Robert Mennen pinches the shoulder stud of a Magic Mary front tyre and twists it by twenty or thirty degrees. He concentrates and suddenly releases his grip: the rubber straightens out almost immediately - but only almost immediately. "This is the simplest test of all," he says. "The slower the cleat turns back, the more the rubber dampens." A very, very fine thermometer would register that the stud has become warmer due to the rotation and resetting. The mechanical energy from Robert's fingers has turned into heat.
If you take a step back from the tiny lug, you can see one of the basic dilemmas of tyre technology. The twisted lug is all about damping versus rolling resistance: the better damped and therefore more controlled the tyre behaves, the more driving force is converted into heat. This increases the rolling resistance. Or coarse studs that deform the ground: Great grip, but again that tiny, energy-sapping micro-heat ... What's fun on the downhill sucks the battery and muscles dry on the uphill.
And these are just two of the many optimisation problems in tyre design. Mennen, a former Cape Epic winner, is now Product Manager for mountain bike tyres at Schwalbe. His job is to balance the contradictions between the four goals of grip, damping, puncture protection and wear in such a way that every biker can find their personal favourite tyre for their favourite route in the Schwalbe range - resulting in a gigantic product variety of over 300 tyre models.
Apart from the tyre size and width, tyre developers of all brands vary three parameters in particular: Carcass structure, tread pattern and rubber compound. "I actually think that we offer all sensible variants of a model," says Mennen, "and yet sometimes people come along who want tyre model A with carcass B and compound C."
The development of a new tyre model costs a six-figure sum on the hardware side alone. Vulcanising moulds and machine parts are expensive, so nothing can go wrong. They have therefore set up a huge test laboratory at the Schwalbe headquarters in Bergisches Land. Robert Mennen names the individual pieces of equipment. They are test stands for tensile strength. They are test rigs for resistance to bounce, ozone resistance, wear when cornering, rolling resistance, puncture and puncture resistance, braking grip and so on. Photos are not allowed. But more exciting than the aquariums full of aluminium profiles, electric motors and displays is the knowledge that goes into the tests and results from them.
Mennen's colleague Lars Funke carries two solid aluminium wheels with racing bike tyres to a testing machine in the laboratory. The almost treadless racing bike tyres hold a secret: a new mountain bike rubber compound is about to undergo laboratory testing. "We first vulcanise the new compound onto racing tyres for the laboratory tests," explains Robert Mennen. "Because they have no tread, we can be sure that differences in grip, rolling resistance or wear can be explained by the rubber."
Tubeless was a real milestone. This simultaneously improved puncture resistance, rolling resistance and - thanks to the possible low pressure - grip. Since then, tyres have of course continued to develop. But rather in small steps. - Robert Mennen, Schwalbe
Over one hundred different ingredients go into a compound. Natural latex, synthetic latex, oils, colourants and fillers. And although rubber tyres have been vulcanised since 1839, development continues. The filler silica, for example, has only been in use for a good two decades. In the right dosage, it improves wet grip and at the same time reduces rolling resistance while minimising wear - three parameters that were much less compatible with the rubber formulations used until then. Even with the latest compound, there is an optimisation problem between the three objectives of grip, rolling resistance and wear. But at a higher level. A fourth requirement is the environmental aspect: tyres wear out when driving. They scatter fine dust and microplastics into the landscape. The German automobile club ADAC has determined in tests that a car leaves behind an average of 120 grams of abrasion per 1000 kilometres. In terms of sporty trail kilometres, this is probably no less for mountain bikes.
Schwalbe's sustainability team sees itself as a pioneer in the industry. The self-imposed goal is to "successively reduce the environmental impact by optimising the rubber compounds. We want to ensure that tyre wear is not harmful to the environment" - without compromising performance, of course, as Product Manager Mennen adds: "What use is a tyre that feels like you're riding in a bag of nuts?"
