Hey all - quick question I’ve never figured out with the brake list.
Drum (2LS) and Drum (SLS) - …what’s the difference please and thanks? 
Cheers for the help! 
SLS = Single Leading Shoe
2LS = Twin Leading Shoe
Basically, all drum brake have a pair of shoes inside a drum (drum brakes, see?).
Let me get back to you with some research in a bit, because I was under the impression that a twin-leading design was actually the interior one, but in the game, it the better option.
Don’t let me forget.
en.wikipedia.org/wiki/Single-le … drum_brake
en.wikipedia.org/wiki/Twin-lead … drum_brake
engineeringinspiration.co.uk/drumbrakes.html
Usable only were you don’t need to worry about reverse movement a twin leading shoe design maximizes the friction of a drum brake in one directing of rotation and is far more efficient in terms of stopping power than a leading/trailing shoe traditional design, however due to that design it is far less effective then the leading/trailing design when the wheel turns the opposite direction. For a quick over view of each type check the wiki links, to see why direction of travel matters check out the engineeringinspiration link.
I was wrong, I was getting twin-leading shoes confused with twin-servo brakes, different tech all the way.
Basically, a 2LS brake will have more stopping power than a SLS, as long as the car is moving forward, but because of its design, increasing forward stopping power basically eliminates any rear stopping power, so that’s why it’s a front-brake only option, both in game and in real life - SLS brakes are always at the back so there’s at least SOME braking pressure when you’re reversing, also, rear brake is (almost always) where the parking brake is installed.
Questions? I can try to clarify further, but wiki and Google are smarter than I am.