- Air cooled motorcycles run quieter.
- You’ll tend to see them more on cruisers as most cruisers typically run at lower RPMs then sportbikes, which tend to be liquid cooled.
- Air cool provides more simplicity, representing one less thing which could break or need to be replaced.
- Liquid cooling rads are sometimes fragile, and external or aftermarket oil-coolers can also be expensive and likely to break in a drop. Air cooled bikes may be cheaper.
- Air cooled is also likely more feasible for single cylinders (big thumpers) or parallel twin engines rather than V-Twins, where the back cylinder would remain hot.
- In liquid cooled engines, the circulating liquid evens-out hot spots in the cylinder head. This is better for detonation control and for emissions. The combustion chamber surfaces can be kept hot enough to encourage more complete combustion, but not so hot so as to promote detonation or high NOx emissions.
- Liquid cooling is better for long-term durability since it allows tighter build tolerances.
- Liquid cooled engines transfer the heat to the rad at the front of the bike, making a long ride or a traffic grid lock more tolerable for the rider.
What you’ll want depends entirely on your ride. Sportbike or other high-revving engine, you may want to make sure you’re getting something with liquid cooling. Scooter or cruiser can probably get away with air-cooling. Many people say Harley-Davidson Sportsters never overheat, but if they do get hot, there are always things you can do, such as switching to a full synthetic motorcycle oil, or adding an OEM or aftermarket oil cooler.