How to specify B5 in tufte-book

Question

I'm having trouble creating a working b5 layout with tufte-book. According to their documentation, this is supported:

The Tufte-LATEX classes currently only provide three paper sizes: a4, b5, and us letter.

I'm however confused because nowhere it says how we're supposed to change it to b5. I tried \documentclass[b5paper]{tufte-book} but the result has visual flaws (e.g. the title is clipped at the sides, so is chapter numbering, etc.) - it seems like it's the wrong way to do it. Also, the documentation says the b5paper option is unsupported:

The tufte-book class is based on the LATEX book document class. Therefore, you can pass any of the typical book options. There are a few options that are specific to the tufte-book document class, however.

The a4paper option will set the paper size to a4 instead of the default us letter size.

The following book class options are unsupported: 10pt, 11pt, 12pt, a5paper, b5paper, [...]

So - What's the correct way to change it to a working b5 layout?

Answer 1

The b5paper option seems to work fine. Here the showframe facility from geometry (which the class loads) is used to illustrate:

\documentclass[b5paper]{tufte-book}
\title{Title}
\author{Author}
\usepackage{kantlipsum}
\geometry{showframe}
\begin{document}
  \maketitle
  \chapter{A chapter}
  \kant[1-5]
  \section{A section}
  \kant[6-7]
  \chapter{Another chapter}
  \kant[8-12]
\end{document}