Tires are by far the most important components on a motorcycle. No matter how good your motorcycle is, they will dictate how much engine power will reach the ground, how fast you can go through a corner and they will also determine how fast you can stop your bike.
All of these aspects depend on the amount of friction between the tire and the terrain at any given time which in turn depend on the area called contact patch. The size of the contact patch will vary with the size of the tire. But it will also vary under other circumstances, such as if we mismatch tires and rims sizes.
Let’s dig a little deeper on this subject and compare wide vs narrow regarding some important aspects.
How tire size works
In order to start this discussion, it’s helpful that you understand how tire size works and what all the information on the sidewall of the tire means exactly. The picture below illustrates the most common method in use nowadays. In this article we will stick with the size explanation (items 7 to 10), but if you are interested in understanding the rest of the information (and we hope you are), here is a link to the tire manufacture explanation page.
7 – Indicates how wide the tire is. In this case 190mm.
8 – Indicates how tall the sidewall is by using the aspect ratio. In this case 55% of the width of the tire, so 55% of 190mm which equals to 104,5mm.
9 – Indicates the type of structure/construction of the tire. In this case the tire was built with Radial construction.
10 – Indicates the size of the rim that the tire is indicated for. In this case, a 17” rim.
1. Wider tires offer more grip than narrower ones
It sounds obvious, so let’s put it out there already: if a tire offers more contact with the terrain, then it offers more grip, so technically a wider tire should offer more grip (we will see later that this is not always quite true). When engineers are designing a motorcycle, one of the things they have to figure out is how much grip that bike will need in different scenarios such as riding on a straight line, cornering, accelerating, braking, among others.
Usually, the more powerful a motorcycle is, the more grip will be required for it to function under the different circumstances just mentioned. None of that means that wider is always better though. If a bike is fit with a tire that is too wide, it will be more difficult to lean into corners and it will require more input from the rider in order to keep any line.
Also, wide tires are heavier and the consequence to that is acceleration and braking capacity will suffer with it. Compared to a wider tire, the narrow ones will be easier for handling, but because they have less area, they will suffer if the motorcycle is too powerful and will wear out way too fast; that is why the narrower tires are normally fit to smaller and less powerful motorcycles.
2. Wider tires allow for more corner speed in big motorcycles
The width of the tire will determine the amount of lean angle the motorcycle can carry through a corner but it will not do it alone. When a motorcycle is going through a corner, the centrifugal force that wants to push the rider out of the curve is equivalent to the lateral acceleration created by the motorcycle leaning into the turn.
When leaning on a bike that has wider tires, the contact patch is farther away from the centerline of the tire, so the rider has to lean further and reach higher lean angles. With a narrower tire, the contact patch is closer to the center line and consequently less lean angle is required for the bike to turn.
All of that correlates to how much speed you can carry through a corner, and this is the reason why less powerful motorcycles do not need wide tires. They simply do not have enough power nor the chassis to carry all that speed.
If you are riding a powerful street motorcycle – 1000cc bikes for instance – you will be able to carry higher corner speeds with the wider sport tires fit to it from the factory. In order to do that, you will have to lean further.
If you are riding a smaller motorcycle with less power, you have less speed to carry through the corner and consequently need less lean angle which allows the manufacturers to fit narrower tires to the bikes.
3. Tire size affects suspension behavior due to different weight mass
Unsprung mass on a motorcycle is every component that is connected to the main body via the suspension: forks, rims, tires, brake disc and caliper etc. These are the components that the suspension will have to deal with while the bike is on the move going through corners and any terrain imperfections.
Wider tires are bigger in size than narrower tires, which also means they carry higher mass. If they are heavier, the unsprung mass the suspension has to take care of is also higher. The opposite can also be a problem; if we fit a much narrower tire than recommended, now the mass is much smaller, and this will affect suspension behavior.
Fitting a tire that is much wider or much narrower than recommended by the motorcycle manufacturer can cause problems on the suspension and consequently on the dynamics of the bike because the extra/lesser amount of tire weight was not accounted for by the engineers when defining the specifications of the suspension componentry (forks fluid and geometry, spring factor and geometry etc).
