The 22-year-old Calgarian has emerged as another Canadian medal threat alongside teammate Alex Gough, but needs to give gravity more of a helping hand.
"If you went tobogganing on a hill, the big kid would always beat you," McRae said Sunday at the Canadian luge championship.
"As a gravity sport, the heavier you are, the faster you are, just based on physics."
McRae's breakout season in 2013-14 included her first career World Cup medal and a fifth-place finish at the Winter Olympics in February.
Gough and McRae slid to second and third in Altenberg, Germany, in January. Gough was fourth and McRae fifth the following month in Sochi, Russia.
The German gold and silver medallists in Sochi were taller and heavier than the Canadians. Natalie Geisenberger is six feet, Tatjana Huefner is just over five foot eight and both women are almost 170 pounds.
At five foot seven and 138 pounds, McRae joked with reporters in Sochi about eating a lot of steak before the 2018 Winter Games.
She needs that fuel to take into the weight room. McRae says she managed to gain a couple of pounds over the summer.
"My two biggest challenges are the start and gaining weight," she said Sunday. "Eat a lot of food and go to the gym of course."
More muscle on McRae's slight frame serves two purposes. She'll have more power pushing and paddling out of the start hut if she's stronger in her arms, shoulders and back. The additional weight of muscle is a gift to gravity.
"We talk about moving muscle mass," Canadian coach Wolfgang Staudinger explained. "Build muscle mass because it's heavy and muscles move. It makes you quicker at the start."
Gough, who is also five foot seven and weighs 154 pounds, says there is an ideal body type in women's luge.
"When you look at physics, the most aerodynamic shape is almost a teardrop shape," she said. "That's the way water falls because it's the most aerodynamic.
"When you look at the women that are typically are good sliders, they tend to be curvier girls with hips. Kim and I are not as big as the German girls, but we do have that shape.
"You don't want to be carrying a bunch of extra mass. That's not practical because you have to pull it (at the start)."
Muscle mass is just one of several elements in sliding fast. Size and strength can't overcome a slow start, poor piloting or a sled that isn't set up for track conditions.
"Kim is blessed with a lot of feeling," Staudinger said. "She handles the sled well. It minimizes friction on the ice and that gives it velocity necessary to be where she is at now.
"That's her big advantage. Alex has the same features and Kim is in her footsteps. They are not that far apart anymore. Competition creates performance and I'm very pleased to have those together in the same league now."
With a pair of world championship bronze and two gold among her 17 career World Cup medals, Gough is the most decorated luger in Canadian history.
The 27-year-old is also the lead-off slider of the relay team that has claimed world championship medals and finished fourth in Sochi.
Gough has shown McRae the path to the podium. McRae is now breathing down Gough's neck in training and domestic races.
Gough claimed her seventh Canadian women's title Sunday at Canada Olympic Park less than a tenth of a second ahead of runner-up McRae.
"I was nervous all week. I thought this might be the week where Kim finally takes over," Gough said. "I didn't have a great week of training and I was behind her.
"We're going to continue to push each other. I think it definitely is to our advantage and the team's advantage to now have two women athletes who are really fighting for those top spots."
McRae has the heavier competition schedule of the two until December. Gough is currently taking a full course load in first-year engineering, so her first World Cup isn't until Dec. 12-13 in Calgary.
She'll travel with the Canadian team Thursday to Sigulda, Latvia, for training at the track hosting the 2015 world luge championship.
Gough will return to Calgary and her studies while McRae races the season-opening World Cup in Igls, Austria and the second stop in Lake Placid, N.Y. Gough intends to race the remaining World Cups and the world championship in 2015.
Arianne Jones was third in the women's race Sunday. Veteran slider Sam Edney won his seventh Canadian men's title on a snowy track ahead of fellow-Calgarians Mitchel Malyk and John Fennell in second and third, respectively.
Canada's doubles team of Tristan Walker and Justin Snith, who were also fourth in Sochi, were the lone entry in the national championships.
McRae was born in Victoria and moved to Calgary at age five. After taking up luge in 2004, she attended the National Sport School where athletes pursue their high school education and high-performance sport.
Finishing seventh in the 2013 world championship at age 20 was a hint of her potential. But McRae's rise through the ranks last winter was rapid.
"It was quite a springboard for sure," she said. "From the beginning of the season I went from being last in a couple of World Cups and ended up fifth (at the Olympics), so I want to continue that upward swing."