I have an 80's Bianchi frame and I am in the middle of rebuilding it. I have checked the rear triangle alignment with the string method. I tied a string from one rear dropout up and around the head tube, down around to the other rear dropout.
I then measure the distance from the seat tube to the string. I measured 32mm on the left side and 36mm on the right.
I know I can adjust the frame as found here, should I? Is 4mm enough to cause a problem riding the bike? Is the amount it is out necessitate spreading the rear triangle?
Also, the bend in the rear dropouts, how do I tell if the angle is correct? I presume the dropout has to be parallel to the centerline of the bike. I do not have any tools to measure this and I really can't afford to buy any. Are there methods to check alignment at home using string, a building square, a tape measure, etc?
Thanks for the help.