pretty stiff. Rotosound are even stiffer. But I believe the consensus is that the heaviest flats, as a set, are the La Bella Jamersons.

Don't confuse tension with feel. And unless you want terminal thump, don't get too large a gauge because the strings will actually lose overtones and sustain. That is why the Jamerson set is at the limit, about 110, for what is still a playable E string.

 

There's also the Ernie Ball Group I flats — .110, .090, .075, .055. I have a set of these and a set of the LaBella Original '54s (Jamersons) on similar basses, and they feel similar in tension. But also take note that I down tune and play in D-standard.

Rotosound flats certainly feel higher tension for their size. I have been meaning to try out a set of the Steve Harris signature set (.110, .095, .075, .050), but have not done so yet.