The Presta valve (also French valve (FV) or Sclaverand valve) is a type of tire valve commonly found on high pressure bicycle inner tubes and is commonly used on tubeless setups. It consists of an outer valve stem and an inner valve body. A lock nut to secure the stem at the wheel rim and a valve cap may also be present.
The Sclaverand valve was invented by Frenchman Etienne Sclaverand and is often referred to as the French valve. Today it is also known as Presta valve. [1] [2] Presta or presto stands in the Romance languages for "fast, hurry, immediately". [3]
The outer valve stem is manufactured in various lengths to cater for the different depths of the wheel or rim. It is recommended the valve stem is to be at least 10 mm longer than the rim is deep to allow adequate room for the bicycle pump to be attached. It has a narrower diameter of 6 mm (0.24 in), compared to Dunlop and Schrader valves, measuring 8 mm (0.31 in). The weakest point of a bicycle rim is usually the hole for the valve stem. The smaller hole for a Presta valve makes it possible to have extremely narrow wheels while maintaining sufficient strength in the wheel. [4] [ better source needed ]
The air pressure in an inflated tire holds the inner valve body shut. A small screw and captive nut on the top of the valve body permits the valve to be screwed shut and ensures that it remains tightly closed.
The nut must be unscrewed to permit airflow in either direction. The screw remains captive on the valve body even when unscrewed fully; it is tightened again after the tire is inflated and the pump removed. The valve cap protects the valve body, keeps dirt and mud out of the mechanism, and also prevents the valve from damaging the tube when it is rolled for storage, but is not necessary to prevent pressure loss.
The holes in rims sized for Presta valves can be enlarged to accommodate the wider Schrader valves, which can structurally weaken the rim. Conversely, when a Presta valve is fitted into the larger Schrader rim hole, grommets or reducers are sometimes used to take up the extra space.
The standard Presta valve has an external thread. An adapter can be fitted onto this external thread to permit the Presta valve to be connected to a pump with a Schrader chuck. The same adapter, because of a coincidence of thread sizes, may be able to convert a Schrader pump into one that can connect to flexible adapters of either kind. [4]
Unlike Schrader valves, not all Presta valves have removable cores.
Presta valves with removable cores may be used with a tube or tubeless setup to add sealant through the valve. Sealant may also be added by pouring it directly into the tire. [5]
Valve extenders can be used to lengthen shorter Presta valves to accommodate deeper and thicker rims, such as those on aerodynamic race wheels. There are two variants of valve extenders depending on whether the Presta core is removable. [6]
The valve threads for Presta valves follow the ISO 4570 standard. [7] The external threads at the tip of both "threaded" and "unthreaded" Presta valves are 5V2 (#12-24TPI), which measures out to 5.2×1.058 mm, [8] the same thread size as the tip of a Dunlop valve. The external threads on the main body of "threaded" Presta valves are 6V1, which measures 6×0.80 mm. [8]
A tire valve goes through a hole in the rim, and the hole slightly weakens the rim. Presta valves are thinner than Schrader valves, so can fit through a smaller hole. For bicycle rims which are narrow and lightweight (thus highly stressed), a smaller hole makes the rim and wheel stronger. For most other uses, the difference in strength is too small to matter.
Presta valves can use a push-on air chuck with a simple diaphragm seal. This can be fast on/off and also leads to a lightweight pump chuck. Schrader valves often use either screw-on chucks, which are slower; clamp-on chucks, which are heavier; or push-and-hold chucks, which must be held to prevent leaking, and which are commonly used with air compressors but rarely used with manual pumps. For bicycle racing, a Presta pump's "fast and light" can be an advantage. A push-on diaphragm Presta chuck tends to push the valve stem in to the tire cavity, which slows down getting a good seal. It is thus common to secure the stem with a nut against the rim. However, the nut must be removed to change the tube, and removing the nut takes time, which is a disadvantage for racing. A diaphragm-seal chuck works on a stem without a stem nut, but it takes more skill - a disadvantage for casual use.
Presta valves use air pressure to hold the valve closed, then use a small nut to ensure the valve stays sealed in use. Loosening the nut takes time, which is a disadvantage for racing. Leaving the nut loose still allows the valve to seal, but may make it easier to have accidental (or malicious) deflation. Schrader valves use a spring to close, so Schrader chucks use a "pin" to open the valve while the chuck is attached. This avoids the Presta's nut, but leads to use of slower screw-on or heavier clamp-on Schrader chucks.
Presta valves are mainly used on bicycles, and are rarely used on cheaper bicycles. Presta pumps are thus less common. If you are carrying a pump, this is rarely an issue. For more casual use, it can be an advantage to not carry a pump - one less thing to lose, malfunction, or have stolen. However, there may not be a Presta pump available when you need it. There are adapters to fit a Schrader pump on a Presta valve, but loss/theft of the adapter can still be an issue. Adapters can leak, a disadvantage compared to a Schrader chuck on a Schrader valve.
At very high speed - approximately 150 kph - Schrader valves can open under centrifugal force, leading to a flat tire. Racing cars often use valve caps with a seal and with the cap strong enough to withstand a tire's air pressure. A Presta valve has a nut holding the valve closed, but this is not an advantage in practice, as ordinary bicycles never go fast enough to open a Schrader valve. Further, at least some motor-paced speed record bicycles have used Schrader valves. (The actual speed of Schrader opening depends on many factors; 150 kph is only a very rough guide. The important observation is a Presta valve's nut is not an advantage in actual use, because ordinary bicycles do not go fast enough for it to matter.)
