\starttext

$y=a x + b$

$y=a {\mkern 1mu} x + b$

\startsetups math:morespacing
    \ordordspacing\textstyle 1mu plus .5mu minus .25mu\relax
\stopsetups

\setupmathematics
  [setups=math:morespacing]

$y=m x+c$

$y=m{\mkern 1mu}x+c$

\stoptext
