Are you really looking to limit the speed available to wireless clients, or are you just trying to limit the impact a wireless device can have on the performance experienced by the wired devices? Reserving some external bandwidth as wired-only is a pretty crude way to accomplish the latter.
Any time you have a bandwidth sharing issue, the first step should be to rate-limit the router to just below the modem's speed (thereby preventing the modem's bufferbloat from kicking in) and apply an advanced qdisc to your router's WAN interface (preferably fq_codel if your software is new enough). That will keep latency from going sky-high when the WAN connection gets saturated, and ensure fair mixing of competing flows.
Only if that is insufficient should you move on to more barbaric strategies like overtly singling out certain clients or protocols for special treatment, since those policies are high-maintenance and often prevent the second-class citizens from getting full performance even when the network is otherwise idle.
Any time you have a bandwidth sharing issue, the first step should be to rate-limit the router to just below the modem's speed (thereby preventing the modem's bufferbloat from kicking in) and apply an advanced qdisc to your router's WAN interface (preferably fq_codel if your software is new enough). That will keep latency from going sky-high when the WAN connection gets saturated, and ensure fair mixing of competing flows.
Only if that is insufficient should you move on to more barbaric strategies like overtly singling out certain clients or protocols for special treatment, since those policies are high-maintenance and often prevent the second-class citizens from getting full performance even when the network is otherwise idle.