In my replays, I have a really hard time spinning and gaining momentum.
Every time I do a spin its always either slow or in a very akward position.
Can someone help?

I am not a pro as you would require but try to have a knee in front of you and spin the chest in the direction you want to. contract the pec which will be infront of spinning and also contract the other only for 5 frames and voila

its practice.
get a feel for how the game works with such stuff.

look at IRL video of spins and such, look how they "engage" a spin and try to look how u can import some of those muscle movements into the game to get momentum.

its hard to help with such a specific topic, this game is all about practice, gaining expierence, trial and error.

It helps to have your legs rather spread apart. Rotate your chest and pecs in one direction while extending the opposite hip. Use the ground if you have to. I find it really helps to get momentum buy kicking off the ground at many points throughout the replay as you're making a movement so that the movement is more powerful.

Here's a replay. It may not be the best example but it's the only good one I have lol

410: I go into a widespread position with my legs. In this replay, I overdid it and it looks a little ugly. I'm spinning right with my chest and pecs, and I'm extending my left hip. Contracting the glutes as you start spinning often makes you go faster, but you'll probably have to play with it for a bit.

385: You see my right leg? It's contracting at the hip, and extending at the knee. It gives me more spin and more speed.

372: Here's the "extra" kick I was talking about. My left leg is kicking once again off the ground. I'm getting more speed, and it makes me spin even faster. I also find it makes replays very appealing.

180: Again, I have the same widespread pose as I did before. I extend with my right hip and rotate to the left with my pecs and chest. All the while, I'm increasing the rotation by extending my left knee and contracting my left hip as I push off the floor.

I hope this helps just a little. It's hard to explain sometimes. If you watch some tricking replays, you'll see how often this method is utilised. Maybe not as much the kicking part, but the horse stance (spreaded glutes) is used in nearly all tricking replays.

look at IRL video of spins and such, look how they "engage" a spin and try to look how u can import some of those muscle movements into the game to get momentum.