I am aware of those statistics.
What was new to me was that the percentage of pre-trial detainees is higher than the total percentage of prisoners in many other countries.
So next time I meet or communicate with an American who thinks that "innocent until proven guilty" is a unique feature of the American legal system, I won't need to explain to them that this was a part of Roman law since long before Common Law existed. Instead I can just point out that Americans still have a higher chance of being behind bars without trial at any moment, no matter what they might think about other countries' judicial systems.
About the racial aspects of the American prison system - are there any reliable sources that have numbers for the different causes? Police racism, judicial racism, poverty, laws that punish some kinds of crime more harshly than others are probably all factors that contribute to the racial asymmetry, but from across the ocean, I can't even guess about which factors are dominant, which are minor and which are just theoretical in nature.
Interestingly, the will to disenfranchise people is one of those things that the Brexiters are very proud of. Britain has been blatantly violating the European Convention on Human Rights and ignoring court rulings for some time now. And that's just about allowing people to vote while they are in prison.