The Ins and Outs of Bike Tire Pressure
Are you as pumped up as we are about inflating tires?! Okay, now that that’s out of our system, let’s get started.
Unlike their automobile counterparts, bicycles don’t come with a dashboard warning light letting you know when your tires aren’t properly inflated. As convenient as this would be, it would also be highly impractical for a slew of reasons that we won’t get into here. Suffice it to say that it’s up to you to find that Goldilocks zone between over- and underinflation when it comes to your family’s two-wheelers.
It would be an oversimplification to say that less air offers a more comfortable ride and more air makes you go faster. While this is true in many instances, the fact of the matter is that proper inflation for optimal performance depends on the individual rider and his or her bike. Today we’ll break down the key things you need to know about tires and how to give them the best bounce for your buck.
Anatomy of a Bicycle Tire
Outer Tire
Despite their basic appearance, tires are more than just giant rubber bands that fit around your wheel rims. Three main components work together to give tires their strength and shape.
- Beads: The two edges, or beads, of the tire sit on the wheel rim and are made of thin steel or Kevlar hoops. These don’t expand during inflation, therefore maintaining necessary contact with the rim.
- Cords: Woven between the beads are cloth cords. Mostly nylon, cords are essentially the body of the tire. If you start to see these through the rubber, that means it’s definitely time for a new set.
- Rubber: The outer rubber casing is the protective layer of the tire. The area that comes into contact with the road, dirt, or any other surface is called the tread. Like visible cords, low tread signals a need for replacement asap.
Inner Tube
People sometimes forget that the knobby rubber around the wheel isn’t the only part of the tire system. In fact, it’s not even the part that holds the air, on which the entire concept of a “tire” is based. This job goes to an airtight, doughnut-shaped, rubber tube that lives within the protective outer layer. Tube thickness can vary, but generally speaking we’re talking about 1mm or so. This is enough to keep it light but still airtight, as well as less susceptible to puncture by rougher patches inside the outer tire.
Although tubeless tires are hitting the market, these are little more complicated and probably not something you’ll need to worry about at the moment, particularly for your kids. In other words, a topic for another day.
Valve
The other visible piece of the tire system is the valve, noble gatekeeper of the airflow. If the Boy Scout in you always likes to be prepared by keeping backup inner tubes in your garage, just make sure you get ones with the right valve for your ride. You’ll find two main types at the bike shop.
- Schrader (aka, “American”): Thicker and flat-ended, Schrader valves feature a central pin inside an outer casing. These are the more common of the two and are used in less expensive bikes and mountain bikes. Most cars also sport Schraders.
- Presta (aka, “French”): Presta valves are thinner than their Schrader cousins and feature a locking nut on top to add or release air. Unless you’re rolling with a higher-end road bike, you’re probably not going to run into these guys very often.
Pound Per Square Inch (psi) for Bike Tire Pressure
Pound-force per square inch — more commonly referred to as pound per square inch — is a 700-year-old unit of measurement (give or take a century) used by the imperial and US systems. By definition, psi is the pressure resulting from a force of one pound applied to an area of one-square-inch. Pretty self-explanatory.
Pressure can also be measured in bar units. But, bar gets into crazy metric stuff like pascals and other things most people have never heard of, let alone use regularly. It’s also not accepted in the International System of Units. So, unless you specialize in niche pursuits like meteorology or international scuba diving, or just really like bar for some reason (in which case, convert from psi here), feel free to skip this for now.
Anyway, every tire has a recommended psi printed on its side close to where it touches the rim. This is usually written as a range (for instance, “90 to 115 psi”) since there are reasons why you’d want to be on the higher or lower end, which we’ll get into shortly.
Basic rule of thumb if your tires happen to not indicate a recommended pressure: pump them up until they’re firm but still slightly squeezable. Alternatively, there are generally-accepted ranges based on bike type:
Road Bikes
Road bikes and tires are built for speed over smooth surfaces. Higher air pressure lets them roll easier and faster. A typical range for these would be between 80 and 130 psi, although racers can sometimes go as high as 160 psi. Quick tip if you’re caught inflating a road tire without a gauge and need to ballpark it: at 100 psi, a tire can barely be compressed with your thumb.
