BYD is building a large selection of EV's and hybrids aimed at all the segments of the market. I think your general observation on size is accurate. Size and weight equate to cost; smaller, lighter = cheaper to build. So yes, we will probably see cars in all classes literally downsized to keep cost and sale price as low as possible. The Seagull has been a huge hit for BYD based on affordability, it definitely fills a market segment looking for a low cost alternative.
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