你的句子是正确的，没有问题，“倍数”是可以修饰比较级的。

The car runs twice faster than that truck.

又如：

She can walk three times faster than you. 她走路的速度能比你快三倍。

Water is eight hundred times denser than air. 水的密度是空气的八百倍。

Edinburgh is five times bigger than Oxford. 爱丁堡比牛津大四倍。

另外，也可以用twice as fast as等：

The car runs twice as fast as that truck.