Adjust the output width of R Markdown HTML output

Add this at the start of your document:

```{r set-options, echo=FALSE, cache=FALSE}
options(width = SOME-REALLY-BIG-VALUE)
```

Obviously, replace SOME-REALLY-BIG-VALUE with a number. But do you really want to do all that horizontal scrolling?

Your output is probably being wrapped somewhere around 80 characters or so.