With a top speed of 85-90 mph depending on the motorcycle’s weight, the 250cc engine typically found on bobbers makes them perfectly capable of highway speeds. It doesn't matter if traffic around you is going 75 mph, you'll be able to keep up without the engine complaining too loudly.
However, the 250cc engine’s small displacement means that you’ll really have to work the engine if you want to stay at 80-90 mph for long. You’ll be near redline all the time, and the vibration from the engine may get uncomfortable.
You really need to work the transmission – both up and down shifts – to keep the momentum going. You have to work to stay at highway speeds, but most riders say it's completely doable on a 250cc bike.
Still, if you plan to do a lot of highway riding I recommend getting a motorcycle with a larger engine. A 300-350cc bike will be much less stressful on the open highway.
