Mobile HAM radio antenna tuning (length) to optomize preformance?

I have a yasue FT 2900R radio and a Workman steel wire antenna ~53" long (136-174 MHZ 3db gain, it says Workman V324... The radio (installed in my truck) works but reception in not ideal at farther distances. I have a friend that has a meter and knows how to tune it, but he is out of the country for a while. Can somone provide a rough length of the antenna intil he gets back so i can use the radio.. frequency i use is 151. thx