Android : SMS Manager send mutlipart message when there is less than 160 characters

I write a app which use SMS Manager. I use method sendTextMessage() but it isn't work. Now I am using sendMutlipartTextMessage() and it's work. But it's send multipart message when it is about 60 characters. This is normal? Everywhere I read than should be 160 characters. This is important to me because I must pay more.