The appreciation in classic cars—classified by Coutts as those that have been auctioned for more than $500,000 and have been sold more than 10 times—dwarves that of U.S. stocks, which put in a strong performance in 2014.
The benchmark U.S. S&P 500 gained 11.4 percent last year, while the narrower Dow Jones industrial average rose 7.5 percent and the Nasdaq Composite gained 13.4 percent.
Coutts, which is known for holding the account of U.K. Queen Elizabeth, published its "passion investment" index on Tuesday, which tracks the appreciation of some of the most popular and valuable collectibles.
While cars came out easily the winner among passion investments, other strong performers included "Old Master" and 19th century art and coins, which gained 10.7 percent and 9.3 percent respectively in 2014. Other assets in the index included watches, fine wine, stamps and jewelry.
"At a time of paltry interest rates, we continue to see lots of interest from the wealthy in finding somewhere worthwhile and out of the ordinary to put their money," head of financial advice and investment solutions at Coutts, Mohammad Kamal Syed, said in a news release.
"Passion assets maintain their appeal, indeed the majority of passion assets we've tracked have risen over the past 12 months. Aside from the returns, these assets can bring a sense of excitement and the thrill of acquisition is a clear motivation for lots of collectors."