Maxxis Extra for Harley MX/Offroad Tire Tube 70/100-17 Made specifically for MX or off-road use Heavy-duty tubes are 1.5 mm thick to be more durable than standard tubes Extra heavy-duty tubes are 2.5 mm thick to offer superb durability in extreme conditions; nearly twice as strong as heavy-duty tube Both use synthetic rubber construction that offers excellent strength and will not allow air to leak like natural rubber