Why are bikes more stable when travelling quickly?

Can you please explain how a bike is more stable when it is travelling faster. By the principle of relativity, it should be explainable if you take the bike as stationary and the earth moving underneath it, so the only difference I can now see is that the wheels are spinning faster, so the answer must be to do with the spinning wheels? Please could you explain this to me, if possible talking about forces and explaining it from the reference frame taken above. Thanks.