It would have a massive effect. Transport (car) emissions are one of the larger - and growing - sources of emissions.
And we can’t hide behind “But the corporations…” because ultimately what they produce gets used by us.
So to answer your question: riding a bike when Global Capital wants you to keep buying cars and pumping oil into them is one of the best acts of defiance you can make
Interestingly, my family subscription more or less halved a few months ago, which I was NOT expecting, but which was very welcome