Rolling Resistance In Triathlon Tyres
Triathletes understand how much of a hindrance wind resistance can be in terms of speed and energy expenditure, as this is something they are often reminded of. You can tell the difference when you move from the aero position or enter and exit the slipstream of another cyclist.
Although it is significantly easier to notice variations in something large, it can be much more challenging to detect the difference between one wheel or frame and another if the change is only in aerodynamic drag.
A wind tunnel is a great tool for gathering the info necessary to reach conclusions. Sometimes you may even be able to get an idea by using a stopwatch or power meter, however, it is highly unlikely you’ll be able to perceive a tangible difference.
Rolling resistance is a bit like that. You can sense the variance in friction when going on a knobby tyre as opposed to a slick tyre, or when pushing on a tyre that has been inflated to 1 bar (14 psi) versus 6 bar (87 psi).
Nevertheless, it will be impossible to detect any sort of variation in the rolling resistance when you increase the tyre pressure by half a bar (7 psi) or adjust the tyre width by 2mm.
It is also necessary to change between tubular, tubeless clincher and tube-type clincher models, as well as when switching between leading brands of tyres intended for racing. Nevertheless, as in the wind tunnel, a suitably engineered laboratory study can show the variation, and it can be considerable.
If you are using a power meter while cycling, you understand that a change in power output of just 10 watts is considerable. This could amount to between three to five per cent of your average energy output while biking during an Ironman competition, which would make a big difference in your completion time.
It could indicate a chance to be in Kona or simply observe from the comfort of one’s home in October.
However, there is frequently a disparity between the amount of power needed to push two correctly pumped race tyres of one kind, label, or style compared to another on the flat pavement; the difference grows even larger on bumpy roads.
Hysteresis and tread compounds
When examined on a laboratory’s even surface, a tyre’s rate of rolling resistance decreases with higher inflation pressure.
A graph of tyre pressure and rolling resistance would demonstrate the relationship between the two. The graph would begin with high rolling resistance and low tyre pressure on the far left, ultimately progressing towards the right with an increase in tire pressure and a decrease in rolling resistance.
Historically, some triathletes have been convinced of the accuracy of this downward trend in the results, to the point that they choose tyres as skinny as 19mm with air pumped up to 180 psi and higher (in this particular circumstance, they use tubular).
If the tyre is extremely stiff and unyielding, like a bare rim rolling on glass, it won’t be able to gain traction. For the tyre to have sufficient traction, it must be composed of soft and adhesive material (such as a rubber mix).
When rubber is compressed and then allowed to recover, it will become warm. It is possible to observe the effects of letting go of a solid rubber object, such as a lacrosse ball or a Superball.
The balls are very bounceable on pavement and the height of each hop is slightly reduced in comparison to the one previous. The effect of the delay in motion that occurs is referred to as “hysteresis” and can’t be avoided in a tyre; as it moves forward, some of its energy is always dissipated as heat because of hysteresis.
A softer tread that increases hysteresis loss is needed to gain more traction, whereas harder tread materials lead to less rolling resistance. But not all tread compounds are created equally.
Certain rubbers are capable of providing more traction with lesser lowering of the rolling resistance compared to others. The exact combination of additives and natural rubber which go into the formulation of a tyre’s tread compound is jealously guarded by the manufacturers. Additionally, the method and timing of their sequence are also closely monitored.
Fat tyres can roll fast
For the tyre to manage any uneven surfaces on the road, it must have a certain level of elasticity. The rougher the surface is, the more flexibility is needed.
Tyres have air inside their outer covering that provides cushioning, which increases when either the air pressure is low or the weight on the tyre is high.
Similar to a rubber tread, some energy is lost as heat when a section of the tire casing is rolled against the ground and then resumes its original shape when it moves away from the pavement.
If the air pressure and force of the load are the same for two tyres of different sizes, the area in which the tyres touch the road will stay the same, regardless of the size of the tyre.
A slim tyre will need to flex more significantly near the bottom to cover the same area as a wider tyre when it hits the road; the area of contact with the ground will be longer than the broad tyre’s width.
A casing that does not bend as much produces a lower hysteresis loss in the wide tyre.
Higher pressure can be slow
A bike with really tough tyres felt energized and zippy, gliding across the road surface – and, wow, those 19mm tubular filled above 180psi truly had a boost in energy! But that bouncing is also energy lost from propulsion.
If the tyres are overly stiff, the whole weight of the cycle and its rider will be noticeably raised by each small imperfection in the road.
Sucking in bumps in the frame of the bicycle uses energy from the cyclist that could be used to move the two-wheeler, causing the rider to wear out quickly. The energy that was originally propelling the bike and its rider in a forward direction is now solely being used to lift the bike and the rider vertically.
The key to travelling quickly using minimal energy when traversing bumpy terrain is to ensure the bicycle and rider remain stable and don’t bounce up and down while they move forward.
If the tyre’s air pressure is significantly low and the size of the tyre is great, it can soak up a shock so that the rim won’t rise at all.
The only portion of the tyre (and any inner tube present) that deflects rolling up the hill is a small amount of mass. The bike and rider have significantly less mass, which leads to a decrease in the energy that is dissipated.
When navigating uneven, bumpy terrain, the rider’s body absorbs the jolts, resulting in energy being lost in the damping process. A laboratory examination of rolling resistance can effectively recreate this energy loss.
Many triathletes have started to wear compression clothing, demonstrating a broad appreciation of how vibration can induce muscular exhaustion.
