We continue seeing players confused about what SL1R is, often mistaking it for some kind of spin-off remake of SLRR.

Here's some history :)

Pre-Street Legal:
Sidescrolling 2D action adventure featuring combat, platforming & puzzle elements.
Published by Sadeness Software.
Advanced 3D off-road racing featuring full real-time "soft body" chassis flex & damage.
Published by Codemasters.

Street Legal series:
Open world street racing featuring highly advanced powertrain & vehicle dynamics simulation, alongside in-depth customization & damage/maintenance elements.
Point-point racing, 16 cars, 4 engine types.
Published by Activision Value.
Also known as "Street Legal 2" / "Street Legal: Redline".
Since this release, the previous game is referred to by fans as "Street Legal 1".
Open world street racing built upon simulation & customization foundations set by SL1, now featuring fine-tuneable parts, day/night cycle & drag racing, increased detail & more.
Drag racing "night races", point-point "day races", R.O.C, 9 cars, 3 engine types.
Published by Activision Value.

Various technical & visual improvements, various redesigned visuals.
Added: Vehicle trade-in, 4 new engine types, port of Furrano from SL1, Sell All function.
10 cars, 7 engine types.
Developed by RAXAT, to-be founder of ImageCode.
Further improvements in most areas, rebalanced career, further redesigned visuals.
Added: Track racing events, paint booth, ports of the 15 other cars from SL1, custom map & Steam Workshop support.
25 cars, 7 engine types.
Directed by RAXAT, published by ImageCode.
Marketed as "Street Legal 1: REVision" for brevity.
SL1, ported to the engine of SLRR v2.3.1 for major technical improvements & mod sharing, retaining retro visuals.
Added: Career mutators & Junkman mode, completed Auto Shops feature, garage first person mode, night, cheats, Steam Workshop support.
16 cars, 4 engine types.
Directed by EvilMcSheep, published by ImageCode.

SL1 is a very different beast compared to Redline!

• Where Redline expects you to spend a significant amount of time tinkering with the car in the garage, SL1's simpler customization mechanics mean you'll be upgraded & ready to race in less than a minute!
  
• No 'Repair All' - any damage you do means individually disassembling the exact affected parts; Learning to quickly disassemble & reassemble each car & engine type are important skills.
  
• More simulation focus on damage, wear & their consequences.
  
• Endurance racing skill plays a major role.
  
• All progress happens during the equivalent of Redline day races - building a drag racer is not critical for progress.
  
• Good navigation skill is critical - staring at the navigator during the race is a great way to wreck.
  
• Strongly defined progression - you can only access 1/4 of what the game has to offer at the first club.
  
• Of course, almost all the included content (maps, cars, parts, sounds, music, menus...) is different from what you get with Redline, the only major exception being the (heavily modified) conversions of SL1 cars featured in v2.3.1.

Though SL1 compares to Redline, it is in no way a replacement for it; SL1 is an alternative for those who prefer a different gameplay experience, and/or want to explore the history of the series.
Both games will continue to receive updates :)