(Test from BIKE 8/2016) 50 sharp teeth rotate on the huge sprocket in the rear wheel of our test bike, while the smallest cog of the Sram XX1 Eagle manages with ten. This spread (500 % on the cassette) is a real novelty. The developers have extended the cassette to twelve gears and want to make multiple chainrings on the crank superfluous. The Eagle completely dispenses with shifters, derailleurs and shift cables: 1x12 is the approach.
The abbreviation Di2 indicates that Shimano uses electronic shifting. The electrified version of the top XTR groupset still has two (or three if required) chainrings, but the space for the shifter on the left-hand side of the handlebars can also remain empty*. The shifting is clever: the rider selects whether they want to shift up or down using the shift lever on the right-hand side. One click and the chain moves one sprocket further; if the skew of the chain becomes too great, the system also changes the chainring accordingly to set the correct gear ratio. Several gears can also be shifted. If small gears are required, the derailleur automatically changes gear, signalled by a short beep. The Japanese system does not require any shift cables, but does require power cables and a battery. The range of the tested system: 26 and 36 teeth on the crank and an eleven-speed cassette with 11-40 teeth, i.e. 2x11.
The decisive role in the comparison of single versus double is played by the gradation of the gears and the range of the gear ratio. The question is: Do amateur athletes also feel comfortable with the set-up of both systems, or are they reserved for racers? Ergo: Are there enough gears available for a fine gradation? Is the lowest gear sufficient for steep ramps, and does the highest gear deliver enough speed?
The handling of the XTR Di2 is as simple as it is smooth. The shift clicks of the lever are clearly defined. The lower, slightly longer shift lever shifts to the higher sprockets, while the small upper button throws the chain down to the heavier gears (reverse mapping is programmable). The eleven gears on the cassette with 11 to 40 teeth engage quickly, hardly any pressure needs to be taken off the pedal. It is easy to change the chainring under load - although it is somewhat rougher than on the cassette. As known from mechanical derailleurs, a short release accelerates the change of the front chainring and prevents grinding. A small display on the stem provides information about the gear engaged.
The gears on the XX1 Eagle engage as crisply as usual. Upwards (towards the large sprockets), up to six gears are possible with one press of the long lever. Even under load, the long cage shifts the chain over the sprockets with definition and precision.
The downshift requires a separate click for each sprocket. So if a crest is followed by a steep descent, you quickly have to shift several times. The Di2 can shift several gears: If you leave your finger on the lever, the rear derailleur and front derailleur rattle through all gears to the end stop.
For speed passages, both gears deliver almost identical values: at a cadence of 80 revolutions per minute, the Sram achieves 34.0 kilometres per hour and the Shimano 34.8 kilometres per hour - with 27.5-inch wheels. In the lightest gear, the cruising speed at 80 crank revolutions is 6.8 (XX1) and 6.9 km/h (Di2). These values are on a par with classic gear ratios with triple chainrings and are also perfectly adequate for amateur athletes.
Theoretically, the XTR only has 22 gear combinations available, but the automated shifting (Synchro-Shift) means that there is a maximum of 16, as the system always switches to the large chainring after reaching the fifth sprocket. If you subtract the double gears, which produce a very similar ratio due to the two chainrings, you are left with 13 well-graded gears. The Eagle offers twelve.
In terms of the bare facts, both drives are on a similar level. However, the preference of the testers after the system comparison speaks a different language: the simplicity is convincing. Why fit lots of electronics to your bike when a good mechanical groupset delivers very similar effects - and manages with significantly fewer components?
This view is shared by Timo Wölk, who works as a developer for various manufacturers in the bike industry. Wölk sees rosy times ahead for bike designers with the single groupset. "Everything becomes more variable when the front derailleur is eliminated: We gain a lot of installation space. We can use this for more tyre clearance, shorter rear triangles, strength and weight optimisation." Sceptics of the single systems always bring up the unsprung masses of the giant cassettes. On closer inspection, however, this turns out to be a waste of time: there are only 30 grams between the two high-tech cassettes from Sram and Shimano.
Overall, the Di2 loses a lot of ground in terms of weight: the drive unit weighs 1747 grams. This is an excellent value if you consider that it also contains a display, a battery with control electronics, etc. In comparison, you still save a whopping 266 grams with the XX1 Eagle, as it manages with significantly fewer components.
As expected, the reduced number of components in the Sram Eagle also brings a price advantage over Shimano's Di2 - but both groupsets are still expensive: you have to hand over 1521 euros to your trusted bike dealer for the XX1 Eagle. The Di2 costs 2749. Anyone reading these figures quickly realises that for normal bikers, the systems are currently hardly an option for the equivalent value of full complete bikes. The same applies to the maintenance costs: the chains are priced at 92 euros (XX1) and 65 euros (XTR). Things get serious when the cassette is worn out: €300 is due for the 11-speed XTR sprockets, the XX1 Eagle cassette even costs €458!
...
IT'S THE TRANSLATION THAT COUNTS
Is the low number of gears sufficient to provide the rider with the full range? The diagram shows: Both gears are extremely variable.
This is how the diagram reads:
At a value of 100 %, the rear wheel rotates just as fast as the crank. A lower value means that the rear wheel turns slower than the crank. You need these gears to ride uphill. Large values indicate a fast gear ratio.
Spreading and gradation:
The values for the lowest gear are almost identical: 64 % for the XX1 and 65 % for the XTR. This means that even normally trained bikers can climb steep ramps. For comparison: A triple crank with a 22 t chainring and 36 t sprocket delivers 61 %.
The gear gradation of both systems is also at a similar level. In the highest gear, the XTR is 7% higher than the XX1. Compared to a 44t chainring with an 11t sprocket (400%), the biggest deficits are in high-speed passages.
Weight and price:
The weight of both systems is at an excellent level. The XTR requires significantly more components. As a result, its weight is 266 grams higher. The price points still offer plenty of room for improvement. You have to put 2749 euros on the table for the Di2 from this test.
...
DETAILS
Electronic control or pure mechanics. The circuits are expensive high-tech works of art.
AND SO IT GOES ON:
SRAM X01 Eagle: No sooner had the XX1 Eagle technology carrier been presented than the second groupset with the new technology followed. The X01 Eagle also manages a 10-50 sprocket set and costs €1,301 in a comparable configuration.
Shimano XT Di2: The electronic XT shifting system has the same features as the large
sister. The only restriction: the gear lever only allows one click, whereas the XTR has two. The price is 1564 euros.
CONCLUSION Dipl.-Ing. Stephan Ottmar, BIKE tester:
Light, simple and functional: Due to the numerous advantages, we predict a great future for single drives on mountain bikes. The products are still expensive, and the exorbitant spare parts prices in particular are a deterrent. However, the potential to transfer the technology to more affordable drivetrains is there. The newly introduced X01 Eagle is already 220 euros cheaper than the XX1 at 1301 euros. Even if Shimano also electrifies the next most affordable groupset with the XT Di2, these drivetrains are likely to remain a niche in the future. The gain in performance is too small to justify the expensive price, the complex assembly and the additional weight.
OPINIONS:
...