4. The most cost effective tire is the one recommended by the manufacturer
Wider tires are generally more expensive than narrow ones. This is not only because of the extra material, but also wider tires are generally more biased towards specific situations which means the manufacturers can play with different rubber compounds in order to offer proper grip under different situations.
Another factor is that wider tires are normally made for bigger/heavier motorcycles capable of carrying more weight, which makes necessary for the tire to have special construction so that it can also carry all the weight from the motorcycle, the rider and any extra load.
Installing a tire that is wider than necessary will make you spend more on the purchase, but it can also make it necessary for tire replacement more frequently due to uneven wear – a tire that is too wide can drag against the fender wells and wear out the rubber in an unpredictable manner for example.
On the other hand, installing too narrow of a tire will be cheaper at purchasing time, but most likely the tire will wear out really fast because it will be handling more power and weight than it was designed for from the beginning. What all of this means is that both options most likely will cost you more than following the manufacture recommendation for tire appropriate tire size.
5. Wider tires increase friction and weight, leading to higher fuel consumption
Because wider tires will offer bigger contact patches, friction will be higher requiring more power input from the rider in many different situations.
Besides, as mentioned before, wider tires are generally heavier, which means the overall motorcycle weight will also be higher and again more power will be necessary to carry the extra weight. All of these factors together will play a major role in the fuel consumption of your motorcycle – to the worse.
6. Original tire size is the safest option
The tires you install on your motorcycle are the main component when it comes to safety as well. Forget about bigger brakes or more power; the tires are what allow a motorcycle to start moving in the first place and also allow the same bike to come to a stop when necessary. Some of the decisions we make when it comes to tires can greatly increase the risks of riding a motorcycle.
Squeezing a wide tire into a narrow rim will pinch the tire and reduce the patch area. This will also make the motorcycle lean much quicker into the corners which can become an element of surprise for the rider and because of that a safety hazard. This will also reduce the contact area when on a straight line, which is also dangerous in itself.
The other way around is also bad; if you stretch a narrow tire to fit to a wide rim, this will flatten the contact area and make it really hard to lean; if the rider approaches a corner at usual speed, the tire will restrict the movement and the rider will get the feel the motorcycle is fighting with him.
These scenarios can also have influence on how the tire will wear out and in both the most likely to happen will be the “square” wear out, when the center of the tire wears out much faster than the sides – this condition is very common on bikes that do a lot of highway miles. The point here is the safest option is to keep the motorcycle with the original size of tire.
7. Going wider or narrower, use proper rims and spring sizes
Some riders think it is cool to have a big fat tire on the back of a motorcycle; this is really common amongst the cruiser crew, especially the custom ones. Some other riders think it is really cool to have very skinny tires fit to their motorcycle; this is very common in Asia where smaller bikes represent the biggest market share.
If these changes are done just for the way it looks and these motorcycles will not be used under extreme conditions, it is possible to execute the modifications in a safe way – proper rims, suspension (especially springs) and enough space for the tire to move without interfering with other components.
When a tire size is chosen for a specific motorcycle by the manufacturers, its characteristics are directly linked to the motorcycle dynamics. How the bike will accelerate, brake, corner and how the suspension will behave under different conditions.
With a different size fit to it, all of that can be thrown away and become a safety issue. Choosing a different tire size can be done, but it is necessary to pay attention to certain elements and understand the types of compromising the rider will have to cope with.
Generally speaking, jumping one or even two numbers on the tire size can be done without major problems – if recommended is 180mm, it is possible to go 185mm or 190mm; still, for safety reasons, it is necessary for the rider to pay attention to details discussed along this article.
Sometimes a tire for specific use simply does not exist on the recommended size and moving up or down a bit is the only option. Check the manufacturer manual for size recommendation as well as the original rims (they come with their sizes engraved on the sidewall) and remember you are dealing with the most important component of your motorcycle. Ride safe.