Lynn and Ron,
While out road biking this weekend, I thought of this thread. I've a mild deviated septum and sinus conditions so I may not be the best candidate for breathing through the nose.
But I'm here to tell ya, that my demands for breath volume during extended periods near the upper limits of heart rate require me to breath via my mouth. Cycling coaches teach the "belly breathing" technique where the sternum is expanded to inhale. It seemed to me that the body/head/neck position when road biking seems to contract the nasal passages.
Lynn, do you use nose breathing on extended rides?
Mike
Hi Mike
I don't think about how I breathe on bike rides. Unless I'm gasping up a hill.
I commiserate about your nasal issues. It seems that the vast majority of humans have deviated septums ( according to my ENT). I am no exception.
And with a life time of allergies, my sinuses are pretty swollen too. To the extent that when I was in yoga class, breathing in and out of my left nostril was an impossibility.
Ron/Mike, have you guys seen an allergist?

Seriously!
I finally admitted I had a problem. Went to allergy rehab. Went from weekly meetings initially and am now down to monthly meetings.
It took a while to achieve the monthly meeting status, but I am happy to be on the allergy wagon. (aka maintenance)
REally seriously, most sinus issues are allergy related. Testing to determine your allergies is relatively easy. Taking allergy desensitization injections is a bit of a committent.
It has made a real difference for me and my sinuses are in much better shape.
MUCH LESS nasal dripping while biking!!! And can breathe thru both nostrils now.
Lynn