Tyre type and size are important
Jan-Niklas Jünger, who is the bicycle tyre product manager at Continental, states that the more material distorts, the greater the rolling resistance will be. A tyre with a large and/or lumpy profile or a tyre with a deep tread will create more friction on the ground compared to a 25mm road tyre, and an inner tube made of heavy-duty butyl rubber will add to the degree of drag.
When it comes to selecting between skinny tyres and broad tyres, the decision becomes more complicated.
The subject of tyre width has gained increasing attention among those in the road cycling sphere in recent years. 25mm tyres are now widely used in events, surpassing 23mm tyres, and some riders have even opted to go even larger.
When both tyres are pumped up to the same pressure level, they have the same contact surface, while the form of the patch which is touching the ground differs vastly. A tyre with a slim width has a long and slender area of contact, whereas a tyre with a wide width has a short and wide area of contact.
The extended flat area of a slim tyre causes the wheel to become less rounded as it rotates, thus generating more distortion.
In comparison, the area of contact with the ground is shorter with a wider tyre; thus, the tyre is curvier and moves faster.
You would probably fill up a wide tyre with less air than a skinny one. This will increase the size of the area in contact, resulting in more rolling resistance.
Nonetheless, Continental’s data indicates that when using a 25mm tyre, 94psi is adequate, yielding the same level of rolling resistance as a 23mm tyre for which 123psi is necessary. A 28mm tyre filled with air up to 80psi will experience the same amount of rolling resistance.
You need to get your tyre pressure right
If your tyres become misshapen, leading to greater rolling resistance, then you should fill them up with air as much as possible and wait for your Strava KOMs to come in, correct?
It’s never as easy as that, is it? Take a spin on the sleek ground of the velodrome and, sure, you can fill your tyres with up to 8-12 bar (116-174psi) pressure, but you need to take into account the track you’re biking on for other rides.
Jan emphasizes the importance of connecting with the ground when off-roading. He states that lowering the tyre pressure helps the driver to remain consistent with the terrain and improve speed.
You may decide to use a 32mm tubeless tyre inflated to 3 bar (44psi) for a Paris-Roubaix race but this does not usually apply to others.
Jan states that travelling on the street is very dissimilar, depending on the texture of the path you are heading towards. You must select the air pressure for your tyres based on the type of road surface.
Riders should begin to explore running their air pressure lower in a tyre meant for road use with no tube; a 25mm tyre should not have any more than 6 bar (87 psi). By looking at our data, we observe a point where the rolling resistance on extremely even surfaces no longer falls.
People can have fun with some good apps, and pressure transducers from Quarq and SKS.
Quarq SKS
The tyre carcass makes a difference
The basic frame of the tyre, which can be produced from a variety of materials, is essentially the framework of the tyre.
Jan explains that Continental has a polyamide material that’s used as the foundation of their tyres and the amount of threads per inch varies. He states that the higher the number of threads per inch, the lighter the tyre will be due to the reduction in the thickness of the material. You can get a low-cost mountain bike tyre with 27 threads per inch and a strong chassis material. We increase the TPI to a maximum of 200 and the fibre’s diameter decreases.
The material is usually folded three times in typical tire configurations, and there are multiple patents on how to fold the carcass, such as if there is a triple layer in the core or other strategies of folding.
As the width of the fibre reduces, the amount of rubber used to encase, secure, and separate the threads diminishes, letting the tyre become lighter due to the high thread-per-inch count. It is not always the case that a higher tyre pressure index will result in better rolling resistance. A tyre can only be quicker when the optimal combination of a high thread count per inch and a thin layer of suitable rubber material is utilized.
Manufacturers employ various rubber mixtures in the construction of the casing, depending on how the tyre will be used.
Jan states that when selecting tyres for downhill mountain bikes, you need to look for tyres with good damping, which would be different than those used for time trial tyres or GatorSkins, which are designed to be durable and tough.
A puncture breaker can affect rolling resistance
Many producers layer puncture breaker protection between the tyre body and the tread which can impact rolling resistance.
Jan emphasised that the kind of breaker you use can have a major impact, particularly when it comes to bicycle tyres. A puncture breaker can make the difference between an expensive bicycle tyre and a regular one.
An advantageous quality of our patented Vectran breaker is that it has no effect on the rolling resistance. However, using a basic puncture-resistant layer or a polyamide fabric will result in an increase in the general rolling resistance.
The Continental SuperSport Plus tyres are ideal for messengers, hardcore commuters and fixie riders due to their thick casing rubber which creates a higher level of sidewall durability. Additionally, the Plus breaker belt is a thick elastomer layer located beneath the tread that helps defend against punctures. The downside is that these tyres are not as rapid as others in the selection.
The GrandSport tyres boast a nylon NyTech breaker, whereas GatorSkins possess a PolyX breaker composed of a densely woven polyester fibre that should not reduce rolling resistance.
You can’t have it all when it comes to the tread
The rubber on a tyre, commonly referred to as the tread, has a huge impact on its overall performance and speed. This is understandable.
Jan explains that when attempting to improve one characteristic of a tyre tread, it is important to be aware of the other two characteristics, mileage, grip, and rolling resistance, as they are all linked.
If you choose the tyre that has the fastest rubber compound available, you can be certain that it will not provide reliable traction on slick or wet surfaces. If you wish to have a tyre that provides excellent grip on the road, be aware that it will take longer to accelerate and will wear down quickly, similar to a pencil eraser.
Companies devote a great deal of effort to designing rubber mixtures that help them to achieve the desired outcome for a particular purpose.
A winter training tyre needs a compound that emphasizes strength and grip in wet conditions, while a time-trial tyre should have a compound that reduces rolling resistance.
