Figure with two side-by-side subfigures that is wider than textwidth

Question

I have a 2x2 array of subfigures and the ideal size I'd like them at is a bit wider than the textwidth. I saw this solution for a single figure (Custom margin settings for figure in LaTeX) but am not sure how to adapt it for subfigures.

edit: a 1x2 example of the way I'm building my subfigures

\begin{figure}[ht!]
\centering
\begin{subfigure}[b]{6cm}
    \centering
    \includegraphics[width=6cm]{...}
\end{subfigure}
\quad
\begin{subfigure}[b]{6cm}
    \centering
    \includegraphics[width=6cm]{...}
\end{subfigure}
\end{figure}

Answer 1

You can use a \makebox for each row of subfigures (change the lengths to suit your needs):

\documentclass{article}
\usepackage[demo]{graphicx}
\usepackage{subcaption}
\usepackage{lipsum}

\begin{document}

\lipsum[2]
\begin{figure}
\makebox[\linewidth][c]{%
\begin{subfigure}[b]{.6\textwidth}
\centering
\includegraphics[width=.95\textwidth]{image1}
\caption{a test subfigure}
\end{subfigure}%
\begin{subfigure}[b]{.6\textwidth}
\centering
\includegraphics[width=.95\textwidth]{image2}
\caption{a test subfigure}
\end{subfigure}%
}\\
\makebox[\linewidth][c]{%
\begin{subfigure}[b]{.6\textwidth}
\centering
\includegraphics[width=.95\textwidth]{image3}
\caption{a test subfigure}
\end{subfigure}%
\begin{subfigure}[b]{.6\textwidth}
\centering
\includegraphics[width=.95\textwidth]{image4}
\caption{a test subfigure}
\end{subfigure}%
}
\caption{A figure with four subfigures}
\end{figure}

\end{document}

The demo option for graphicx simply replaces actual figures with black rectangles; do not use that option in your actual document.