To find out if bikes with larger engines are more dangerous, as is commonly thought, we looked at data from the Department for Transport on two key metrics: number of fatalities and serious injuries by engine size and number of motorcycle registrations by engine size. It's not enough to look at casualties by engine size—one also needs to consider the number of each type of bike on the road because bikes that are more common will naturally be involved in more accidents due to sheer numbers.
Number of Bikes by Engine Size
In 2018, there were 1,265,100 motorbikes registered in Great Britain. Bikes over 500cc were most popular, with the number of bikes over 500cc increasing 6% between 2014 and 2018 reaching 694,000 on the road. Bikes 50cc and under have been dropping in popularity as riders opt for larger engines.
|Number of Motorcycles in Great Britain by Engine Size (thousands)||1 - 50cc||51 - 500cc||Over 500cc|
In terms of proportions, 55% of motorbikes registered in the UK in 2018 were over 500cc, 39% were in the range of 51 - 500cc and just 6% were 50cc or under.
|Proportion of Motorbikes in GB by Engine Size|
|1 - 50cc||6%|
|51 - 500cc||39%|
Bike Casualties by Engine Size
The largest proportion of motorcyclists killed or seriously injured in 2018 was riding a bike with an engine size between 51 and 500cc (the mid-size category). In fact, 49% of those ksi (killed or seriously injured) in a motorcycle accident were riding a bike with a mid-size engine; 42% were riding a motorbike over 500cc and 7% were on a bike 50cc or under.
|Motorcycle riders killed or seriously injured 2017, by engine size||50cc and under||51-500cc||Over 500cc|
Bikes with larger engines do not appear to be the most "dangerous" to ride. The data show there are more bikes on the road with engines larger than 500cc, but more fatal or serious injuries for riders of bikes with engines between 51 and 500cc. In fact, bikes with larger engines had the lowest rate killed or seriously injured (ksi) per thousand registered bikes.
|Engine Size||Casualties (killed or seriously injured)||Registered Bikes (thousands)||KSI per Thousand Registered Bikes|
|50cc and under||395||70||5.6|
For more information on motorcycle safety in general, see our article How Dangerous are Motorcycles?
Interpreting the Results
So are bikes with larger engines actually safer? Not necessarily.
Bikes with larger engines typically cost more money to buy and insure. In order to be able to afford the higher purchase and insurance prices, it's likely that those buying larger bikes are older with more financial wherewithal—and older riders are generally safer riders as they have more experience and are likely to be more sensible/risk averse (e.g., engaging in less high acceleration driving). This is evidenced by the fact that motorbike insurance policies cost less as you age—to a point. As a result, it may not be the case that bikes with larger engines are safer for any given rider—lower accident rates for large-engine bikes could very well be due to a difference in riding styles due to age and sensibility.
Motorbikes with larger engines are likely to be more dangerous for some riders, such as those with less experience or who drive more aggressively.