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NASCAR driver Angela Ruch will be competing in the most important race of her career next weekend ... and it all has to do with her awesome truck design and the story behind it!

The man who designed the wrap for her #44 truck is her nephew, 19-year-old Eric Erdman, who was diagnosed with advanced brain cancer in 2016.

The condition is terminal -- but Erdman has made the decision to use whatever time he has left to help children battling similar obstacles.

His story is incredible ... and he talks about his life experience in the video below.

Erdman created his own foundation, Give a Child a Voice, to help children dealing with tough medical conditions, bullying and abuse. Through his organization, Erdman has helped renovate several local gyms because he feels physical activity has helped him through the dark times.

Which brings us back to NASCAR Truck Series driver Angela Ruch ... who takes the track for the Ford EcoBoost 200 NASCAR Race in Miami on Nov. 15.

Ruch tells TMZ Sports she wants to do everything she can to help Erdman and his organization -- so she gave him carte blanche to design the wrap for her truck.

Erdman's goal is to raise $300k as part of his "Give a Child a Voice Fitness Center Give-A-Way" (click here for the GoFundMe page) ... and Ruch feels the exposure at the NASCAR race will go a long way.

TMZ Sports spoke with Eric about his aunt getting involved, and he couldn't be more grateful for the gesture.

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"It's amazing. I'm shocked and I love her so much," Eric tells us.

"Don't tell my other aunts, but she might be my favorite just to tell you straight," he joked. "It's truly phenomenal what my Aunt Angela's doing, it's unbelievable. I'm speechless."

Doctors told Eric back in August he has 6 months to live ... but says his diagnosis won't keep him from helping as many people as possible.

"Some people may say 'Cancer, it's awful'. I get that. But, my life, cancer has been the best thing to ever happen to me."

Angela tells us she's honored to be able to use her platform to share his message -- saying, "For me, to be able to support Eric in any way, shape or form that I possibly can, I'm all about."

"I'm so thankful and honored that Eric would even look to me to begin this opportunity to even put his logo on the truck at Homestead. I'm so proud of that young man and words cannot describe the tone that he's setting for so many kids growing up."

Angela says she plans to continue to help Eric every step of the way ...even after the checkered flag is waved.