Table of Contents
- A new feature and experience
- The tire and the rim
- Mounting and inflating
- Presta Valve
- Tire Pressure
A new feature and experience
This started with my discovering the difficulties of dismounting tubeless ready tires from my gravel bike in the fall of 2019 and the spring of 2020. Changing a tire is not supposed to be a job requiring shop time. Tires, in principle, can be repaired and replaced by a user.
The pneumatic bicycle tire was one of the technologies that made the safety bicycle successful. It evolved by innovations in wheels, wheel rims, tires and inner tubes into the clincher used on most bikes, including the utility bikes common in 20th century. The tire casing is a laminate of fabric and rubber. The tread is hardened rubber laminated onto the casing.
The Bicycle Technical Information (“BTI” ie Sheldon Brown) tires page discusses the kinds of tires, including the tubular tire used in racing. The dominant technology uses clincher tires and inner tubes. The BTI page on flat tires summarizes. This illustration (from a Wikipedia page) shows a tire, tire bead, inner tube, bead channel and hook, in a cross-section view. The diagrams and pictures at Bike Gremlin, Bike Touring News and Cycling Tips (below) also illustrate.
- rim tape, in a central well or valley (in a tubeless ready wheel);
- rim braking surface (on a wheel for a bike with rim brakes);
- bead, laminated to tire casing, engaged by the bead hook in the bead channel;
- inner tube;
Pneumatic tires became the dominant technology for automobiles and motorcycles. The tire industry developed tubeless tires and rims for motorized vehicles and for lightweight carts and appliances.
Tubeless bicycle tires were developed for mountain bikes and gradually acccepted for use on other bikes. Tubeless tires are supposed to recover from minor punctures during a ride and repaired later. Tubeless tires are used at lower pressure than the same tire with an inner tube, which is desireable in many kinds of riding. Tubeless ready rims and wheels have become, arguably, the standard equipment for new bikes in many price and quality classes. A tubeless ready tire is a tubeless tire without the sealants and the tubeless valve. It is basically a clincher, and requires an inner tube. Some tubeless ready wheels have rim tape, but not all of them. The rim tape may extend over the shelves of the bead channel. Many riders carry an inner tube to repair a tubeless tire in the field.
Cycling Tips, an online publication, published a guide to tubeless tires, An Endless FAQ, in 2019 and updated it in 2021 [updated October 2021].
The tire and the rim
The normal process for detaching (unmounting) a clincher tire and replacing an inner tube is shown in this Park Tool video. A clincher normally disengages from the rim easily when the tire is deflated. After disengaging the bead, it may be necessary to use tire levers to get the bead off the rim. Hydraulic, pneumatic and manual bead breaker devices are available and basically necessary for agricultural, industrial, truck, automobile and motorcycle tires, but such devices are not used in bike shops and almost never available for a roadside repair.
It is harder to unmount a tubeless tire than an ordinary clincher. Tubeless tires fit tightly. Friction between the tire casing over the bead, and the bead channel in the wheel rim is a major factor. The bead channel may be machined to wrap around and hook over the bead. If the tire was mounted with sealant for tubeless use, the sealant may a factor. When the tire has been deflated, the bead has to be pushed off the shelf into the valley in the middle of the rim. It is necessary to unhook the bead and push it into that valley. This takes some force, but can be done without tools or extreme measures. It may be necessary to work around the rim and push in at several places and find the best place to gets the bead out of the channel and continue around the rim and get it out of the channel before pushing it into the valley. It may be necessary to do this on each side. I found videos of methods for extreme instances on YouTube:
- The Brighter Cyclist, using tongue and groove (aka pump) pliers, April 2017
- Bike Teacher, using a vise, July 2017;
- Double Tap, February 2020;
- The Biking Viking, another vise, August 2020.
Some sources advise riders to practise the skills of dismounting a tire and installing or changing a tire in order to reduce time lost on a ride. This skill involves tactile feedback and muscles that may not have been worked that intensively for some time. It is worth learning.
Mounting and inflating
It is easy to press one bead into the rim. The user may want to align a marking on the sidewalls with the valve hole at this stage. The inner tube can be pressed into the tire when one side of the tire has been pressed into the wheel. The inner tube should be empty or nearly empty. The valve stem should be pressed through the hole in rim, and the inner tube positioned with the stem perfectly perpendicular to the rim.
Getting the remaining (second) bead into the rim can be done by hand if the beads are kept down in the rim channel. It is better to run fingers along the sidewall of the side that is already on the rim to make sure it is in the well. The remaining side can be pressed into the rim, starting some distance from the valve. It may be best to start opposite the valve. About half of the remaining side will fit easily, but the rest will also yield. It can be worked in short sections. It may be necessary to pinch both walls to make sure the first side is still in the well. It may be necessary to hold the bead down in one place with one hand while working the bead that is still outside along the rim with the other hand. Eventually, the section still outside the rim will be short enough that it can be be pulled into the rim. It can be done by hand. Using tire levers to pry the tire over the rim presents the risk of catching the inner tube and creating a pinch flat.
It is advisable to work the fingers of one or both hands along the sidewalls to find any places the tube may protruding outside the edge of the sidewall or caught, and press the sidewalls back to release the inner tube. The sidewall can be rubbed and pulled up into the bead channel. A tubeless rider will follow a similiar process, but will need to take extra steps to get a preliminary seal.
If the valve is a threaded Presta valve – which is common on modern bikes, the captive nut (which threads on the thin rod that fits inside the stem) should be tightened down. This locks the valve core in the closed or sealed position. The BTI glossary entry on the Presta valve and several articles by Jobst Brandt are informative. The presta valve has an internal stem that seals the valve, which is locked by a tiny nut threaded on a thin brass rod. A Presta valve does not have an internal spring. The stem rod can be easily bent or damaged! It is worth a little preventative care, and some caution in use. The external cap that threads onto the exterior of the stem does not have retain air, but provides some protection against impacts on the stem cap rod.
The stem cap rod is brass, and bends. One risk it that a pump hose, a pump or a pressure gauge can bend the stem cap rod while the device is being attached to or removed from the valve stem. The threads cut on the outside of a Presta stem can in theory be used to screw on a pump hose but that is rare – many chucks friction fit over the end of a stem or are locked with a lever.
If the tube seems to be leaking from the valve core, and core is a removable threaded core, it is worth tightening the core with a tool (that can grasp the part of the core above the end of the valve stem).
When both beads appear to be in place, start pumping. The beads of a tubeless tire often will audibly pop into place. The valve stem may have a jam nut that threads onto the outside of the stem to hold the stem in the wheel rim. See above – this nut should be tightened down.
The pressure marked on a tire is a consumer protection warning – a fraction of pressure that will blow the tire with an inner tube off the rim. It is not a recommendation for performance. High pressure was believed to lower rolling resistance, but that theory or belief has been contradicted. The operating pressure is normally much lower than the marked pressure. The maximum pressure for 700c x 38 with an inner tube is 75 psi. I ran the Panaracer Gravelking SK at 60 psi; I got less rolling resistance in the low 50’s and mid to high 40s (psi). For a 38-40 mm tire, with an inner tube, the pressure will be in the 3 to 3.2 bar range or lower. The recommended pressure for tubeless use is even lower. Fatter tires run at lower pressures. The appropriate pressure depends on several factors. The modern thinking is stated in this Cycling Weekly article. There are some good online calculators; a couple are noted in the article. I have used the Silca calculator. The full “pro” version is free, although at this time it requires registration by entering an email address.