Friday Five: Tires
Spend a few minutes assessing your rubber friends.
Let’s start with a bold statement, tires will make a bigger difference to the performance of your bike than anything else bolted to your bike. Run the wrong tires and no matter how good you are or how much you have spent on the rest of your bike, you might be struggling to get the most out of your ride.
Choosing the right tires is an absolutely vital part of setting up any bike. Depending on where you ride, the types of trails you ride and how you ride, you may want to play with tire choice. Some trails will favor having higher volume, deeper tread tires, on others perhaps you will need a little less.
The most essential thing to know is that there is no one tire that is best for every situation. Some tires are exceptional across a wide range of terrains and conditions, but the most optimal tire choice will come from knowing what terrain and conditions you ride in and knowing how different tires feel and work in various conditions.
We could go on and list a lot of tires here, but that won’t help you find your perfect tire choice. Models change, new ones are introduced and ultimately it’s about finding the tire for you and the conditions you will be riding in.
Treads fall somewhere along the spectrum from semi-slick to extremely knobby. Semi-slick treads are intended for hard-packed surfaces because they offer reduced rolling resistance. However, what you gain in rolling speed you will forfeit in traction if the trail surface becomes rougher and conditions become damper. Knobby treads are intended for off-road use, where the tread texture can help improve traction on soft and rough surfaces.
Many treads are unidirectional and designed to be oriented a certain way. Some tires have a tread that is intended either for the front wheel or the rear wheel.
Softer, rougher terrain is more suited to a wider-spaced tread pattern. This gives more edges for traction when braking, accelerating and cornering. It also helps prevent mud and dirt from packing into the tread, which would make the tread less effective. Some very pronounced tread patterns can actually result in less traction, particularly on very hard packed surfaces. The rubber compound used in the tire also plays a role here.
The tread will alter how a tire reacts in certain situations. Some work well under linear forces (braking and acceleration) but personally I like to choose tires on how well they turn. Some tire treads are positive most of the way through the turn, some break loose and then are positive again. Depending on the terrain, either of these can be good. Some riders like to have the bike’s traction break away early so they can initiate a turn, drift and then “hook up” later in the radius of the turn.
Some Maxxis tires have been known to possess a shoulder in the tread that allows a predictable drift. Other tires have a larger zone on the shoulder and knowing when they will catch is a little less predictable. Maxxis Ardents can get a lot of lateral movement, something that—depending on the trail and trail surface—is enjoyable. However, because they have less of an aggressive side knob profile, knowing when they will catch takes more experience.
Your home work this weekend is to figure out what tires suit your trails and how you like to ride them.
The rubber in tires includes additives which can improve wear resistance, but usually at the expense of traction. To remedy this some tires have a dual-compound tread that is tougher in the middle and grippier on the edges.
It might be logical to think that a harder compound tire with a tight tread pattern will be fastest. However, in situations where the trail is extremely rough, rocky, rooty, or damp, traction is sacrificed with a hard compound and tight tread patterns.
Conversely, in situations where the trail is made of dry, hard-packed soil and requires a lot of pedaling, a softer compound tire can mean more drag and more rolling resistance. Know the types of trails you ride most often and get used to how different tires feel and react in different conditions.
If you’re traveling to new places or if you are unsure of what to run, survey other riders for their tire choices. In particular, identify the core locals and see what tires they are running.
An interesting idea on size and pressure
It is commonly accepted that narrow tires with high pressure and a fine tread pattern will roll fastest. However, Peter Nilges, for his graduate dissertation at the German College of Physical Education, Cologne, researched the subject of rolling resistance and what he found was that this isn’t exactly true for mountain bike applications. Nilges measured the rolling resistance of three different tires with three widths and at four different pressure levels on varying conditions – road, gravel and grassy meadow.
Nilges found that on asphalt there is no marked difference between a narrow and wide tire, but while off-road, wide tires rolled more easily. The rougher the ground, the greater the advantage. Nilges then looked at the contact areas of the two different tires and discovered that the areas are nearly equal in size but different in shape. The wider tire’s contact patch is wider, but shorter, meaning the lever the tire has to overcome is shortened.
As for tire pressures, there was similarly surprising findings. On the road the principle that states that a firmly-inflated tire makes for good propulsion is true. However, as soon as you leave the road, reducing tire pressure actually reduces rolling resistance.
The reason for this? Nilges hypothesized that the lower-pressure tire can adapt to the unevenness of the ground more easily, reducing the amount of energy disruption that is caused by the unevenness of the ground. You could say the tire is acting like shock absorbers, preventing the wheel for being moved up and down and horizontal propulsion being turned into vertical movement.
In conclusion, Nilges says that anyone who wants to ride really fast off-road needs to decrease tire pressure. The rougher the ground, the more pronounced the effect. In addition, traction and comfort increase too. Due to their thin and flexible structure, semi-slicks offer the best start-up values for minimizing rolling resistance off-road. With a reduction in pressure, however, the risk of a flat tire increases. And traction with the semi-slick is limited. So the answer, Nilges finishes, to the question of which width is best off-road clearly reads ‘fat tire’ both for superior traction and snake bite prevention.
[NOTE: Link for the study “HOW TO INCREASE YOUR SPEED: ALL ABOUT ROLLING RESISTANCE” BY PETER NILGES.
Tube or Tubeless?
To use inner tubes or to go tubeless, that is the question. Inner tubes are, in some respects, simpler to use and set up. However, they are more prone to flats than tubeless tires. A tubeless system requires a compatible tire and an airtight rim (sealed spoke holes, but with a special airtight valve for inflation). The benefit of this system is far lower chances of punctures, particularly at lower air pressures. The downsides are slighter heavier tires (but lower overall weight compared to using tubes), a little more complexity to the initial setup, and the possibility of ‘burping’ them under heavy corner loading.
UST or Universal System Tubeless is a standard to which some tires and rims adhere. It provides a very secure and reliable fit between the rim and tire bead. Other manufacturers have their own standards too. Some tires and rim combinations can still be made tubeless but sometimes doing so reduces reliability.
A liquid sealant, which hardens upon contact with air is used in tubeless tires to help seal the bead and prevent deflation from punctures. It is essential that the sealant level is monitored and topped when necessary.
Despite being reluctant to trust tubeless setups for many years due to the cost and perceived extra time, I’ve begun to favor this system because of its advantages – greater traction, generally lighter weight and improved puncture resistance. It also doesn’t take long to set up and means much less garage time in the long run.
When using a tube system it might be necessary to run higher pressures to avoid pinch flats, which means traction and comfort suffers a bit. The only thing worse than pinch flats is bike thieves. Tubeless systems don’t completely reduce the possibility of flat tires, but it reduces the chance by a large margin.
We also get a much more comfortable ride because of the lower air pressure that we are able to use. Slightly softer tires conform a little more to the trail so our traction is increased. See above study on tire volumes.