If you drive where the roads are smooth, without potholes, or speed bumps, or other pavement irregularities, there’s probably not much difference. When you encounter holes in the road, a scooter’s smaller tires can be deflected more easily, because they generate less gyroscopic effect. Also, a motorcycle’s larger tire will roll over some holes that a scooter tire will fall into, which can cause a strong jolt to the suspension.

Other differences have more to do with (some) motorcycles having more power and greater capacity for speed. That becomes an operator issue; if you go 60 mph on two wheels and hit something, you’ll probably die. If you hit something at 120, you’ll almost certainly die.
posted by Kirth Gerson at 8:17 AM on August 27, 2006

Dangerous for whom? Safety is usually framed in terms of risk for the rider/driver, but it’s equally valid to consider risk for other road users.

In terms of risk for the rider, you may find these USENET threads informative: Thread 1. Thread 2.
posted by Busy Old Fool at 8:23 AM on August 27, 2006

Motorcycles are about 16 times as dangerous per passenger mile.

That being said, not all motorcycle accidents are created equal. The Hurt Report, while older, studied many of the causes of motorcycle accidents. You can be much safer if you avoid riding at night, after drinking, and avoid speeding, these being prime factors for single-rider accidents. For multiple-vehicle collisions, and you can bet motorcycles lose at these, you can wear very bright colors, and use headlight modulators and flashing brake lights to help cars see you.

The best thing to do, if you are interested, is take a course like that offered by the Motorcycle Safety Foundation. Statistics show that people who learn to ride through a course like this, instead of being self taught, have a significantly lower accident rate.
posted by procrastination at 8:53 AM on August 27, 2006

Oh, motorscooters. I would suppose many of the same statistics apply.
posted by procrastination at 8:57 AM on August 27, 2006

if you go 60 mph on two wheels and hit something, you’ll probably die. If you hit something at 120, you’ll almost certainly die.

Make no mistake, the thing that will kill you while riding on two wheels is the brain-dead driver crossing paths with you, not your machine’s ability to go fast.

It’s my belief that a motorcycle is safer than a scooter because of its ability to accelerate away from danger. For example, if a car is entering my lane, 99% of the time I will go full throttle.

Hitting the brakes may cause someone behind me to run into me. I probably don’t have time to look behind me (either with the mirrors or by turning my head). But I can see in front of me, and my motorcycle can out-accelarate most cars by quite a bit.

I’m not sure you have that same exit strategy on a scooter. That means you have to trust the brain-dead driver behind you is paying attention. No thanks.
posted by letitrain at 9:30 AM on August 27, 2006

One other observation is that motorcycles have better handling than scooters. So you are in a better position to avoid an obstacle on a motorcycle than a scooter. In certain situations this may save your life.

Motorcycles are about 16 times as dangerous per passenger mile.

That’s a little misleading, because your chances of dying while riding a motorcycle are still very very low. To put it into perspective, the probability of dying while on a bike is 0.000000334 per passenger mile, while for cars it’s 0.000000013. The point being is that 16 times a really small number is still a really small number.
posted by epimorph at 9:50 AM on August 27, 2006

… so if you drive, like, 3 million miles, you’re dead meat for sure.
posted by reklaw at 10:15 AM on August 27, 2006

I don’t have any fancy statistics to link to, but a week ago my husband was hit by a car on his big Yamaha scooter (250cc) and was lucky to get away with only bumps, scratches and a broken ankle. The scooter itself is a complete wreck.

leiitrain has it completely right I’m afraid. It’s the drivers who don’t care that are the problem. So whether you ride a 50, 100 or 250 cc scooter you need to be aware that other drivers probably aren’t going to be paying attention to you as much as you are to them.

procrastination as some good suggestions as well, and I think they apply just as well to scooters as to motorcycles.

Here in Japan there are a lot of scooters on the road. The smaller scooters seem to get in less trouble than the bigger ones as they can sneak right onto the side or the footpath even in trouble.

In our personal post-accident review we decided not to invest in another 250cc scooter but to go down to 100cc (which is much smaller but still has some accelaration leeway), no more pillion riding, and definitely to up the protective gear. As the Doctor who treated my husband said – wearing a helmet really did prevent his brains from being leaked over the road.