Joy Ride Turbo

I saw these videos posted in xbox360achievements.org
I think it could help in stunt parks. If I find something about the boxes in the tracks I will post here

Boxes in the tracks video guide

All credits goes to lillam111

Video order:

Aviator Ranch
Badlands Motorplex
Boathouse Bay
Cannon Crossover
Forbidden Fortress
Gold Rush Road
Great Dragon Road
Lighthouse Loop
Rocky Road Speedway
Twisted Canyon

If you give negative, say why

The videos in Joao Aden1lson & ro455BR's solutions are great & I already gave my positive votes :) However, when I was about to start collecting all parts I found myself wondering a few things they don't mention in their solutions, so here it goes:

As the achievement description says, there's a total of 126 car parts: 40 are found in Crimson Park, 40 in Perilous Park (Joao Aden1lson's videos, both parks can be found under Stunt Parks in the menu; 100 HP works just fine), and the remaining 46 are found in the 10 different tracks (ro455BR's videos, 100 HP also just fine).

The parts that are in the tracks are always the same, that is, it doesn't matter if you find them using 100 HP, 200 HP, or 300 HP cars/tracks. Once you find a part, it is "found" in every HP mode. You can also find them in any of the racing modes (champioship, individual races, time trial). I personally preferred the individual races option because it's not as boring as the time trials, but the advantage of either of these modes, as opposed to championship, is that you can pause and see how many parts you have found and how many more you need for that particular track. Also, in the case of the races, it doesn't matter if your bot opponents finish the race, it ends only when you cross the finish line for the last lap, so you have all the time you need if you want to find the parts yourself without using a (video) guide. In the case of the Time Trial option, it's just you & infinite time.

My advice would be to go for this achievement before the 300 HP championship, as you'll certainly need better cars to beat that one, and those better cars become available only after you find their car parts.