Mountain Bikes
Unlike roadies, mountain bikes are flying over loose, bumpy terrain. Tires with too much air lead to too much bounce, making for a jolty ride. Lower pressure helps with shock absorption while also giving you more traction since more of the tire comes into contact with the ground. MTB manufacturers recommend between 30 and 50 psi on most of their bikes since this is a nice balance between on-road (closer to 50) and off-road (closer to 30) riding.
Other Bikes
Hybrid bike tires require pressure levels between those of road and mountain bikes. This is usually in the 50 to 70 psi range. Kids’ bikes have the lowest recommended inflation, typically 20 to 40 psi. Keep in mind that these are called “recommendations” for a reason, though. A number of factors go into the inflation process beyond just your style of bike.
Which leads us to…
Other Bike Inflation Factors to Consider
Because nothing in life is ever as simple as it should be, we’ve included a few more things to ponder when it comes to making sure everyone’s tires are in good shape for their next ride.
Weight
As a general guideline, more weight = more pressure. Whether you’re competing in the Tour de Whatever or shredding up the backcountry, heavier riders should use a higher psi than lighter ones to see the same performance in their tires. For perspective, someone weighing in at 200lbs will probably want to pump in around 20 more psi than someone who’s 160. There’s no real slide rule for this, so just play around with the pressure and see what feels best for you. Also keep in mind that rear tires tend to carry more weight than those in front, so adjust accordingly as necessary.
Temperature
We know through physics that temperature affects air pressure. At least, that’s what we’re told in high school, ergo it must be true. So, all else being equal, people biking in Miami in August are going to have higher pressure in their tires than people biking in Boston in January. In addition to weather, sustained deceleration using rim brakes generates friction that can increase temperatures inside the tube significantly. Fortunately, they also cool off relatively quickly, but it’s something to keep an eye on during long descents. It may also be worth mentioning to your burgeoning roadster as he or she is learning the basics of hand braking.
Overinflation vs. Underinflation
In short, don’t do either. If you overinflate, you run the risk of blowing the tube either while pumping or while riding due to sudden or constant impact. If underinflated, the low pressure could cause pinch flats. This occurs when the tube becomes squeezed between the rim and tire casing by hitting a bump with an underinflated wheel. Not only does this damage the tire, it can also hurt the rim. Plus, flat tires slow you down and make you pedal harder, which is just no fun.
Frequency
“How often should I inflate my tires?” is a common question among many casual bikers. The answer depends on how often and how hard you ride. Some people break out the pump every few days, others once a week, and still others even less regularly than that. Even if you or your kids have left your wheels in the garage for months, air tends to seep out slowly, anyway. Therefore, as a bike-safety best practice, it’s certainly never a bad idea to check your tires before each ride, especially if it’s been a while.
Bike Pump Options
Floor pumps are the pro’s choice. The good ones have gauges, which eliminate 1) the need to switch back and forth between a pump and standalone gauge, or 2) if you’re really lazy, outright guesswork. It may be tempting to simply use the air compressor at your neighborhood Exxon, but these are less than accurate and can often overinflate your tires (it’s a gas station, they’re meant for cars). For serious riders whose circuits take them far from home, a small hand pump can help you change a flat on the fly. Carbon dioxide inflators accomplish the same thing if you’re an air-in-the-can kind of guy.
So there you go, the ins and outs of basic tire inflation in a nutshell. Clear as mud, right? Don’t worry, the nice thing about pumping your tires is that there’s room for error — as long as you follow these guard rails, that is. You and your kids have free rein to experiment to your hearts’ content, so figure out what feels most comfortable based on your particular cycling style. You’ll get a feel for it over time. Like, literally.
Originally published at spokester.com.
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