SRAM Red AXS XPLR in the test: With a 13-speed sprocket and UDH rear derailleur, the new gravel group is causing a sensation. We tried out the core components after lightning-fast assembly and compiled everything you need to know about the new Red.
Last summer, the US component manufacturer presented a new road bike group in the top segment. The 2024 SRAM Red AXS surprised with a new lever shape that replaced the eight-year-old predecessor, and there were also various detailed improvements. Visually, SRAM opted for continuity; technically, sticking to the 2×12 shifting principle ensured complete compatibility with older SRAM parts.
Then came the gravel bike version of the new SRAM Red, and it really had it all as the first electronic groupset with 13 sprockets on the rear wheel. With a direct mount rear derailleur, this set also represents a departure from the usual drop bar technology. So what does the SRAM Red AXS XPLR offer the gravel community? Is it worth upgrading to 1×13, and what does it cost?
SRAM Red AXS XPLR: only with UDH rear derailleur
The biggest difference to previous gravel groups is of course the rear derailleur, which is tailored to the UDH standard known from mountain bikes. SRAM calls its electronic rear derailleurs “Transmission”, which are mounted directly on the frame and no longer attached to a derailleur hanger. This is missing from the UDH frame – you can see how it works on Velomotion here The important basic information is as follows: A UDH rear derailleur can not be mounted on a conventional frame; of course it works the other way round - a classic rear derailleur also fits on a modern UDH frame. More and more manufacturers are converting their gravel bikes to the new standard, and the new SRAM Red AXS 13-speed can only be mounted on these models.
SRAM's MTB groups are still 12-speed, and their electronic UDH rear derailleurs have already been used on gravel bikes in the past. All AXS rear derailleurs are compatible with all AXS shift levers. Until now, however, UDH on gravel bikes was always called "Eagle" - that's what the Americans call their long rear derailleurs designed for MTB cassettes (up to 52 teeth). The new Red rear derailleur is therefore the first direct-mount model that is tailored to gravel cassettes with a smaller gear range.
SRAM Red AXS XPLR 13-speed cassette: closer gradation and larger overall circumference
These so-called XPLR cassettes previously ended with a 44-tooth pinion; the SRAM Red now has a 46-tooth sprocket for the first time. SRAM has used the 13th pinion to achieve a narrower gear ratio and a larger gear range at the same time - the following comparison of different cassettes from the company shows what this looks like in detail.
SRAM Red XPLR 10-46 13f. 10-11-12-13-15-17-19-21-24-28-32-38-46
SRAM XPLR 10-44- 12f. 10-11-13-15-17-19-21-24-28-32-38-44
SRAM Force 10-36 12f. 10-11-12-13-15-17-19-21-24-28-32-36
SRAM Apex HG 11-44 12f. 11-12-13-15-17-19-21-24-28-32-38-44
The 13-speed cassette is the first XPLR sprocket to offer four sprockets in one-step increments. It has a 12-tooth sprocket and two more teeth in the lightest gear ahead of the 10-speed 44-12 cassette. In addition, the new cassette has eleven sprockets that are just as closely spaced as the popular 10-36 road bike cassette that is installed on many gravel bikes with a 2x12 drive from SRAM, usually combined with a 46/33 crankset. The two-speed transmission used to have two significantly longer overdrive gears, but the new 1x13 gear system has an easier mountain gear. And, as mentioned, with just as fine a step. So you could say that the 13-speed group is the first one-by transmission that no longer has any disadvantages compared to two-speed drives for gravel bikes - apart from the very long overdrive gears that you don't necessarily need for gravel bikes. In addition, if you ride the 1×13 with a 42 chainring, you get a slightly longer fast gear and still have the same mountain gear as the double system.

"Mix & match" with existing components
It is therefore clear that the 13th pinion does offer advantages - but now the big question is: can the new drive be retrofitted at all? And if so, at what cost?
You can - and the thing officially costs 1.460 euros. The only condition is that you have a gravel bike with a UDH derailleur hanger and some SRAM AXS group. This is where compatibility comes into play: SRAM has not changed the pinion spacing on the 13-speed cassette, but simply added another sprocket. This sits on the inside, where the spoke slope provides enough space. The 13-speed cassette fits on the well-known XDR freehub body, and the installation width of the rear wheel remains the same. In addition, the XNUMX-speed chains that SRAM has been using for years remain. "Mix & match", in other words, which makes switching to the new transmission pretty easy.
Large rear derailleur without adjustment screws
Before assembly, let's take a look at the new SRAM Red rear derailleur: It looks quite large, which is something we already know from the manufacturer's MTB derailleurs, and it also has no adjustment screws. This is also one of the advantages of the UDH principle: the position of the cassette or rear derailleur is precisely defined, as there are no longer any differently shaped derailleur hangers. The distance between the upper derailleur pulley and the cassette also no longer needs to be adjusted (for which SRAM used to have a special alignment gauge). When assembling, you only need to pull the shift arm back a little until the chain no longer sags, and then screw the rear derailleur tight - now it is in the perfect position.
