I don't see any option to limit the max speed of a truck in Bing Maps documentation: https://learn.microsoft.com/en-us/bingmaps/rest-services/routes/calculate-a-truck-route
The Azure Maps routing service does however have this feature as documented here: https://learn.microsoft.com/en-us/rest/api/maps/route/getroutedirections See the vehicleMaxSpeed option