I've got some fun data from my Draft bump marathon on Bluemoon bay today.
It seems SR gains and losses depend on your SR level as I was pretty consistently bumping for the entire race, a very good strategy. (Except in the first race where I ran out of fuel, oops)
Sat Feb 17 2018 14:54:37 GMT-0500 (Eastern Standard Time) -> DR:37761 | SR:99/99 | Races:1220 | DPUR:39
Sat Feb 17 2018 15:25:16 GMT-0500 (Eastern Standard Time) -> DR:50000 | SR:21/99 | Races:1221 | DPUR:200 12th -> 15th -88 SR
Sat Feb 17 2018 15:57:06 GMT-0500 (Eastern Standard Time) -> DR:50046 | SR:21/99 | Races:1222 | DPUR:200 3rd -> 1st -0 SR
Sat Feb 17 2018 16:53:17 GMT-0500 (Eastern Standard Time) -> DR:50127 | SR:30/99 | Races:1223 | DPUR:201 2nd -> 1st +9 Brand's hatch
Sat Feb 17 2018 17:25:37 GMT-0500 (Eastern Standard Time) -> DR:7000 | SR:1/99 | Races:1224 | DPUR:175 1st -> 1st -29 SR
Sat Feb 17 2018 17:57:40 GMT-0500 (Eastern Standard Time) -> DR:9744 | SR:54/99 | Races:1225 | DPUR:96 1st -> 1st +53 SR
Sat Feb 17 2018 18:56:47 GMT-0500 (Eastern Standard Time) -> DR:12676 | SR:45/99 | Races:1226 | DPUR:13 2nd -> 1st -9 SR
Sat Feb 17 2018 19:26:20 GMT-0500 (Eastern Standard Time) -> DR:13994 | SR:46/99 | Races:1227 | DPUR:20 1st -> 1st +1 SR
Sat Feb 17 2018 19:55:30 GMT-0500 (Eastern Standard Time) -> DR:15175 | SR:29/99 | Races:1228 | DPUR:26 3rd -> 2nd -17 SR
Sat Feb 17 2018 20:28:49 GMT-0500 (Eastern Standard Time) -> DR:16207 | SR:37/99 | Races:1229 | DPUR:31 1st -> 1st +8 SR
Sat Feb 17 2018 20:55:23 GMT-0500 (Eastern Standard Time) -> DR:17220 | SR:25/99 | Races:1230 | DPUR:36 1st -> 2nd -12 SR
Sat Feb 17 2018 21:30:36 GMT-0500 (Eastern Standard Time) -> DR:18280 | SR:42/99 | Races:1231 | DPUR:41 1st -> 1st +7 SR
Sat Feb 17 2018 22:15:31 GMT-0500 (Eastern Standard Time) -> DR:19464 | SR:38/99 | Races:1232 | DPUR:47 1st -> 1st -4 SR
Strategy for the race, start at fuel map 1 for the first two turns then switch to 2 while draft bumping, ideally trying to separate from the pack with one other car yet usually it took 5 laps or more to split off with 2 others. Pit at end of lap 13, continue draft bumping at fuel map 2, then switch to 1 for the last 4 or 5 laps while waiting for the right opportunity to slingshot and catch on to a back marker to secure the win. That is if the cars in front don't run out of fuel which also happened a few times.
One Brand's hatch race in between waiting for the 17:00 race. Maximum SR drop 88 points from SR.S, maximum gain 53 points from SR.E. I got the reset glitch first, setting my DR to 50k after the first drop to SR.C, the drop to SR.E reduced it to 7K.
My ratings are all screwed up now yet it turned out to be a very exciting set of races, pure strategy and a lot of carefully timed bumps, working together to get ahead. The best chase was when I got separated from 1st and 2nd place in an accidental wall hit and found a willing back marker to use to catch back up. Finished 2nd, close finish. No matter what SR I was, the racing was excellent with very little issues going through corners together. As the day went on more people caught on to draft bumping, more fun. Upside down world where the top 3 drop a whole SR level while the rest of the room has blue ratings.
The SR formula seems to oscillate and settle around 40 for the way I was driving.