ABOUT THE SRAM XX DH TRANSMISSION DRIVETRAIN
The XX DH Transmission drivetrain is based around SRAM’s T-Type drivetrain system, with the unique T-Type Flattop chain and reliance on their Full-Mount (UDH) frame mounting interface. This wireless downhill drivetrain features 7 gears and uses SRAM’s AXS wireless system to do without the gear cable.
SRAM studied the gate starts performed by World Cup Downhill mountain bike racers. Comparing the new XX DH Transmission with a previous-generation drivetrain, they found that in the first 15 metres of a downhill race run, the shifting-under-load capabilities of XX DH allowed the rider to gain 2.7kph (6.5%) extra speed, or save 1/20th of a second over this 15m acceleration effort out of the gate.
XX DH TRANSMISSION DERAILLEUR
The new XX DH Transmission Derailleur claims to be the strongest DH derailleur available, and there are multiple design elements that contribute. The Full-Mount design avoids the use of a derailleur hanger, instead bolting robustly into the frame. This boosts strength and stiffness, increases durability against impact damage, and provides more precision when shifting gears.
There’s a DH-specific inline cage featuring improved bracing angle for increased strength, and a shorter length for more ground clearance. This cage threads into the main derailleur body and has the same Type 4 damper as found in the other T-Type mechs. Due to the shorter cage length, this same Type 4 damper applies a higher chain tension force to the chain, keeping things in check.
The XX DH derailleur uses the SRAM AXS system to make wireless shifts in combination with an AXS pod shifter on the handlebar. The AXS shifting is said to offer improved shifting precision, and the SRAM AXS app allows riders to connect to apply updates and tune the system to their preferences.
The T-Type shifting uses a derailleur and cassette that work together, with cassette mapping allowing for the chain to remain constantly engaged to ensure uninterrupted power transfer when shifting. SRAM even says the shifting performs better under load, and while the noises may produce mild concern, the reliable shifting time after time confirms this fact.
SRAM makes the XX DH Transmission derailleur fully serviceable, with replaceable skid plates, outer parallelogram link, and a rebuildable cage.
Pricing comes in at $700 / €765 / £680 for the XX Downhill T-Type AXS 7-speed derailleur, with the battery not included (rrp $59 / €63 / £56). It tips the scales at 426g.
XX DH CRANKS
The SRAM XX DH Transmission crankset takes cues from their XO alloy crank, but has its durability dialled up to handle the rigors of downhill mountain biking. Even with this durability, SRAM claims a best-in-class weight for the XX DH Crankset, at 701g. The arms are given machined faces in key wear areas to prolong their fresh looks and fit in with the aesthetic of SRAM’s other top-level products.
SRAM made the XX DH Transmission crankset available in lengths from 165mm down to 150mm. The DUB spindle standard is used, with widths of DH for a 56.5mm chainline on either 157mm or 148mm rear ends, and Wide for a 55mm chainline on 148mm hub. Depending on the option selected, a XX DH T-Type chainring is available in 32T to 36T sizes, with DUB DH spindles coming with a more robust chainring, designed to resist folding when impacted.
Retail price comes in at $450 / €490 / £440.
XX DH TRANSMISSION CASSETTE
The new XX DH Transmission cassette brings the X-Sync tooth profile used on T-Type drivetrains to a 7-Speed DH-specific close ratio cassette. This delivers what SRAM claims to be their best shifting and most robust DH cassette to date, with excellent shifting capabilities under load.
SRAM offers two XX DH Transmission cassette variants to fit either standard XD or the newly developed XD SLIM standard. XD SLIM uses the 148mm hub standard, but its shorter cassette body allows the hub flanges to be wider, giving symmetrical and wider spoke bracing for a stronger rear wheel.
The 10-24T gear range is typical for a DH bike, and the 150g (XD fitment) and 144g (XD SLIM fitment) weight figures are impressive. The price comes in at $500 / €545 / £485.
THE COMPLETE SRAM XX DH TRANSMISSION DRIVETRAIN
Totaling up the weights of the components of the SRAM XX DH Transmission Drivetrain, you get a system weight of 1641g / 3.6lbs (including an AXS battery). The total retail price of the system is a handsome $2084 / €2253 / £2011.
THE DIRT
THE SETUP AND OPTIMIZATION PROCESS | I didn’t have to go through the setup process as the XX DH drivetrain was already fitted to my Mondraker Summum test bike as part of the SRAM MY27 launch camp. However, if my time installing AXS and cable-operated T-Type drivetrains is anything to go by, then it should have been a fairly simple process. SRAM’s documentation of the Prepare, Hang, Tighten process is excellent, and should let most home mechanics get the system dialed in with relative ease.
As for optimization, the components themselves required no attention throughout testing so far. However, I was able to optimize my own riding as a result of the system, which I’ll discuss later in the ride impressions.
HOW DID THE SRAM XX DH TRANSMISSION PERFORM? | The SRAM XX DH Transmission drivetrain blended into the background in use, for all the right reasons. When paying particular attention to the gearing, I ascertained that the shifting was flawless underload. There are times when as a bike tester, you do things that are outside of what you would consider normal or even acceptable bike riding, such as making a double gear shift and applying maximum power through the pedals just to discern how the system will react. In the case of the new SRAM DH drivetrain, doing so highlighted their shifting-under-load claims to run true, though the speed of these shifts is not as fast as your typical Shimano drivetrain. Even so, being able to maintain 100% power through the pedals during a shift far outweighs being in the perfect gear at any given millisecond, in my eyes.
I was impressed by how quietly the bike ran, especially given it was a non-idler equipped long travel machine. Admittedly, it was prepared and maintained by a World Cup mechanic, so a dialed bike should come with little surprise. But even so, a mechanic can’t magically prevent a chain from flailing, so the derailleur can take some of the credit here. I didn’t manage to hit the derailleur on trails where my pedals regularly found themselves in danger either, and it was nice to have the peace of mind that it would likely hold up should I manage to catch it or have a rock flick up.
NEW RIDING POSSIBILITIES | By the end of testing, I found myself using the XX DH drivetrain somewhat like a gearbox. I began to make shifts midway through a rock garden or in mid air, trusting that the chain would slot into place when I next laid on the gas. That’s a first for a non-ebike or gearbox drivetrain. When I was hammering the pedals, I never held back on shifting exactly when I wanted to, and I didn’t suffer a single problematic mis-shift. There were some loud, crunching gear changes for sure, but they never caused a skip or failed to move cogs as instructed.
The Wolf’s First Impression
SRAM’s XX DH 7spd AXS drivetrain simply worked, which is as much as you can ask from a drivetrain being hammered in a bike park for a few days. Add in the shift-under-load capabilities and the lack of gear cable, and there’s nothing on the market I’d rather fit to a downhill or park bike right now. Sadly though, the high price tag is going to prevent many riders from buying the SRAM XX DH Transmission drivetrain – it really ain’t cheap. 
Price: $2084 / €2253 / £2011 Complete System)
Website: SRAM.com
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ABOUT THE WOLF
Robert’s habitat is the Tweed Valley, Scotland, which is renowned for its root-littered enduro mountain bike trails. Robert has been developing his bike handling skills for the last 16 years. Since he was a pup, he’s been riding everything from BMX through to enduro and downhill bikes. Combining a playful style with occasional speed-focused aggression, he favors supportive bikes, and does his best to push them hard.
Rank: European Tech Editor
Size: 6’2” / 189cm | 220lbs / 100kg
Social: @robert_johnston
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