SRAM’s Eagle 90 Transmission might be the best MTB groupset yet for riders determined to minimise the number of batteries on their bikes.
When SRAM launched its Transmission drivetrains, they were lauded as the best-shifting, most reliable and most durable drivetrains on the market.
However, they relied on electrical power to shift up and down the cassette, and used rigidly defined timing gates to ensure every shift was as smooth as possible.
Many riders still wanted a digital-free ride, and some found the slow shifting a frustration (something recently sped up by a firmware update).
The inevitable march of electrification on our mountain bikes may have alienated some, who felt that high-performance mechanical parts would be consigned to the dustbin.
However, this year, SRAM launched two new mechanical drivetrains, Eagle 90 and Eagle 70 Transmission.
These use the Full Mount connection to the frame, which eschews the derailleur hanger, as per their electronically controlled Transmission AXS siblings.
The two mechanical drivetrains promised shifting performance nearly on a par with their electronic counterparts, but do they deliver?
All the options
While the cheaper Eagle 70 Transmission is targeted primarily towards OEM customers, the Eagle 90 Transmission, as tested here, is the option you’re most likely to see, both on bikes and in the shops.
The derailleur, shifter and cranks are branded as Eagle 90 products, with the chain and cassette borrowed from elsewhere – an XS 1275 cassette and GX Transmission FlatTop chain in this case.
Within the Eagle 90 family, there are a number of options to choose from.
There are two shifters – one that offers a double-click through the large alloy thumb padel, and one that's single-shift only – aimed at ebike riders, where multi-shifts are more likely to be mechanically unsympathetic.
Both mount to the bar either via a clamp, or onto SRAM brake levers via the Matchmaker bracket.
The alloy cranks also offer plenty of choice.
There’s an ebike version that mounts to SRAM, Brose, Bosch and ISIS-spindled motors, available in 150-170mm lengths.
There’s a ‘normal’ version too, as tested here, in 155-175mm lengths, which spin on a SRAM DUB bottom bracket.
Eight-bolt steel stamped chainrings attach with 30, 32 and 34t options, onto which chainring size-specific composite bash guards can be bolted. These are shared with GX and X0-spec chainrings (which use a three-bolt attachment).
Alloy chainrings can be specced, which should shave a little weight.
Finally, at the derailleur end, while there’s only one option, most parts of the derailleur can be replaced if damaged.
- B-knuckle replacement kit: £62 / $64 / €70
- P-knuckle replacement kit: £33 / $34 / €37
- Skid plate, outer and inner-link replacement kit: £33 / $34 / €37
- Cage and damper (clutch) assembly kit (also sold without the damper): £83 / $85 / €93
- Inner cage replacement kit: £27 / $28 / €31
- Pulley replacement kit: £17 / $17 / €19
- Bushing replacement kit: £18 / $18 / €20
And, if you want to upgrade to an electronic system down the line, there’s a GX Transmission upgrade kit available (£570 / $605 / €650), containing an electronic derailleur body (minus the cage, which you’d transfer over), shifter pod, battery and charger.
SRAM Eagle 90 Transmission component weights and prices
| | Weight (g) | Price £ | Price $ | Price € |
|---|---|---|---|---|
| Derailleur | 391 | 185 | 190 | 205 |
| Shifter | 132 | 50 | 50 | 55 |
| Chainset (165mm, 32t ring) | 734 | 150 | 155 | 170 |
| Bash guard, pair | 81 |
Weight comparison
| | Eagle 90 weight (g) | SRAM GX Transmission weight (g) | Shimano XT weight (g) |
|---|---|---|---|
| Derailleur | 391 | 491 | 283 |
| Shifter | 132 | 55 | 55 |
| Chainset (165mm, 32t ring) | 734 | 643 | 658 |
| Bash guard, pair | 81 | 81 | na |
SRAM Eagle 90 Transmission installation
If there’s one thing the shift to wireless groupsets brought about, it was the end of having to fiddle with cable tension and routing.
With Eagle 90, this has obviously returned.
Fitting the system is, however, fairly easy, because the Transmission architecture, forgoing a derailleur hanger, means there are no high and low stops, nor a b-tension screw to get right.
The shifting performance, however, relies on an exact chain length, and the derailleur’s main bolt and rear axle being tightened to the correct torque while the chain is routed over one of two sprockets on the cassette.
These two factors are bike-specific and can be found via the (unusually for the bike industry) very good SRAM AXS app.
It is also dependent on two line markings – one on the metal plate that sits between the main derailleur body and the dropout, and one on the derailleur, to line up. It’s all part of the fitting process, and the main stumbling block when it comes to setup error.
To hold the derailleur in place during setup, a 4 or 5mm Allen key needs to be inserted into the derailleur’s parallelogram, to counter the spring’s pull. It feels a little Heath Robinson, but works effectively enough.
It’s then a case of routing your cable and securing it.
In theory, that should be it, with perhaps the smallest tweak of cable tension via the barrel adjuster on the shifter.
As with any cable-based system, you may have to battle cable tension for a week or two once it has stretched a little after the first couple of rides. However, in my experience, this settles down pretty quickly.
