Why do illumina forward reads have better quality than the reverse reads?

Question

[ali.shojaee.bakhtiari]

I have noticed that when both forward and reverse reads from a sample are present, the forward reads tend to have better read qualities, why is it so? What is the deciding factor?

[fanli.gcb]

I've always thought this had to do with the imaging as your clusters are a bit fuzzier by the time you get to R2. Whether this is due to additional amplification or the longer amplicons, I'm not entirely clear on.