I'd like to make some humble suggestions if the boards are being tweaked:
Consider having an On Road Racing forum and an Off Road Racing forum and tuck them under the existing Onroad/Offroad forums.
My suggestions for naming, and re-order of the boards would be:
Electric On-road
Nitro On-road
Nitro On-road engine (renamed from On-road Nitro engine)
Racing On-road
Electric Off-road
Nitro Off-road
Off-road Nitro engine (renamed from Off-road Nitro Engine Forum)
Racing Off-road