Ok first avoid 21st to 27th of Oct as the stretch from west Calder turn all the way to CarnwATH WILL BE CLOSED. POSSIBILITY of bikes skipping through. But not guaranteed.
Not too much traffic heading west even at rush hour. Especially after the Kirknewton turn.
You can avoid the A70 by going through the top of Colinton and on past JK Rowling’s stable. There is then a short section of muddy path then on the road at blinkbonnie which then comes out at kirkbrae in Currie. Little bit of a footer but enjoyable if pootling, not great on road bike.
But if you mean going up to Bonaly then over by pass and round the back it starts well up to the reservoir and is proper road all the way round the reservoirs until you hit a farm road that is not great even on a hybrid. Goes on a fair bit then comes out at the farm and Mount Parnassus where James Thomson the weaver poet used to live. Now a picture framer? I do not see this as road bike suitable.
There is a water mains replacement project at balerno (a different one from the big pipeline from fairmilehead to thriepmuir) this means some delay on the road but not much.
I am guessing you are thinking the old ring road but i fear your best option is to go through Colinton. That main road is also due to close at some point soon which will cause traffic chaos for sure. In general heading west the traffic is lighter but various points of congestion