A mountain bike (MTB) or mountain bicycle is a bicycle designed for off-road cycling. Mountain bikes share some similarities with other bicycles, but incorporate features designed to enhance durability and performance in rough terrain, which often makes them heavier, more complex and less efficient on smooth surfaces. These typically include a suspension fork, large knobby tires, more durable wheels, more powerful brakes, straight, wide handlebars to improve balance and comfort over rough terrain, and wide-ratio gearing optimized for topography, application and a frame with a suspension mechanism for the rear wheel. Rear suspension is ubiquitous in heavier-duty bikes and now common even in lighter bikes. Dropper seat posts can be installed to allow the rider to quickly adjust the seat height.
A bicycle wheel is a wheel, most commonly a wire wheel, designed for a bicycle. A pair is often called a wheelset, especially in the context of ready built "off the shelf" performance-oriented wheels.
A bicycle pump is a type of positive-displacement air pump specifically designed for inflating bicycle tires. It has a connection or adapter for use with one or both of the two most common types of valves used on bicycles, Schrader or Presta. A third type of valve called the Dunlop valve exists, but tubes with these valves can be filled using a Presta pump.
A valve stem is a self-contained valve that opens to admit gas to a chamber, and is then automatically closed and kept sealed by the pressure in the chamber, or a spring, or both, to prevent the gas from escaping.
A gate valve, also known as a sluice valve, is a valve that opens by lifting a barrier (gate) out of the path of the fluid. Gate valves require very little space along the pipe axis and hardly restrict the flow of fluid when the gate is fully opened. The gate faces can be parallel but are most commonly wedge-shaped.
The Schrader valve is a type of pneumatic tire valve used on virtually every motor vehicle in the world today. The Schrader company, for which it was named, was founded in 1844 by August Schrader. The original Schrader valve design was invented in 1891, and patented in the United States in 1893.
August Schrader (1807–1894) was a German-American inventor and mechanic. He is known for inventing the Schrader valve.
A collet is a segmented sleeve, band or collar. One of the two radial surfaces of a collet is usually tapered and the other is cylindrical. The term collet commonly refers to a type of chuck that uses collets to hold either a workpiece or a tool, but collets have other mechanical applications.
A globe valve, different from ball valve, is a type of valve used for regulating flow in a pipeline, consisting of a movable plug or disc element and a stationary ring seat in a generally spherical body.
The term bicycle tools usually refers to specialty tools only used on bicycles, as opposed to general purpose mechanical tools such as spanners and hex wrenches. Various bicycle tools have evolved over the years into specialized tools for working on a bicycle. Modern bicycle shops will stock a large number of tools for working on different bicycle parts. This work can be performed by a trained bicycle mechanic, or for simple tasks, by the bicycle owner.
A flat tire is a deflated pneumatic tire, which can cause the rim of the wheel to ride on the tire tread or the ground potentially resulting in loss of control of the vehicle or irreparable damage to the tire. The most common cause of a flat tire is the puncturing of the tire by a sharp object, such as a nail or pin, letting the air escape. Depending on the size of the blowout, the tire may deflate slowly or rapidly.
A fitting or adapter is used in pipe systems to connect sections of pipe or tube, adapt to different sizes or shapes, and for other purposes such as regulating fluid flow. These fittings are used in plumbing to manipulate the conveyance of fluids such as water for potatory, irrigational, sanitary, and refrigerative purposes, gas, petroleum, liquid waste, or any other liquid or gaseous substances required in domestic or commercial environments, within a system of pipes or tubes, connected by various methods, as dictated by the material of which these are made, the material being conveyed, and the particular environmental context in which they will be used, such as soldering, mortaring, caulking, plastic welding, welding, friction fittings, threaded fittings, and compression fittings.
A tubeless tire is a pneumatic tire that does not require a separate inner tube.
Inspection and maintenance of tires is about inspecting for wear and damage on tires so that adjustments or measures can be made to take better care of the tires so that they last longer, or to detect or predict if repairs or replacement of the tires becomes necessary. Tire maintenance for motor vehicles is based on several factors. The chief reason for tire replacement is friction from moving contact with road surfaces, causing the tread on the outer perimeter of tires to eventually wear away. When the tread depth becomes too shallow, like for example below 3.2 mm, the tire is worn out and should be replaced. The same rims can usually be used throughout the lifetime of the car. Other problems encountered in tire maintenance include:
The Dunlop valve, is a type of pneumatic valve stem in use—mostly on inner tubes of bicycles—in many countries, including Japan, Korea, India, Pakistan, Sri Lanka, most European countries, and a number of developing countries. The Dunlop valve has a wider base than a Presta valve, similar enough in size to a Schrader valve to use identically drilled valve holes in rims, but it can be inflated with a Presta valve adapter. The inner mechanism of the valve can be replaced easily, without the need for special tools.
A bicycle tire is a tire that fits on the wheel of a bicycle or similar vehicle. These tires may also be used on tricycles, wheelchairs, and handcycles, frequently for racing. Bicycle tires provide an important source of suspension, generate the lateral forces necessary for balancing and turning, and generate the longitudinal forces necessary for propulsion and braking. Although the use of a pneumatic tire greatly reduces rolling resistance compared to the use of a rigid wheel or solid tire, the tires are still typically the second largest source, after wind resistance, of power consumption on a level road. The modern detachable pneumatic bicycle tire contributed to the popularity and eventual dominance of the safety bicycle.
A tubular tyre, referred to as a tub in Britain, a sew-up in the US, a single in Australia, or just a tubular is a bicycle tyre that is stitched closed around the inner tube to form a torus. The combination is then glued onto a specially designed rim, referred to as a "sprint rim" in Britain, and just a "tubular rim" in the US, of a bicycle wheel.
The following outline is provided as an overview of and topical guide to tires:
