I just finished a SS conversion of an old road bike I had and I would like to use it to commute on. It doesn't have the holes to mount a rack on the back so I was going to use the P clips. Now my. question is how much weight would these support? I'm planning on useing a set of panniers to carry a change of clothes and my lunch and about 2L of water. I would be gratefull if anyone. has some insight to share.