Gates belt: Everything you need to know and a comparison with the chain
Hardly any bike with gears today can do without a timing belt. "The e-bike boom of the last few years has given the Gates belt another huge boost," says Frank Schneider from the European Gates distributor Universal Transmissions in Mühltal, Thuringia. The sight of sharply contoured, black belt teeth in shiny silver pulleys is also the epitome of modern bicycle technology for many people. Initially, only high-quality touring and frequent traveller bikes were equipped with the more durable but expensive belt drive, but today Gates belt systems are used on bicycles and e-bikes of all types and in all price segments. Competitor Conti fell by the wayside in 2018 following quality problems and a recall (keyword: IKEA bike).
Low maintenance
"The most compelling argument is actually always the low maintenance," says Schneider. First-time buyers of e-bikes in particular, who are not already familiar with bicycle technology and maintenance, attach extreme importance to having a bike that works under all circumstances at all times. In addition to a flat tyre, they are particularly worried about the bike chain, which is known to require regular maintenance and care. However, it is not the case that the Gates belt drive is maintenance-free. "That's why we explicitly use the term 'low-maintenance' to avoid misunderstandings from the outset," clarifies Schneider. Because even the durable plastic belt with its elongation-resistant carbon tensile fibres does not last forever.
Variants for every need
The Gates system is offered in three versions of interest to us: CDX (Carbon Drive Extreme), CDC (Carbon Drive Commuter) and CDN (Carbon Drive Network). The simple ST (Sidetrack) version works with simple flanges on the belt pulleys and is only intended for occasional cyclists.
Load capacity Service life of Gates belts
Of the three versions relevant for intensive wheel use, CDX is the one with the highest load capacity, durability and price. According to Gates' own measurements, it offers three times the service life of a comparable chain drive. CDC with two and a half times the chain life and CDN with one and a half times the chain life follow.
However, this information should only be used as a guide and should not be taken literally.
Material and design of the belt drive
All Gates belts are constructed in the same way and have the centring groove called the centre track. However, they differ in material: CDX uses polyurethane, CDC and CDN ethylene elastomer as belt material. The front pulleys are made of hardened aluminium (for regular bicycle cranks) or steel (Pinion and mid-engine compatible bikes), while the rear pulleys are made of steel or stainless steel. For e-bikes, Gates also approves the CDX system for the most powerful mid-motors up to 90 Newton metres, while the CDC variant is only approved for low-assist drives with torques up to 50 Nm. CDN is not approved for e-bikes and is only recommended for less intensive use on bicycles.
Short digression: Basic knowledge about Gates belts
- The ribs make it easier for the Gates belt to nestle around the pulleys.
- Eight carbon tensile fibres prevent the belt length from ever changing.
- The PU core of the belt carries the teeth.
- A nylon fabric layer ensures abrasion resistance of the teeth.
- The centre track groove centres the belt.
- The separating layer separates material and mould during production. It has no function during driving and slowly wears away.
In terms of price, the versions are difficult to categorise: they are only sold directly to bicycle manufacturers. A price classification can only be derived from the sales prices of bikes with Gates belts. In most cases, there is no comparable bike with a chain instead of a belt for a direct comparison. But that's the point: the Gates belt has almost completely replaced the chain in gears. Spare parts such as pulleys, sprockets and belts are available in the Universal Transmissions webshop, in some cases in regular online shops and, of course, in specialist shops.
Wear on the Gates belt
The belt drive works perfectly as long as the teeth of the belt engage positively in the spaces between the pulleys without interference. Then the power from the crank is optimally transmitted to the rear wheel with only minimal loss. However, never cleaning and maintaining the system just because the transmission medium is made of plastic instead of metal is too short-sighted.
