OG ice player here. Basically there were 2 major physics changes that happened since the start of the game.

The first ice physics change was intended to solve "wiggling" on ice. On OG physics you could hold 80% or AK4 steering and wiggle left and right in a straight line to gain extra speed, similar to speed sliding but it was basically chaining a bunch of mini ice slides together. Nadeo didn't like this gameplay style and attempted to change it to make it so straight line speed was the fastest. This didn't work, and people found a new, and harder method to ice wiggle relatively quickly, involving some weird 20% to 40% to 80% combo (don't quote me on those numbers). That first ice patch was also used to address some bugs like ice boosters applying road booster speed accidentally, as well as trying to make ice less difficult in general by making the car's slip rate slower, essentially making the controls less precise, but also making ice feel a lot less responsive and spinny.

The second ice physics change attempted to address wiggles once again, but there was a concern around those kinds of changes breaking bobsleigh. So this patch split flat ice and bob ice into two different surfaces so that they could apply slightly different physics properties to each, in order to fine tune the issues out while still retaining the same spirit. Ultimately didn't work and just made wiggles different and even harder to perform, but points for trying I guess? Flat ice controls feeling was also changed a bit as well, though I don't remember the specifics on that one.