These look great. I notice how you have the edges of the railing in the backgroud sharp, meaning your panning movement is perfectly aligned (parallel) with the cyclist's motion.
The shutter speed to use kind of depends on the speed of the subject. With cyclists pedalling, maybe a slower speed like 1/30 (or maybe 1/15) would get more motion blur on the legs.
I would think the best panning shot of a cyclist would be a long but slight downhill where the cyclist is seated and pedalling fast. (their head & shoulders is more steady with less bobbing motion compared to uphill riding). This way you try to nail the focus line on the head and their legs convey the movment. Uphill is better for facial expressions.
I first tried to do this at the Sydney2000 Olympics road cycling event (with a Pentax film SLR) and...... failed miserably..... 5 rolls (=$100) of blurry junk.
I tried some panning technique a few weeks ago (albeit with motor racing). What I found worked best was SR
OFF, 1/50 - 1/60 sec for more consistent and 1/30 give better "look" but I was less consistent. Tried 1/15 but this exceeded my abilites.
I was using a 55-300 and a DA70 posted my gallery & "DAzoom club" and "DALtd club"