From what I understand about TCP BBR from reading about it the past few minutes, it would compute a new link speed as a result of impacts from WRED and then use that for the connection baseline speed.

TCP BBR would still rely on RED/WRED to compute the connection rate estimate initially, then it would attempt to send below that rate to avoid packet loss. If packet loss is detected it would recompute the estimated connection rate.

I found this page [0] useful, especially the graphs.

[0] https://blog.apnic.net/2017/05/09/bbr-new-kid-tcp-block/