You’ll spend about half your race time completing the bike leg of a triathlon, so being fast will help your overall race ambitions. But, a fast energy-draining ride will slow your running. Therefore, being efficient on the bike is equally important, since this will preserve energy for the run.
If you’re properly set-up on your bike (i.e. the bike’s geometry works for you and you’re in the most comfortable aerodynamic position your flexibility and body strength will allow) a good set of wheels can shave up to 15% off your bike time.
But, choosing a set of wheels can be daunting and difficult even for the most experienced athletes. There are many manufacturers, agents and retailers whom will want you to buy their products. So, you need to make an informed choice. And, to do so you should know what to look for, what current developments are shaping the future and what’s going to work for you.
Generally, wheels comprise the following elements:
· Rims
· Hubs
· Brakes
· Tyres
Rims
Fact: In a non-drafting cycle race that requires a solo effort and where speed is a priority, the deeper your rims are the faster you will go.
A deep section rim typically has a profile of least 50mm. For the front a profile depth greater than 80mm is not advisable, since it will be near impossible to control. While you can go as deep as a disc for the rear. How deep you go (both front and rear) depends on a combination of your ability, strength and weight and of course the weather conditions.
Deep section rims are fast in two important ways:
1. A smooth aerofoil shape passes through the air more cleanly than a box section. The leading edge, which is usually the tyre, splits the air, while behind the tyre the deep rim controls the airflow by helping the air come back together again as soon, and, as smoothly as possible.
2. Deep rims “sail” in cross winds by creating forward thrust due to differences in air pressure between the up-wind and down-wind sides of the rim, much like a sailing boat sails against the wind by trimming its sails in relation to the wind and the direction in which the boat travels.
Deep section rims can have negative drag at high yaw angles thus propelling you (very slightly) forward.
And, all the “faster” factors mentioned above means that momentum is more easily maintained with a deeper rim. Once you have accelerated to a higher speed it’s easier to maintain that speed without having to stay hard on the pedals. In other words, you will require less power to maintain a given speed, or, you will go faster for a given power output.
Wind tunnel and velodrome conditions shaped the early developments in deep rims. The results were narrow rims, which were fast in the test conditions, but very unstable in cross winds. Subsequent developments revealed that a wider rim critically enables greater control of the airflow, since the airflow remains attached to the surface. Controlling the airflow and allowing the air to come back together again as soon as possible after leaving the surface of the rim are critical to the stability of the rim in cross winds.
While research and technological advancements will produce rims that are ever more stable, therefore easier to ride and consequently faster, you will still need to develop the necessary skills that are required to control deep rims.
Developing these skills takes practice. So, you should buy a set of deep rims that are robust enough to be ridden every day, including race day. A good set of deep rims can take an incredible amount of abuse and only risk being damaged if you crash. Riding with your deep rims every day will not only allow you to develop the necessary skills that are required to control deep rims but will also create confidence that your equipment will not break down before you reach T2 on race day.
Be aware that if you’re using tyres that need an inner tube make sure the valves are long enough to protrude through the deep rim so that you can inflate the tyre. The simplest solution is to buy tubes with a standard-length valve that have a removable valve core. Simply remove the core, add the appropriate length extension and put the core back in.
Hubs
Fact: The quality of a hub is determined by the precision in the manufacturing process. If the hub is not machined to precise tolerances the components will not align properly.
While the hub is a very important component of the wheel, all it really does is connect the axle with the spokes and the rim. The rear hub has a drive mechanism, but apart from providing a ratcheting mechanism, does little more.
A good quality factory-built hub will have the bearing seats and axles and even the outside shell shape of the hub turned on lathes that are well maintained and have very precise tolerances. Hubs manufactured with such precision are fundamentally better than those that are manufactured with inferior machinery, regardless of design.
Most hubs are fitted with radial load cartridge bearings, which are small and light. Bearing quality is important. But, it’s near impossible to improve the performance of a cartridge bearing based on ball or race quality. However, good quality radial load cartridge bearings are inexpensive, easy to service and easy to replace.
Cartridge bearings have seals that contact the outer and inner race, thus providing a seal that keeps dirt out and grease in, but also offers a small amount of resistance, which you can feel in a finger spin test.
