The mountain bike gearbox is actually an absurdity. Filigree gear wheels, packed close together and with too few teeth by mechanical engineering standards, are subjected to murderous chain forces. And without any protection from the harsh biking environment. Mud, clay, sand, dust - everything that gets under the cleats also gets onto the chain; the dirt is almost magically attracted to the lubricant, without which no chain runs smoothly. Wherever metal meets metal and dirt grinds in between, material is removed. Even the hardest steel, not to mention the much softer aluminium, erodes between the pins and plates of the unsealed chains and on the flanks of the sprockets and plates. Only by replacing worn components in good time, especially the chain, can the drive system remain reliable (see box "Smart replacement").
Wear follows a simple logic: the higher the forces and the smaller the contact surfaces, the higher the wear. If more sprockets have to fit into the same installation space, it stands to reason that the contact surfaces inevitably become smaller and the wear pressure increases. Does this mean that eleven-speed drivetrains are only for high earners who don't care about the cost per kilometre when cycling?
Tooth loss stopped
Sram counters this and promises a four times longer service life than before for its XX1 triple chain. The reason for this is said to be a special coating and hardening. Shimano is also advertising a new, friction-reducing coating for the XTR chain. Marketing magic or technical progress? To test the wear under controlled conditions, we subjected three 1x11 drivetrains to a rigorous test on the BIKE chain test bench: Sram XX1, Sram X1 and Shimano XTR were subjected to 45 hours of rough forces, sand and water.
The result is overwhelmingly positive. The Sram-XX1 chain is actually the best link chain that the German-Americans have built to date, despite the further reduction in width. Both link wear and roller wear are significantly lower than with the ten-speed chains. The higher material quality is effective and compensates for the narrower design. The cheaper X1 chain also has significantly harder rollers than the ten-speed chains from Sram. In terms of link wear, which is decisive for the service life of the chain, it is at a good, medium level. However, Shimano's eleven-speed XTR chain shows slightly greater link wear than the extremely well-tested ten-speed XTR (BIKE 5/11). So Shimano loses some chain strength, while Sram catches up.
Sram has also improved its chainrings. While the aluminium chainrings were driven to the point of partial tooth failure by nine-speed and ten-speed groupsets in the last test, they showed clear signs of wear in the current test run, but were still intact at the end of the test. Depending on the skew, however, practical experience has shown that wear can increase further. Large-large causes the teeth to melt laterally and worsens the guiding qualities of the X-Sync blades.
More steel, please!
Shimano uses a hybrid blade with an aluminium carrier and high titanium teeth for the XTR. This ingenious design increases the weight by a meagre 30 grams compared to an aluminium blade, but significantly improves the wear behaviour. It confirms once again that aluminium is only the third choice as a gear material. Steel would be an even more wear-resistant and significantly cheaper gear material than titanium. But it is also a few grams heavier. Which is why it is not used for the noble groups.
Wolftooth Components from the USA manufactures stainless steel blades for the Sram cranks with direct mount (only with 24 teeth, 99 dollars). This part should have a significantly longer service life than the original blades. This is because the smaller the front blade, the greater the chain forces with the same pedalling power. So if you want to make your 29er bike with 1x11 mountain-going and wear-resistant, the hard 24-tooth stainless steel ring is an interesting tuning option.
The wear and tear on the Sram Elffach cassettes is exemplary. The XX1 relies on the tried-and-tested X-Dome technology, in which the entire sprocket set is milled from a solid block of steel, apart from the aluminium retaining ring. An insane, seemingly wasteful process, but with impressive results. The milled work of art is super light and exceptionally durable. But the price is correspondingly high. A list price of 434 euros for a wear part is hefty. And even the cheapest prices on the web are only a little under 300 euros. If you ride the XX1, you should always change your chain very early and not spend too much time on sprockets with less than 18 teeth, as there is a risk of premature wear. The X1 package, which is riveted except for the three smallest sprockets and also has an aluminium rear sprocket, proved to be just as stable in the test, but is still very expensive at a list price of €321. Even the XTR package with six titanium sprockets, which are mounted in pairs on spiders, is cheaper. The small Shimano sprockets are not as wear-resistant as the Sram cogs, but can be replaced individually.
Thin and strong
The laboratory test in BIKE 10/2015 shows that the use of an eleven-speed system does not necessarily mean more wear. This is in line with our experience with road bikes, where single-speed has long been the standard and also sets the benchmark in terms of durability. How long the components last is primarily determined by the materials and hardening processes used. Therefore, the Elffach technology will probably not increase the kilometre costs for normal bikers if the technology of the high-end groupsets is passed on to the low-cost drives.
Conclusion Dipl.-Ing. Robert Kühnen, Test Engineer
"The manufacturers have done a good job and designed the eleven-speed components to be quite robust. The durability is on a par with the ten-speed drivetrains. However, steel would be desirable as a gear material for the front of the single blade. This would significantly extend the replacement intervals."
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SWITCH SMART
Wear and tear cannot be avoided when mountain biking. If you want to prevent high costs, you should replace the chain in good time. This is also recommended in terms of safety.
Chains and sprockets are wearing parts. During operation, the chain inevitably elongates and changes its so-called pitch: what was initially an even 12.7 millimetre distance from pin to pin becomes a sequence of long-short-long. This leaves marks in the sprockets and leads to the chain slipping on small sprockets in the long term. To avoid this effect, it is advisable to replace the chains at the latest when the joints are worn by 0.075 mm/joint. The easiest way to measure the elongation is to use swivelling chain gauges such as the Rohloff Caliber. If you have missed the replacement time, a new chain will no longer work with the worn sprockets. You can then continue to run the lengthened chain, which often works well for quite a while. However, this reduces operational safety. The chain is less well guided and can suddenly fail. The entire gearbox then has to be replaced. It is therefore better to check the chain regularly and replace it in good time, especially with high-quality drivetrains. The cassettes will then last for several chain lifetimes.
LUBRICATE BETTER
How quickly a drive wears out depends on the external conditions. And on the right care. You should pay attention to this.
Chain wear depends heavily on environmental conditions, maintenance and preferred gears. Riding in mud with gear reductions is the worst for the chain. Regular mechanical cleaning of the chain and sprockets increases the service life. A combination lubrication system has proved effective: first drizzle viscous oil onto the joint gaps and leave to work overnight. Then rub the chain dry with a cotton cloth and seal with hard wax (car care). The wax seals the gap and does not attract dirt. Prepared in this way, the chain will survive three Transalp stages without relubrication.
You can read this article or the entire BIKE 10/2015 issue in the BIKE app (iTunes and Google Play) or buy the issue in the DK shop reorder:
