  We find an explicit presentation of relative linear Steinberg groups
$\mathrm{St}(n, R, I)$ for any ring $R$ and $n \geq 4$ by generators and
relations as abstract groups. We also prove a similar result for relative
simply laced Steinberg groups $\mathrm{St}(\Phi; R, I)$ for commutative $R$ and
$\Phi \in \{\mathsf A_\ell, \mathsf D_\ell, \mathsf E_\ell \mid \ell \geq 3\}$.