Ceramic bearings mostly lower the contact of the seal (or eliminate it altogether) and use lighter lubricants, thereby making them spin better in a finger spin test. So, you could get comparable performance if you change the seals and lubricant of a standard good quality bearing.
Simply servicing the bearings regularly or replacing if necessary is all you need to do in order to keep your wheels running smoothly. Make sure your bike shop has the proper tools to align the bearings, otherwise you will feel a rough bearing and the bearing will also wear out quicker.
Brakes
Fact: Rim brakes will still be around for a while, but in the future most, if not all triathlon bikes will be equipped with disc brakes.
Why? Besides being (currently) slightly heavier than rim brakes and a little less aerodynamic, there are no disadvantages.
Since disc brakes were first introduced on road bikes there have been countless debates and “field tests” on the performance differences between the two systems. And, depending on the type of test or the theme of the debate, either system could be declared better.
However, without question disc brakes are superior in wet conditions. If you’ve ever ridden with full carbon rims in the rain you will know that the initial pull on a rim brake does not scrub-off any speed and even after you’ve cleared most of the water from the braking surface on the rim, it still takes some time to slow down.
Wet conditions though have little impact on disc brakes. And, as long as your tyres maintain grip with the road surface, you could one-finger brake from high speed. Furthermore, if the disc brake system is hydraulically controlled it will have better modulation. This means you can access the full range of braking power across the full travel of the lever. More stopping power for the same input and faster more predictable pad retraction when releasing the brakes means you have more ability to control your speed.
Add to this the element that triathlon bikes are notoriously bad at changing direction which can make them difficult to ride on technical descents, and, the introduction of disc brakes adds a significant element of safety.
As with rim brakes, there are currently two types of systems for disc brakes:
1. Cable or
2. Hydraulic
Cable systems have the disadvantage of friction and hydraulic systems have better modulation. Hydraulic systems are sealed and consequently dirt cannot get into the moving parts, which makes them almost maintenance free. Hydraulic systems are easy to set-up and adjust (with the correct tools) whereas cables need to be cut precisely and need tweaking as they stretch. Hydraulic systems are however usually more expensive than cable systems.
And, there are also two types of systems for attaching the wheels to the frame:
1. Quick release drop-out or
2. Through axle
A through axle system consists of a pin that must be threaded through the holes in the frame and fork tips to secure the wheels. There are no drop-out slots, so the through axle must be removed completely to release the wheel. Because a through axle pins the forks together it synchronises compression and reduces uneven loading. This helps since a disc brake naturally creates uneven forces on the forks. A drop-out also allows more flexing in the axle, which allows the rotor to shift and thus contact the brake pads, which causes the brake to drag.
Disc brakes also allow frame designers greater freedom, since the rear brake doesn’t need to be hidden behind the bottom bracket and the front brake doesn’t need to be hidden behind a fairing, thus allowing better airflow between the forks and the wheel.
Tyres
Fact: A tubeless tyre with sealant can run at lower pressure and is less prone to punctures. And, it can also run faster and with better grip.
There are three types of tyres:
1. Tubular
2. Clincher
3. Tubeless
Until now, road cyclists have had a choice of two options, tubular or clincher. For triathletes the simplicity of clinchers has made this the most popular choice. And, over the past few years new materials and wider rims have given rise to lighter and stronger clincher tyres with better shaped profiles that closely rival tubulars.
Mountain bikers though have been using tubeless tyres for some time, mainly because tubeless tyres can run at lower pressures without the risk of a pinch flat and a liquid sealant in the casing quickly fills small punctures. The casing however is usually thicker and heavier in order to meet the demands of off-road conditions.
A tubeless tyre is essentially a clincher, except the tyre and rim seal together. This requires a tubeless specific tyre, rim valve and rim tape. And, they require more maintenance and patience, owing to the difficulty of working with the very stiff bead and the need to replace the sealant every few months.
Nonetheless, a shift to tubeless tyres will probably run in step with the shift to disc brakes. The critical challenge for manufactures is to develop a tyre that is light (less than 300g) and strong enough to withstand high pressure inflation (over 8 bars) with a thin bead that hermetically seals with the rim.
A tubeless tyre is faster and safer than a superlight competition tyre. They eliminate the friction between tyre and tube, which is a chief contributor to rolling resistance. And, the danger of a blowout is significantly reduced, since they will never suffer a sudden loss of air pressure that could be triggered by a burst tube or valve tear off.