The compound is only responsible for part of the riding performance. Schwalbe, Continental and Maxxis all agree that the right rubber compound contributes around a third of the performance. Aaron Chamberlain, the responsible product manager at Maxxis in the USA, summarises the tasks of the components compactly: "The compound influences the grip, the casing determines puncture protection and rolling resistance, the tread design primarily affects handling and rolling resistance."
Track reading: What difference do the studs on a bicycle tyre really make?
Why do the treads look the way they do? The example of Schwalbe's enduro classic "Magic Mary" makes it clear what considerations go into the tyre profile. It is no coincidence that the competitors' enduro tyres resemble this design.
The fact that the studs are angular (and not oval) gives them a lot of edge length and therefore grip across the respective load direction. The diameter of the studs is related to their height. High lugs generate a lot of grip in soft ground, but they lead to a spongy ride, especially on firm ground, due to their bending. A large base area stabilises them. The disadvantage: Large lugs stiffen the tyre overall and thus increase rolling resistance. If they are made of a soft, grippy compound, their internal friction has the same effect. Dual compounds with a harder inner layer are a possible countermeasure.
The shoulder lugs are particularly striking. On the "Magic Mary", they are arranged at a slight angle; when used as a front tyre, they are arrow-shaped in the direction of travel when viewed from above. On contact with the ground, they then stand up in a V-shape. In this way, they are loaded in the longitudinal direction (which tends to be stiff) when the driver turns and brakes at the same time. If they were positioned the other way round, this force would bend them in the narrower transverse direction - an important argument in favour of directional mounting.
In this tyre segment, the centre lugs almost always appear in groups of two or three. They thus form a crossbar with high braking force without unnecessarily stiffening the carcass on the tread. More and smaller lugs tend to be found on cross-country tyres with less tread depth. The centre lugs are reinforced with small ramps at the front (in plan view) against the braking load, which should also reduce rolling resistance.
Small slots in the upper side of the lugs, known as grooves, are intended to make the first few millimetres of the tread more supple without greatly affecting the overall stiffness.
According to all those interviewed, the design of the tread is predominantly aimed at the best possible performance in the respective area of use. However, in order to aesthetically improve the (often technically sensible) combination of different tyres on the front and rear wheels, the manufacturers also pay attention to a consistent brand look in small details.
Special tyres for E-MTBs?
Special tyres for e-mountain bikes are hard to find in the range of the major suppliers. Schwalbe's "Eddy Current" model is an exception - and shows where the journey is heading: the tyre is wide and relatively heavy, but designed for robustness. Nevertheless, Product Manager Robert Mennen says: "We already have over 300 tyre models. And it doesn't make sense to launch another 'e-version' of these tyres. Above all, a tyre for E-MTBs needs a particularly puncture-resistant, robust casing. We have these in our range anyway." Maxxis and Continental do not offer performance-oriented off-road tyres in a special e-version either. Continental's Alexander Hänke sees similar differences to his Schwalbe colleague: "On the rear wheel of a muscle-powered bike, you don't have to worry much about uphill traction.
But this is now an issue. In order to bring the torque of the powerful E-MTBs to the ground, you can work on the profile and the width. According to our ride tests, however, the existing models in a large width are up to the task. So there is no need for a new tread design. The second point is the typically less agile track choice with a long, heavy bike. To avoid punctures and other damage, we therefore always recommend the next most robust carcass, for example an enduro carcass for a trail bike." In short: If the tyre is one class wider, more robust and has a coarser tread pattern than a similarly designed muscle chassis, it should work perfectly on the E-MTB.
Similar to the compound, the carcass, i.e. the load-bearing textile construction inside the tyre, has to stretch in different directions. Ideally, it would be as supple as a silk scarf, as puncture-resistant as a protective waistcoat and as robust as a fighting dog toy. No surprise: that's not possible. Many thin, close-lying threads (i.e. a high TPI value) are supple and reasonably puncture-proof, but not particularly cut-resistant or puncture-proof. They are suitable for muscle-driven cross-country bikes. For more safety, manufacturers add several layers or additional materials under the tread and in the area near the rim. Sharp stones, sharp thorns and overlooked edges then have less of a chance of bringing the rider down. However, if you overdo it with safety, such a carcass rolls as tough and bumpy as a layered liquorice snail. That's not much fun, even with the engine.
