Speed Limit 

Keep to a speed that is safe and comfortable. Gravel roads have a speed limit of 80 km/, however Some severely corrugated sections need even lower speed. Always drive at a speed that allows you to stop easily for any hazards.
Speed limits in Namibia are 
as follows:
Tarred roads 120 km/h  
Gravel roads 80 km/h
Urban areas 50-60 km/h

Gravel Roads 

When driving gravel roads we recommend reducing your tyre pressure. Your vehicle will have more traction with a low tire pressure since you have a larger contact area with the ground.This will also reduce the possibility of damage to your tyres. Remember to reflate your tyres when you return to the tar.
Dirt & Gravel Roads 1.8 kpa
Soft Beach/Sand 1.2-1.5 kpa

Water Crossings

Always assess a water crossing before continuing. Walk through and check out the crossing, measuring the depth and checking the condition of the bottom. Even shallow crossings can hid​e tyre-damaging debris or deep holes. As a general rule we recommend avoid driving through water if its deeper than the center of 
your wheels.