When you use hyperbole like comparing bike riding to a choice of taking poison, then you fail to make your point. Bike riding may not be tzniusdig for a whole bunch of reasons, the clothing, IMO, being the least of them. I think the focus of seeing a woman’s view from the back is more probpematic. I do not advocate for bike riding. I MERELY pointed out in answer to the implied question of why would a woman need to ride a bike, that there could be a very good reason. Maybe she likes the exercise, maybe she cannot afford taxis everywhere (do you actually know how expensive car services are on a regular basis???). It is not for anyone to judge whether or not she can avoid it. The idea is to find tzniusdig ways to do something that in and of itself is not assur.
BTW, apropos of what Aposhitermaidel posted, I also never learned ONE WORD about the so-called “kosher” fit for sleeves. Not one Morah ever told us we should not wear tops made of leotard type material. In fact, they, and all the rebbetzins ALL dressed that way. They wore vests or such over them, but the long sleeves were all close-fitting. Did you never see a turtleneck sweater?