I won all the races that the game has to offer, first place in all, but I can't win Abyss (it's the second one of the fouth [final] tier)!

The thing is, in the beggining of this track there is a tunnel that you MUST be on the second floor to have a chance of winning, if you fall down you can already restart the race... but it's so hard to stay on the top floor for two reasons: 1) in the beggining there is this tight curve and it's so hard make without falling, I tried many technics and combination, but I can go through it every time (I fall 70% of my tries), 2) the pod simply randomly explodes! Yes, it's a glitch, I make the turn and everything is ok and... BOOM! The pod explodes for no reason. And the worst thing is, I'm spawned on the bottom floor T-T

Anyone have some tip about this?! I already quitted trying...

So, nevermind, I just beat Abyss... I used an unlockable racer that I just read about here in the forum, is the one you have to press left ctrl+c+y (Cy Yunga) in the selection screen. I was there just to check if this racer was good and tested it in the Abyss race and.. .wow, the turn was a lot easier!! It took me 7-8 tries, but I beat it!! I was using Bullseye Navior... he's very bad for this race because he randomly explodes a lot, but Cy Yunga NEVER exploded and he turns really well.

I believe you are reading more into it than there is to it.
All that activating the secret characters will do, is to replace the 3D models and displayed name.
To my knowledge, the handling is kept from the racer they replace (also note that there is no slot for Jinn Reeso or Cy Yunga in the handling data).

At least I was unable to find code which patches the handling information when loading the cheat (I do however see the model and name patching).

I even had someone make screenshots of the stats screen before/after patching on N64.
On both, PC and N64, the stats did not change (as displated in the menu).
One could use the debug menu to verify this, but I'm too lazy to do it.

maybe it's the size and format of the pod. It's a fact for me, Bullseye Navior could do that turn really well (as Cy can, since he has the same stats) BUT Bullseye has a really high chance to randomly explode (in the middle of the curve and many times in the middle of the straight track after de curve). I never randomly exploded with Cy.... maybe it's due to the shape and size of his pod.

Interesting. I did notice that the spots where the pod and engines connect do change. So maybe that does have an effect on it. I'll look into it!

Do you know what the original "intended" framerate was? I'm assuming 25 or 30 or something in that neighborhood.

I've got the game setup through dgVoodo and I was originally able to run the game at 144hz but was noticing a lot of weird physics quirks, so I bumped it down to 60hz. It's better but not perfect. Thing is, I don't see an option for lowering it any further, 60 seems the be the lowest option that dgVoodoo allows for me.

Oh so slight necro but I believe the game was intended for 30 FPS? I could be wrong.

Anyway, try Nvidia Inspector. Lets you limit framerate to 29 or 30 FPS for individual games. Worked for me. It sucks because the game feels so nice in 60 FPS but it just doesn't function properly with sliding, Vengeance and Abyss.