Classic cars grew in value by 9% in 2016, according to a leading price index.
Historic Auto Group (HAGI) tracks the performance of the globe's leading classics across a variety of makes and models.
Classic Ferraris were up 6.4% in 2016
While 9% growth is strong by the standard of traditional investments, it's below the 17.6% gains achieved in 2015, and the 25.1% rise posted in 2014.
Experts have suggested an increase in vehicles at auction was a contributor towards the slow down.
HAGI believes last year's financial uncertainty was also a key reason, keeping many would-be investors watching from the sidelines until the picture clears.
"The market in 2016 was dominated by knowledgeable collectors, rather than financially motivated investors," the company explains.
HAGI adds: "For 2017, the potential rise in global interest rates may have a significant effect on the overall market."
This suggests less investors will be motivated to place their money in classic cars, as traditional investments begin to look more attractive again.
Porsche posted a 9.3% rise during 2016, with Mercedes-Benz classics climbing by 7.5% and Ferraris up 6.4% - a modest return for the usually strong "prancing horse".
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