Greater stability, greater precision
But why a direct mount rear derailleur? The advantage of the solid construction is, on the one hand, the greater rigidity of the system, which ensures more precise gear shifting. On the other hand, the rear derailleur is less susceptible to damage - it moves inwards when hit hard. If it gets caught somewhere, the forces introduced are not transferred to the frame, but to the rear wheel's thru axle, which is intended to protect the frame from damage. And since there is no longer a derailleur hanger, it cannot bend, which would in turn impair the function of the gearshift.
The installation of the UDH rear derailleur is unusual at first, but quite simple – you can find detailed video instructions hereOnce mounted, there is no need for any adjustment - as mentioned, there are no stop screws. However, you can use the electronic fine adjustment via the AXS shift levers, which move the rear derailleur inwards or outwards in 0,25 mm increments.

Lightning-fast assembly on the Cube gravel bike
To try out the new SRAM parts, we took apart a Cube gravel bike that was already equipped with a 10-speed UDH gear system (albeit in the Eagle version with a 52-13 cassette). All we had to do was change the rear derailleur and mount a Zipp wheelset with the 30-speed cassette; connecting the Red rear derailleur to the Cube's levers took maybe XNUMX seconds. To complete the look, we also installed the super-light SRAM Red crankset on the bike. SRAM had also lent us the new power meter, which now consists of two parts - the chainring is screwed on and can be replaced when it is worn or when you need a different number of teeth.
Two and a half hours of pure gear shifting pleasure followed, because the direct mount shifter really works phenomenally. The chain moves quickly and precisely from one pinion to the next; compared to a conventional electronic derailleur, you can feel the greater precision of the entire system. On asphalt, the narrow gradation of the cassette in the fast range pays off; on the mountain, 40-46 is a really easy gear, which can also be used to manage very steep passages. The greater slant of the chain on the largest pinion is not noticeable - this is where the great lateral flexibility of SRAM's "flattop" chain comes into its own.
The elegant integration of the battery is striking in the rear derailleur, which is no different from that of older SRAM derailleurs. The delicate "Magic Wheel" shift pulleys consist of two parts, the plastic gearing and an aluminum carrier, which are not firmly connected to one another - if the "spokes" of the shift pulley are blocked by a branch or something similar, the gearing can continue to rotate and the shift arm is not damaged. The rear derailleur itself can be disassembled so that individual components can be replaced if they are defective.
SRAM Red AXS XPLR: Big, but not that heavy
The UDH rear derailleur may look big, but it is not that heavy: at a good 400 grams, it weighs around 70 grams more than a Force XPLR rear derailleur, but you also have to add 25 grams for the derailleur hanger - so in the end the 13-speed derailleur only weighs around 50 grams more. The 13-speed cassette, on the other hand, weighs 290 grams, almost 90 grams less than a 12-speed SRAM XPLR XG-1271 with 10-44 teeth. So if you only convert the rear derailleur and cassette, you save around 40 grams. Switching from the Force to the Red crankset saves a good 150 grams at an additional cost of a good 200 euros (237 or 450 euros). The Red crank plus power meter costs a whopping 1.235 euros.
Based on the retail prices of the sprocket, cassette and crankset (without power meter), the upgrade to 13-speed made our Cube Nuroad C:62 SLX just 300 euros more expensive, especially since Cube uses high-priced components from the SRAM transmission. For a gravel bike equipped with SRAM Force AXS, the surcharge for the rear derailleur and cassette would of course be higher. The upgrade kit consisting of a 13-speed cassette and Red rear derailleur is available from major online retailers for around 1.250 euros; plus a set of SRAM Rival levers (approx. 400 euros), a chain (30 euros), brake discs (70 euros) and a Rival crankset (130 euros), and the electronic high-end gear group is ready for under 1.900 euros. The complete Red group, including the corresponding new shift handles and brake calipers and discs, officially costs around 4.000 euros – without a power meter.
Alternatively, you can of course hope that SRAM will do the same as with the Eagle Transmission for MTB and offer cheaper versions of the 13-speed transmission in the future. Anyone who is currently planning to build their own gravel bike – let’s say based on the excellent “Specialized Crux DSW“-frame that is already equipped with UDH mount – you should definitely consider the variant described above. A direct-mount rear derailleur and 13-speed cassette on a gravel bike definitely make sense.
Of course, the new SRAM Red XPLR is not without its disadvantages. There are currently no other cassettes - for example with other gear ratios - that are compatible with the 13-speed sprocket. If you ride multiple wheel sets on your gravel bike, e.g. with different tires, you have to buy a second sprocket or convert yours from one rear wheel to the other. This is much easier with the current XNUMX-speed gravel groups from the US manufacturer: the electronic groups and the mechanical Apex also shift closely spaced road bike sprockets, and operation with Shimano cassettes also works.
Only Classified offers a compatible 13-speed cassette with 10-36 teeth, but this is only compatible with the manufacturer's gear hubs. This means you can at least turn a 1x13 gravel bike into a 2x13 all-road bike - an interesting but expensive option.