Dirt particles always sneak in between the Gates belt and pulleys and dig into the surfaces of the parts due to the pressure during power transmission. However, as a relatively soft surface (belt) meets a very hard one (pulleys), unlike with a chain drive, the belt loses substance first. The fact that the blue or black inner layer wears away is not yet wear. It only serves as a separating layer to the mould during the manufacture of the belt blank. After the first 100 kilometres, its abrasion slowly stops. However, once thousands of kilometres have been accumulated under dirty conditions, you can usually see a clear change in the tooth profile of the belt: It becomes more pointed, slimmer or irregular where the webs of the pulleys have dug in.
Price and replacement of a belt
Longitudinal cracks may appear in the belt body, individual teeth may break off or fall out. Then it's time to replace the belt. You should then also take a close look at the belt pulleys: Often, but not always, the rear sprocket pulley, where fewer teeth have to bear the load than on the larger front pulley, also has signs of wear. The webs show edges where they, like the belt teeth, have been exposed to the dirt-abrasive paste. Depending on the load, you can expect a worn set of sprockets approximately every two to three Gates belt lives. With significantly smaller rear axle sprockets (Rohloff, Alfine), these wear out correspondingly earlier. However, the degree of wear always depends heavily on the circumstances, such as how much force is applied to the pedals, how heavy the bike and rider are, how often the drive is cleaned and whether the routes are mostly asphalt or off-road.
Depending on the number of teeth and Gates belt variant, you can roughly expect costs of between 100 and 180 euros (only the belt is replaced) or 250 to 350 euros (belt and both pulleys are due). In either case, you will have to buy replacement parts with the same number of teeth and of the same or higher quality. The advantage of the belt is that, even at maximum wear, it only loses substance on its inner side and thus continues to engage precisely in the spaces between the pulleys. Elongated chain links do not do this. They no longer fit congruently into the spaces between the teeth on the sprocket and chainring, run up and slowly grind the teeth into metal dust.
Does a Gates belt absorb power?
Yes, the Gates belt absorbs more of the pedalling force than a chain. The joints of a chain rotate around the sprockets with less friction than the stiff belt. The belt is forced into the curve with every bend, the material is slightly squeezed each time and then expands again. This internal friction generates heat and is comparable to the rolling of a tyre as it unwinds. In addition, a belt runs under a defined pre-tension for safety reasons. Plausible measurements by Universal Transmissions show an efficiency of around 99 per cent for the chain and between 98 and 98.5 per cent for the belt, with a relatively low loss of around one to two per cent to the chain, depending on the load range - if the belt and chain are new and well-maintained.
If both are heavily (100 %) or very heavily (200 %) worn, the belt is always more in the lead and the chain deteriorates considerably. This can be seen on Universal Transmissions' technically comprehensive YouTube channel, which is highly recommended for all belt users. In addition, there is a multitude of other measurement approaches by independent inquisitive people, some with deviating results, some of which were later recognised as incorrect. However, it is difficult to objectively evaluate the different approaches. The efficiency of a belt, for example, also depends heavily on the degree of pre-tensioning. And it varies depending on the wattage of the force applied.
In addition, a bicycle drive applies the power in a pulsating manner and not linearly like a test bench motor. This is why opinions are still divided on the actual efficiency of the belt drive. The undeniable loss of power is reflected in a longer journey time or lower speed over a given distance, but always remains a mystery. This is because the cyclist's form on the day, road surface, gradient or wind conditions, and even whether a hub dynamo is in use, have a major impact.
Conclusion on the Gates belt
Physically, it is a fact that the low maintenance of the belt system is paid for with slightly higher power input. However, everyone involved agrees that the efficiency losses are more of an academic nature and can be measured and calculated, but are not noticeable when driving. If you want to delve deeper into the arguments, Georg Schmeisser and Prof Dr Hubert Hinzen from the University of Trier's Faculty of Engineering are committed protagonists in this discussion. But there are countless other panellists. The length and technical depth of the debate also show how much is still unexplored when it comes to the seemingly so simple bicycle and cycling. And they show how close the gap between chain and belt apparently is - for this reason alone, it has earned its place in the annals of bicycle technology. Even initially stubborn belt refuseniks in the industry now offer belt-compatible frames. In practice, the constantly optimised belt has impressively shown the chain its teeth.
