TOKYO: Toyota Motor Corp looks set to be hit the hardest among Japanese exporters by the dollar’s tumble against the yen, having assumed what now appear to be the riskiest currency rates for the rest of its business year.

Toyota, the world’s biggest automaker, has assumed an average dollar rate of ¥90 for the October-March second half, compared with ¥85 at Honda Motor and Nissan Motor.

The dollar yesterday sank to a 14-year low of ¥86.29 with exporters getting no reassurance from Japanese authorities, who repeated they had no plans to intervene to prop up the dollar. While the euro’s relative firmness presented some relief, shares in exporters fell across the board to push the main Nikkei average down 0.6 percent to a four-month closing low.

Toyota lost 1.2 percent, slightly more than falls of 1.1 percent in Honda and 0.5 percent in Nissan, but better than Mazda Motor Corp, which fell 2.1 percent. The transport sector subindex lost 1.2 percent.

“Carmakers that issued big profit warnings last year have set cautious forex assumptions this time, so roughly speaking the current rates are within expectations,” Aizawa Securities auto analyst Toshiro Yoshinaga said.

“But there are views that the dollar could sink even further in 2010, to the 70s (yen), and in that sense Honda and Nissan, which are relatively strong in emerging markets, are in the winning camp,” he said.