Starting in Rama 3 it's a 30 km long ride to Suvarnabumhi airport. The shortest way is by Sukhumvit 77 (On Nut rd). It's mostly quite busy, but after Srinakaran rd, it's mostly better.
The track around the airport is nearly 24 km. There is a large car parking. To enter the track you have to register. You get a bracelet with a chip so that next time you can enter as you want.
The track is nice with the airplanes taking off or landing over your head. Perfect for plane spotting ...
Another road is possible by Krung Thep Krita, Patanakan and Petchaburi rd. But this road is more dangerous for cyclists because it's smaller.