SRAM’s step-by-step installation guide is very good and worth following to the letter.
SRAM Eagle 90 Transmission performance
I fitted Eagle 90 to my long-term Last Glen test bike, pretty much as soon as it was available in March 2025. Over the past six months, I’ve ridden it multiple times per week, with minimal TLC.
It’s done plenty of miles around my usual stomping grounds in the South West of the UK, and faced a week of epic proportions in the Alps, where it came away with more than one battle scar.
I’ve found the shifting across the cassette to be excellent.
While its electronic counterparts are programmed to shift when the chain is ideally located over the shift ramps on the cassette, causing a delay, Eagle 90 is ‘dumb’ and so shifts as soon as the shift levers are engaged.
Despite this, the engineers at SRAM have done a good job of shaping the cassette teeth and chain plates on the GX-level kit, with the two marrying up to provide a generally smooth and reliable shift up and down the cassette, even if your manual timing isn’t perfect.
There are times when there’s a bit of a clunk as the chain drops into a smaller sprocket, and very occasionally there’s a grumble as it’s pushed onto a larger sprocket.
But in the vast majority of cases, the shift is smooth and accurate.
The shift even feels sturdy when you’re putting in more effort than it feels you should. Here, while I can’t prove it, it feels as though the stiff construction of the Full Mount design is doing a good job.
Thumb feel
At the bar, the shifter feels… OK.
I’ve never been a huge fan of SRAM’s mechanical shifters, preferring the feel and ergonomics of Shimano’s offerings, especially at XT or XTR level.
Although the shifters' construction is sturdy enough, I find Shimano offers a slightly more direct and accurate lever feel. I also prefer the dual-release function on the XT and XTR shifter – something that's lacking on Eagle 90 Transmission.
Given that a Shimano XT shifter is available for around £40 in the UK, £10 less than the list price for Eagle 90’s, this is a touch disappointing.
Furthermore, I’ve found the band-clamp fitment is better than Matchmaker options. With my preference for a flatter lever position, I struggle to get the shifter positioned far enough under the bar for an ergonomic position.
Keep cranking
At the cranks, there’s little to complain about.
They’re not the lightest cranks around, although they are cheap, stiff and dependable. The eight-bolt chainring fitting is a bit frustrating, limiting after-market options a little, but the steel chainrings are showing few, if any, signs of wear after six months.
The bolt-on bashguard is effective, however it is chainring-size specific, so if you go up or down in tooth count, you’ll need a new one.
It is definitely worth using anti-seize around the main crank bolt, though, because these have a habit of binding on. You may need a scaffold pole to remove your cranks if you leave them attached over a long period.
SRAM Eagle 90 Transmission reliability
After six months of use, I would be disappointed, though not entirely surprised, if there was some notable wear and tear on a drivetrain.
I’m happy to report, though, that so far Eagle 90 has proved utterly reliable.
Early on, there was some clicking and slight bumpiness from the chain running over the third biggest sprocket.
However, this has disappeared in time, leaving a smooth, quiet and dependable drivetrain, even with minimal care and attention.
The chainring’s steel construction might not be light, but it has resisted wear well, and the cables feel fresh after a summer of dry and dusty conditions.
There’s no undue wear on the chain, nor any corrosion present.
Cranks these days seem to scuff up pretty quickly, with SRAM and Shimano some of the worst in my experience.
However, while there is some light scuffing to the black anodised crank arms, they still look moderately smart and wear-free.
Perhaps most impressive is how resistant to damage the rear derailleur seems to be.
In the Alps, the derailleur took a number of sizeable hits, from the front onto the main knuckle and cage.
The mullet setup of my bike, and the low-hanging cage seem to leave it susceptible to impacts. This has left the parallelogram and cage scraped and scarred.
However, other than superficial damage, there has been no lasting, performance-detracting damage.
Instead, the whole derailleur rotates back, preventing permanent harm.
No, the bike can’t be ridden like this, but with an 8mm Allen key for the main bolt and the appropriate one for the rear axle, the system just needs resetting before it carries on working.
After a hit and reset, I would recommend resetting the torque of the main bolt as soon as you have access to a torque wrench, though.
My experience of all Transmission derailleurs is that if the bolt isn’t tightened appropriately, they can migrate with use, upsetting your shifting performance.
All this said, though, if damage was to occur, it’s great that so many parts of the derailleur are replaceable.
SRAM Eagle 90 Transmission bottom line
Back when mechanical shifting was ubiquitous, I was always a fan of Shimano’s efforts. However, in the past couple of years, I’ve become quite impressed by SRAM’s electronic offerings.
Their shifting has always been incredibly reliable and smooth, even if I haven't loved the new Transmission Pod shifter modules.
I didn’t expect to love SRAM Eagle 90 Transmission. However, I’ve come away mightily impressed.
The shifting is very good, I haven't had to charge a battery and I’ve been more than happy with the reliability.
Yes, the cranks are a little weighty, and the shifter still isn’t as good as Shimano’s offerings.
But I’m in no rush to replace the groupset on my bike, despite having a number of electronic offerings stacked up waiting in my garage.
Product
| Brand | Sram |
| Price | £655.00 |
