Mechanical Transmission MTB drivetrain ditches batteries, shifts under load two gears at a time [Tested]

We all smelled this day coming like a steamy pie in the SRAM kitchen window. They gave us a taste of stand-on-your-derailleur glory with the release of their new T-Type battery bits not long ago, and the mechanical goods were sure to follow. Enter the new Eagle 90 Transmission mechanical group, employing the same stompable UDH frame connection as the robot version, with a lower price and no stinkin’ batteries.

The brand’s new servo-operated drivetrains supplanted their podium models of XX, XO, and GX for fancy race rigs, and from what I can tell these fresh mechanical versions slot in roughly where the GX and NX model lines once were. So GX drivetrain lovers have a choice of cables or lithium, and everyone else will join the charge to recharge — or not.

In this review

Installing the Eagle 90 Transmission drivetrain
Rebuildable and repairable
Pedal impressions on the trail
Eagle 90 Transmission specs, weights, and prices
Final thoughts
- Pros
- Cons

Apart from swapping the battery with a tiny steel cable, the Eagle 90 gruppo we tested is notably similar to its electric cousins. It uses the same chain and cassette tech to keep shifting crisp under load, the direct-mount derailleur is wicked simple to install and adjust, and the cranks come with nifty integrated bash guards that are hungry for a good stump smash. In short, it’s the same — but analog.

Installing the Eagle 90 Transmission drivetrain

Hanging these components on my Raaw Madonna was quick and intuitive. The most time-consuming elements were locating the proper chain length with SRAM’s AXS app, and swapping the seat-stay on my frame from its conventional hanger to one with a UDH dropout. The app provides bike-specific chain length, tells you which of the two settings the derailleur flip-chip should be in, and tells you which cog to shift to before tightening the derailleur in place. Yes, there is a two-position flip chip in the derailleur. Not to fret, it takes a few seconds to swap while you’re setting things up.

The installation was all cake from there. I removed my “old” GX kit and replaced it with Eagle 90. Boom. Done. The cassette mount is identical, as are the cranks and BB, and the shifter threads and clicks, just as they have been for most of my MTB career. Eagle 90 and 70 Transmission drivetrain bits are compatible with most existing Transmission parts, including T-type chains, cassettes, and chain rings.

The only head-scratcher was the derailleur adjustment. Once you set the derailleur in its proper spot, per the AXS app, dial in cable tension, and fiddle with one knuckle bit on the cage, you’re golden. There are no external limit screws to contend with. It’s just a mount and pedal sort of affair.

The cable-tension adjustment took a touch more finesse than other SRAM setups I’ve used. A click in one direction had the chain clicking between cogs, and the other direction was crisp and quiet. This is more a note than a complaint. The drivetrain simply wants proper adjustment, which is relatively simple to achieve.

With minimal time on the electronic T-type drivetrain, I didn’t fully realize how foolproof it all is. I don’t yet understand how there’s no need for high and low limit adjustments, and I’m okay with that ignorance because it works great.

Rebuildable and repairable

Like all of the battery-powered T-type derailleurs, these new parallelograms can be rebuilt and refurbished as things wear and break. On a new Eagle 90 derailleur, the B-knuckle, bushing kit, cage assembly, skid cover, P-knuckle kit, and pulleys can all be swapped out to keep your ride rolling.

Pedal impressions on the trail

Under heavy pedal power, the Eagle 90 drivetrain does exactly what it says on the tin. You can pedal hard and shift hard at the same time. No need to ease up or soft pedal to keep the cassette teeth happy. The chain and cassette know when and where they want to do their business. Your thumb action at the shifter isn’t necessarily making the chain move; rather you’re telling the drivetrain that you want a different gear when the time is right. That time will be blinking fast, with the slightest pause to wait for a ramp to realign all your muscle power to a different ratio.

Dumping to a lower gear comes two-at-a-time with Eagle 90, where the former SRAM mechanical drivetrains allowed riders to grab four gears with one push of the long-shift paddle. This adjustment may derail some folks who regularly ride undulating terrain, but in Bellingham trails mostly go up or down so I didn’t even notice this detail until our Editor-in-chief, Jeff Barber, asked me about it. This and waiting for the drivetrain to change gears are small tradeoffs for the Eagle 90’s ability to shift under full power.

All that clean power transfer is like driving a more refined car. My bike feels even better under me, and that’s saying a lot as this is the most fun bike I’ve ridden to date.

I haven’t dropped a chain in recent memory. I don’t run a chain guide, and both SRAM and Shimano derailleur clutches adequately hold my chain taught more than 90% of the time. Of the two brands, the SRAM clutch seems to keep the drivetrain a touch quieter and this new iteration is whispering along in its predecessor’s footsteps.

What I need more than a guide is a guard. Every season I buy a chain or chain ring after mistiming a compression or watching my wheel toss a rock into my drivetrain. I’m stoked to see these integrated rock bashers, and I’m motivated to bump into some downed logs to see just how sturdy they are.

Ergonomically, the shifter feels identical to my former GX levers, with a touch more grip for slippery or numb thumbs. It seems the tried and true recipe is just right with this one component. The new shifter features stealth routing like the new SRAM Maven brakes for a cleaner cockpit. It also uses a new cable pull ratio that’s not compatible with older SRAM mechanical derailleurs.

Lastly, let’s address this stupid thing that drivetrain manufacturers call “skating”. That’s the term for those times your chain drops down the cassette as you pedal backward. If you enjoy technical climbing, this is likely one of your most loathed drivetrain issues. You spin the cranks back to prep for a fun move, and all of a sudden the chain splays across the whole cassette and won’t budge. Kind of a bummer. Skating seems to increase as a drivetrain wears down, and while I haven’t worn much metal off these parts they have yet to skate around and mess up my uphill. I will report in the comments if that changes over time, but thus far I’m a happy turn-earner.

Eagle 90 Transmission specs, weights, and prices

Component	Weight	MSRP	Notes
Eagle 90 Derailleur	395g	$190
Eagle 90 Cranks	825g	$155	165mm, 32t chainring
Eagle 90 Shifter	135g	$50
Cassette (XS-1275)	445g	$250	Same cassette used by GX Eagle Transmission
Chain	285g	$50	Cut to fit. Uses GX Eagle Transmission Flat Top chain

Total	2,085g (4.6 Lbs)	$670 (Eagle 90 Complete)	Group price is slightly less than buying parts separately.

Direct mount for UDH bikes
T-type chain
Many parts repairable/replaceable
New cable pull ratio compared to previous mechanical shifters

Pricing for a complete Eagle 70 is not provided which suggests the group may not be offered for purchase initially. However, SRAM has provided pricing for individual components, so buyers could assemble their own group, or mix and match parts.

Final thoughts

I for one am happy to see mechanical shifting sticking around. Batteries and servos are fun, but its nice to see the advancement of affordable options like Eagle 90 and 70. The small tradeoffs that come with this new kit are well worth its performance advantages. Slightly slower shifts and two fewer dump-gears are things we can quickly adapt to and forget about, while the ability to shift while sprinting is something you’ll appreciate every time you hop on the bike. Add the easy setup steps and I would argue SRAM is leaving their competition in the literal dust.