Shockwaves from a drop in Chinese car demand are reverberating in Wolfsburg, Germany and Detroit, Michigan, where VW (VOWG_p.DE) and General Motors (GM.N) are feeling the effects of a slowdown in a market that has been their big profit engine. Both Volkswagen and GM are heavily exposed to China, which remains a growth market, but last week cut its 2015 forecast for vehicle sales. Barclays downgraded GM’s stock to “equal weight” from “overweight” on Thursday, saying it was likely to face the sharpest of the China headwinds among the U.S. autos and auto part makers it covers.