If you constantly smell gas, you probably have a leak in the fuel system. This is a potentially dangerous problem that should be repaired immediately. Burning resin or an acrid chemical odor may signal overheated brakes or clutch. Check the parking brake. Stop and allow the brakes to cool after repeated hard braking on mountain roads.
Light smoke coming from a wheel indicates a stuck brake.
The vehicle should be towed for repair. A sweet, steamy odor indicates a coolant leak. If the temperature gauge or warning light does not indicate overheating, drive carefully to the nearest service station, keeping an eye on your gauges. If the odor is accompanied by a hot, metallic scent and steam from under the hood, your engine has overheated. Pull over immediately.