It might be a basic thing, but being able to pump up your bike’s tyres is an essential skill as a cyclist. A lot of you will already know how to do this, but for those who don’t, the different valve types, pumps and more importantly what pressure to pump your tyre to can be a bit overwhelming. Let us guide you through the process.
Why should I care?Pneumatic tyres were invented to get over the bone-jarring ‘ride-quality’ of solid wheels. The air inside acts as a spring, providing suspension for you and allowing the tyre to conform to the terrain providing better traction and grip. Pumping up your tyres is a quick job that can easily improve your enjoyment while riding. Running the wrong tyre pressure will negatively affect the way that your bike rides and can also make your bike more prone to punctures.
How does my tyre hold air?If you’ve never repaired a puncture before, you might not have considered how your tyres hold air inside. The vast majority of bikes will use an inner tube — a doughnut shaped tube that sits inside the tyre, with a valve for pumping it up that you see on the outside. The tyre, when inflated by the tube, is what grips the ground and provides protection from punctures. You may have heard of tubeless tyres, which forgo a tube and use a special rim and tyre to seal air without the need for a tube. These usually require tubeless sealant inside, which is a liquid that plugs any points where air is escaping. Tubeless tyres are more commonly found in mountain biking, but the technology is migrating to road bikes. The tubeless sealant also plugs punctures, and no tube means a much lower risk of pinch flats — that’s when your inner tube is pinched by the rim, causing a puncture. Tubeless tyres can therefore be run at lower pressures than those with an inner tube setup, for improved comfort and traction. At the very high end you also get tubular tyres — essentially a tyre with the tube sewn into it but you probably don’t need to worry about those for the moment.
Inflating your tyres to the correct pressure is an essential part of bike maintenance. Oli Woodman / Immediate Media
Running your tyres at either too high or too low a pressure can be potentially dangerous as well as impact on the handling of your bike. We’ll discuss later what the correct pressure is, but for the moment let’s look at possible problems. If you run your tyres at too low a pressure the tyre can wear prematurely. Excessive flexing in the sidewall can lead to the casing cracking and the tyre becoming fragile. This could eventually lead to a blowout. Excessively low pressures also increase your susceptibility to punctures and may even result in your tyres literally rolling off the rim if you corner at speed (the pressure inside holds your tyre on the rim).
An under-inflated tyre will rob your efficiency and leave you susceptible to annoying punctures. Oli Woodman / Immediate Media
Damage can also be caused if the tyre deflects all the way down to the rim. This can result in dents or cracking, potentially compromising your wheel and resulting in an expensive replacement. Conversely, a too high pressure could result in your tyre blowing off the rim with explosive consequences. That pressure can also squeeze the wheel, because if it’s too high the compressive force on the wheel can be too high. In terms of handling, a low pressure can result in compromised handling with the tyre squirming under load. Your bike will feel difficult to control, slow and sluggish. A too high pressure can result in reduced grip and a harsh ride, leading to fatigue and in turn impacting handling in its own way.
Why is my tyre flat?There are two likely reasons why your tyre is flat. Either you have a puncture or your tyres have just deflated over time. If you have a puncture, we’ve put together a comprehensive guide on how to fix a puncture. Glueless patches are great for a quick fix, while a more traditional kit is a versatile option when you have a bit more time. All tyre systems will leak air slowly because tubes aren’t completely airtight. For example, standard butyl tubes hold air fairly well compared to lightweight latex tubes, which leak comparatively quicker. Even tubeless setups will slowly leak air. Old tubes will leak more air than new ones, so if yours haven’t been replaced in a while that may be worth looking at. Less likely, but also a possibility (especially on older tubes), is that the valve is no longer sealing properly. The best way to check what’s going on is to try pumping up the tyres. If they hold air then there’s likely nothing more you need to do. If they don’t, then you likely have a puncture. And, if they leak air slowly overnight, either you have a slow puncture or simply an old tube that needs replacing.
What valve type does my bicycle have?The first thing you’ll need to know before pumping up your tyre is what valve type is fitted. The valve is the key part that keeps air in the tyre, but also lets you inflate (or deflate) the tyre.
The Schrader valve is also used for car tyres. Oli Woodman / Immediate Media
Schrader valves are more common on lower-end bikes and, in the past, mountain bikes. You might recognise them from your car tyres. The valve assembly is a hollow tube with a sprung valve that closes automatically and screws into the external body. A pin extends up from the valve and is usually flush with the end of the outer tube. It can be depressed to let air out. The dust cap on Schrader valves in an important part of the design that can help fully seal the valve if it is not completely air-tight. It essentially provides a secondary ‘backup’ seal. The sprung design of the valve is a little susceptible to contamination from dirt or grit so it’s important to protect it too.
Presta valves such as this one are longer and narrower than the Schrader type valve. Oli Woodman / Immediate Media
You will only find Presta valves on bicycles. They originated on road bikes where the narrower valve (6mm vs 8mm for a Schrader) meant a smaller valve hole (typically the weakest part of a rim) on narrow road wheels. Nowadays they are seen on both mountain bikes and road bikes. Rather than use a spring, the valve is secured with a nut that holds it closed, though the valve itself is sealed ‘automatically’ when pressure inside the tyre pushes it shut. With a Schrader valve you can simply press the pin to release air, but with a Presta valve you first have to unscrew the little locknut. Don’t worry about the nut coming off the end of the valve body as the threads are peened to stop that happening. There seems to be myth that Presta valves deal with high pressures better — this probably isn’t true considering there are Schrader valves that can withstand many hundreds of psi (way more than you’ll ever need in your tyre).
Presta valves are definitely a little more delicate than Schrader valves, it’s quite easy to knock the threaded internal valve body and bend or break it, so a bit more care needs to be taken. However, valve cores are easily replaceable with standard tools. In comparison, on Schrader valves this requires a proprietary tool. Presta valves may come with a lockring that secures the valve body against the rim. This can make them a little easier to inflate. The dust cap is not essential to seal it, but helps keep the valve clean.
Dunlop/Woods valveThe only other type of valve you may come across is a Dunlop (also known as Woods) valve. This has a similar base diameter to a Schrader valve, but can be inflated with the same pump fitting as a Presta valve. You’re pretty unlikely to encounter one, and we’ve only really mentioned it for the sake of completeness.
A tubeless valve can be difficult to distinguish from a regular Presta valve. Oli Woodman / Immediate Media
Valves for tubeless setups are attached directly to the rim, rather than being part of an inner tube. More often than not they are Presta-type, though Schrader ones do exist. PART 2 : https://cyclingplus.my/how-to/how-to-pump-up-a-bike-tyre-everything-you-need-to-know-about-pumps-valves-pressure-and-0