The book was about a man who would be surgically altered to investigate different planets, and live with the alien beings on them. He would learn about them, and their social/linguistic behaviours. On one planet he became a being that would curl into a ball and roll. On another, he became some type of lizard-type thing that had a pyramidal structure sticking out from it, the purpose of which he did not know. It's not a recent novel, I probably read it 25 years ago. There were at least two or three different life forms he was altered to be. At the time I was reading a lot of Heinlein, Pohl, and Poul.
The protaganist is Xavier William Lennox. He is an author of alien travelogues and undergoes surgical modifications to fit in with the aliens. When we first meet him he is on a world of aliens called Fireflies (he's discovered and tortured and mutilated and barely escapes with his life - it's a dangerous profession! :-).
The aliens you mention are indeed called Wheelers and live on the planet Tamerlaine. Lennox goes there on behalf of the Department of Cartology to try and assess whether they are sentient or not. This matters because if they are their planet cannot be settled by humans.
However I can't find any mention of a lizard like race with a pyramidal organ. The Fireflies are avian with vestigial wings, but a pyramid is a central part of their religion. Could this by what you're remembering? The other races Lennox becomes are Singers, which are vaguely insectoid, and Hawkhorns, which are somewhat avian but massively built.
The was published in 1994 so it isn't quite 25 years old, but it is otherwise a perfect match to your description.