It is no coincidence that the major tyre manufacturers in the upper price segment offer at least three different robust carcasses. There are worlds of difference between "light, fast, sensitive" and "stiff but bulletproof" in terms of rolling resistance and handling behaviour. And this is the point in tyre development where the material meets reality beyond the laboratory doors. Once the basics have been perfected in the laboratory, a long and systematic practical phase begins. Maxxis man Aaron Chamberlain draws a line under this: "For things like material development and quality assurance, lab testing is useful. But beyond that, you don't learn much from a steel roller."
Tyre testing in practice: athletes, employees and ambitious amateurs with a feel for the material
The big brands also sponsor professional teams and individual riders out of an interest in knowledge. Hardly anyone has more practice and finer sensors than the cracks. Schwalbe also has access to a network of ambitious amateurs when it comes to checking a new development. "These are people who not only ride a lot, but are also very aware of what the material is doing," explains Product Manager Robert Mennen. "And even with tried-and-tested testers, riders from colleagues and teams, we try to gather their riding impressions as objectively as possible. This includes anonymising the test tyres, i.e. not specifying the model name, carcass or compound. We also make sure that there is no collusion among ourselves. Otherwise we can easily have an opinion leader and it's psychology that decides, not the driving experience." To be on the safe side, the testers are sometimes given the same tyre twice in the course of a test series without knowing it.
The Schwalbe-sponsored downhillers from the Commencal / Muc-Off team, including multiple overall World Cup winner Amaury Pierron, were not content with a role as test riders. They took up knives and pliers themselves to optimise the material. They chipped away at the profile of the standard "Big Betty" tyres until the riding behaviour came closer to what they wanted. They then used the results to initiate the development of the new "Tacky Chan" downhill model with the sponsor. Robert Mennen, an ex-pro himself and a rubber connoisseur, explains the result: "We changed the centre lugs and left more space between them and the shoulder lugs. We have reinforced these in turn. Now the tyre is lighter and generally more agile, but, as desired, also more snappy and precise on the edge. It needs to be ridden very actively. So it's not really a tyre for touring bikers."
It is a new tyre for a very specific niche. And there are almost as many of them as there are bikers. Heavy riders on root trails, light bikers on granite or limestone rocks, speed junkies in the urban forest: every requirement profile is special. And there is a suitable tyre for every one of them - or it is being created right now ...
Mature fish for beginners
Compound: The rubber compound or compounds of a tyre. This mixture of dozens of ingredients, from dyes and fillers to oils and different types of rubber, is tailored to the area of use of the tyre model and has a significant influence on grip, smooth running and wear.
Dual/Triple Compound: Dual compound refers to either a combination of harder, easier rolling rubber in the centre of the tread and a softer rubber in the side area of the tread, or a two-layer construction in which a harder bottom layer supports the lugs. A softer, grippier compound lies on top. Triple compound is a combination of the two dual compound variants.
Carcass: The textile, load-bearing basic construction of a tyre. It usually consists of several crossed layers of parallel threads (polyamide, rarely also cotton) and textile puncture protection layers.
Silica: "Pyrogenic silicon dioxide" or silica. As a filler, silica partially replaces other materials such as carbon black in high-quality tyres. At the same time, it is intended to increase the wet grip, smooth running and service life of the compound.
TPI/EPI: "Threads per inch" or "ends per inch". The number of threads indicates the fineness of the carcass - more and therefore finer threads are considered to be of higher quality. Be careful when making comparisons: some manufacturers (such as Schwalbe and Maxxis) specify the number of threads in a single ply, while others add up the carcasses, which are generally multi-ply.
Tubeless: Because real tubeless tyres would be too stiff and heavy on a bike, like on a car, bike tyres are only "Tubeless Easy" or "Tubeless Ready". They must be ridden with sealant. Only the sealant prevents the air from escaping through the flexible tyre sidewalls.
