Is Cozumel Rent a Bike new? I didn't run across them when I was doing my bike-rental searches last year. And if they're new, are their bikes new?
Skittl, we rode the path/road/cyclopista you're referring to. It exists north of town and south of the cruise-ship piers--the stretch in between, you're on the road with the cars, but it's not so bad. I rode the Isis bike, mangled pedals and all, on the cyclopista north past the country club to where the regular road ends (and then north up the dirt road some more) and we took our Sombrero (mountain) bikes south past the Iberostar. I would have liked to go to the other side, but the bikes and the heat were beating us at that point. The farther south we got, the more vehicles we saw using the old road/cyclopista. On the north stretch, I didn't see any interloper cars, and for much of the way, it's very much like a suburban U.S. walking/biking path. Even to the south, it's not like it felt dangerous (though you can't take the sobriety of drivers coming from those beach clubs for granted). Beyond that, my best advice is simply to bring lots of water if you're venturing much out of town--there aren't as many OXOs and places to buy quick refreshment as you might think.
Sombrero did give us locks, but not helmets. For places where we were eating outside, we just parked the bikes close by, where we could keep an eye on them. On the rare occasion when we went inside somewhere, we usually managed to find a pole or something to lock to. We did not, however, find a great place to lock up in front of the Mega--so just one of us went in at a time. At night, we carried the bikes up to our room. Coming from a big bike-theft city, we err on the side of caution in these things.
At night, we strapped small dive lights to the handlebars for safety and to see. (The back streets are kinda dark.) If I were to decide to rent a bike like that again, I'd probably also grab my blinky back light and a cable tie or two. I would not even think of riding on Cozumel's sidewalks for any number of reasons. The streets felt safe enough, even in town and on Melgar. The traffic lights are a little different than at home, so we were just really diligent about observing and following them, and paying close attention to rights-of-way on the back streets.
If you're looking at having a bike just to bum around town, the Sombrero bikes are plenty adequate (they also have cheaper cruisers and more expensive tri road bikes--we didn't lay eyes on those). If you're used to riding a pretty new, higher-end bike with really good components in tip-top shape and slick, skinny tires that let you glide along with little effort, you might not find a longer ride on these as pleasurable as you might like--take this from the perspective of someone who's been riding around the last couple of years on a nice little 16-pound road bike, and who is fairly comfortable riding in congested urban areas.
Also, I noticed the Villa Aldora bikes when we stopped in there briefly--they looked to be an assortment of mostly older bikes that would be fine for the short trip to town and back, and it looked like there were plenty of them--it's super nice that they provide them to their guests. It also looked like one could procure cruiser bikes from in front of the Hotel Cozumel--not sure if they're just available to hotel guests or what.
