How can I get my spoke dimensions without knowing the dimensions of the wheel? I would like to change 4 of my spokes on my back wheel. The trouble is that I dont know the model of my bike nor do I know if that wheel is original, in order to look up the dimensions of the spokes. Here are the dimensions of the tire though if that is to any help:

What would be your recommendations in my case? I am not very proficient at bikes, so please be easy on me :)
Get one of the spokes out ans measure its length. It is a primitive method, but by far the simplest one. Less accurately, you could try to measure it on the wheel and account for the hidden part in the nipple, but I would not recommend it.