Motocross and off-road tires are often overlooked in the performance stakes. Many think it's easier to get more power with an different exhaust pipe, or some other aftermarket performance product, but at the end of the day, all the power in the world isn't any good to you unless you can get it to transfer to the ground and give you the right traction!
There are also a few common mistakes when buying tires, mostly generated by confusion in sizing and compounds. So, we'll troubleshoot a couple of the common mistakes.
People often think that the bigger the tire, the better the traction they well get in the dirt. This is not always the case. A wider tire may have more surface area, but can also mean extra weight and force the motorcycle to climb out of ruts, as the wider profile grabs the sidewall of the rut and causes an unsettled ride. Putting a tire that's suitable for a 600cc enduro machine on a 125cc motocross motorcycle just may not work very well. The smaller motocross motorcycle will have trouble getting the giant hoop to move and will eventually sap power from the motorcycle while in the opposite, a 125cc motocross tire on a 600cc will just spend the entire time spinning without traction. So how do I know what's the right off-road tire size to get? Well, this is a good question and easiest answered by looking at your owner's manual or talking to a mechanic at a motorcycle shop. Generally speaking, you should be able to look at the tire that you're taking off and just replace if it with a copy, but if someone has owned the motorcycle before you and put the wrong tire on, you could be in trouble.
What do the numbers mean on the side? The numbers on the side are a description of the size of the tire. So, say it reads: '100/100-19'. Here in Thailand we operate on the Metric system (unlike the folks in the USA), so the first '100' is the figure means that it's 100mm, which is the width of the tire. The second figure is the 'aspect ratio' between the width and height of the tire. So, if it reads '100/100' the first figure is 100mm and 100 percent of that is 100mm. So it's 100mm wide, and 100mm high. If it read 100/80 it'd be 100mm wide and 80mm high. Not difficult, right? The final figure denotes the size of the rim that the tire is better suited to; ie 100/100-19 means it belongs to a 19 inch rim. In Thailand we sometimes also get confronted with tires that are not based on the Metric system – but in that case the numbers mean the same only in inch's.
Why do motocross motorcycle have 19 inch wheels and the off-roaders 18 inch wheels? 19-inch tire generally have a shorter sidewall or profile, which keeps the tire firmer and offers less flex, which is better for MX. IT also means it's less forgiving and harder to change and, with less sidewall, they are more prone to flats. The 18-inch tires have more profile or sidewall, offer a softer ride and take impact from rocks and roots better. They are also easier to change.
The choice of tread patterns for your motocross tire is pretty simple. The softer the ground, the more open the tread pattern is going to be. This lets the tire scoop the surface and act almost as a paddle, allowing better traction for you. It also means that the mud/dirt is less likely to pack-up in the tire and it disperses it easier. A mud-loaded tire doesn't do a good job of getting the power to the ground.
For hard packed surfaces, the knobs get closer together. This means the contact patch between tire and dirt is increased and as it's not loose, it allows the maximum grip as the tire sticks to the hard surface. Think about riding on the road – a road tire's goal is to get as much contact area as possible. If you ride on the road with knobs, it's like trying to ride a unicycle on ice, as there is a minimal amount of rubber touching the surface.
Intermediate is a mix between the two: a play-off between an open and closed pattern while toying with different compounds.