I liked it a lot. So much I ordered one for myself.
I was also curious to the geometry and linkage, the suitability for a coil shock and other stats. I contacted Andre XTR who provided the following data on the suspension analysis on the 2022 Trek Rail. I have attached it below with his permission.
==== ANDREXTR Data (close approximation, since the schematic drawings were not available in this case) ====
Trek Rail 9.9 2022 – low position
Travel: 150mm with the 230 x 57.5mm shock
LEVERAGE RATIO
Trek Rail 9.9 2022 has a moderately progressive suspension curve. Considering the amplitude and the shape of the leverage ratio curve, the final progressivity is 30%, meaning that it takes more 30% force to bottom-out comparing to any fully linear bike equipped with the same shock and SAG% (example of linear bike is for instance, Orange Stage). For more info about these calculations check my video HERE. Another interesting point is that the curve is almost a straight line, without fancy shapes, so the progression builds in a very constant and predictable way across the travel. This makes the Rail suitable for both coil and air shocks.
The Rail leverage ratio continues decreasing with the same shape and slope even if you increase the shock stroke up to 65mm (on low setting in the flip chip). However, with a 65mm stroke (at low) this will almost certain create a problem of the seatstay bridge hitting the seat tube at bottom-out. You have to run the bike in the high mode (even though you need to check very carefully for clearance).
On higher mode, you lift the rear end of the bike by basically creating and adding more ~9-10mm of wheel travel at the beginning (when compared with the 0mm position of the low setting). So, on the high setting if you compress the rear suspension by 9-10mm you end up with the same geometry of a fully extended low-setting bike. Its seems that the overall travel also increases by around 5-6mm on the high setting (so you end up with around 155 mm with standard shock).
Using a 65mm stroke might boost the travel to around 175mm, which is a bit too much in my opinion. Keep in mind that a 57.5mm stroke is usually a 65mm shock restricted with a 7.5mm spacer (travel reducer) pre-installed. There are 3 sizes of travel reducers: 2.5mm, 5mm and 7.5mm. In this way manufacturers can cover a wide range of strokes by just producing a 55, 65 or 75mm shocks for instance.
Considering that the average progressivity for most 150-160mm enduro bikes on the market is around 20-30%, and for DH bikes is around 40%, we can consider the Rail as a moderately progressive trail/enduro bike, and it is within the normal numbers for its segment. This amount of progression will make the Rail a good fit for most of trail/enduro riders (it’s neither too linear, neither too excessively progressive).
Ideally the frame progressivity should match with the aggressiveness of the riding style (and not with rider weight!). So, for more aggressive riding styles (eg: bigger impacts, drops, jumps, DH tracks or red and black tracks) a more progressive suspension works better (it provides more bottomless feeling with less sudden and harsh bottom-outs and with more control under heavy impacts), while for a more “normal” trail riding, like flow-trails, green and blue tracks, smooth jumps, natural tracks like rocky trails without big impacts, a less progressive suspension works better because it allows to use the final part of the travel more easily (the whole travel is more “usable”).
So, for less aggressive riding style, too much progression can result in a useless final part of the travel, while for more aggressive tracks and aggressive riding styles, a progression of 40% (or more) will be a better fit.
For a 150mm e-bike, I think the Trail has a good compromise on the frame progression (of course that on top of that you can always increase the overall progression by reducing the shock internal free volume via tokens/spacers, however, the base progression of the frame is very important to contribute to the overall final progression).
Pedaling efficiency
In simple words, anti-squat is an intrinsic property of the linkage that counteracts the pedal- induced bob and determines the pedaling efficiency. Every time that shock compresses and extends due to pedaling (pedal bob) it means that your energy is being dissipated and wasted by the suspension and not to propel you forward. Most trail and enduro bikes in the market have near 100% anti-squats on average now-a-days. A 100% anti-squat value is defined as the “gold-standard” value in which the rear suspension does not extends neither compress under acceleration.
While this is true for motorcycles and cars where you only have horizontal acceleration forces (from wheel torque), on mountain-bikes you also have vertical forces during pedaling from the body and legs movement (up and down), which inevitably cause some sort of pedal bob even with 100% anti-squats. On E-bikes the pedal bob problem is attenuated because the motor helps keeping a smoother a more constant acceleration.
For a 30% SAG and for a stock 34T chainring, the Anti-squats of the Trek Rail 9.9 are very well optimized with numbers very close to 100% across all rear cogs on SAG zone (the pedaling zone). This result is because Trek works as a single pivot regarding anti-squat (the wheel is mounted on chainstay which is directly connected to the main frame by one pivot) and they placed the main pivot crossing with the chainline at the top of chainring height. If they placed the pivot lower the anti-squats would be lower, and if they placed the pivot higher, the anti- squats would be also higher.
Chain extension, pedal kickback and axle path
Regarding the chain extension, or chain growth, the maximum upper chain extension is 23mm at bottom-out (in other words, the distance between rear axle and BB increases by 22.5mm until bottom-out). Most bikes, on average, have a chaingrowth of 1.5 mm per each 10mm travel. So, Rail is exactly on the average with also 1.50mm per 10mm travel. These values of Rail were expected, since chain extension is proportional to anti-squats, and since Rail has very well optimized anti-squats (similar to most modern trail/enduro bikes) the chain extension is also on the average.
As a consequence of this chain extension, the pedal kickback of Rail should be normal and similar to most 150/160mm enduro bikes. Kickback is also related with chaingrowth.
Kickback happens as a result of the upper chain being “stretched” during suspension compression, which either forces the cassette to spin forward or pushing the cranks backwards counter- clockwise (hence the term “pedal kickback”). Kickback is mostly felt on big rear cogs (like the 50T) at slow bike speeds and when the chain is under tension (so, kickback is mostly felt during technical climbs).
On descends, usually you don’t feel kickback (not only the kickback is much lower on the smaller rear cogs, but also, at faster bike rolling speeds the freehub accommodates the chain extension by allowing the cassette to freely rotate forward and youwon’t feel the kickback in the pedals).
Regarding the axle path arc, it’s a forwarded skewed arc. The travel path is slighty rearwarded with only 2mm of horizontal displacement until SAG point, and then, it moves 16mm forward until bottom-out. Many bikes have a similar shape of axle path. To achieve a fully rearwarded path you need a high-pivot or virtual high-pivot design, with a chain idler.
Please note that the graph bellow is not scaled in proportion to better view the shape. The real shape is almost a straight line (see red line tracing the axle path bellow). To better visualize the picture you need to imagine the main frame in a static and fixed position (only rear wheel moves up and down).
Braking
The braking forces of rear wheel can slightly affect the suspension. This is called “anti-rise”. The higher the anti-rise the more the braking forces tend to compress the rear shock, but the less the bike will pitch forward under rear wheel braking. With lower values (~50% or less) when you brake the rear wheel the shock will slightly extend and the bike slightly pitches forward (because your mass transfers forward due to inertia).
With 100% values nothing happens when you brake the rear wheel (the anti-rise effect equals your mass transfer, so the forces cancel each other). With 150% anti-rise the shock will compress with rear braking (the anti-rise effect outweighs the mass transfer). This is something that can be easily tested on a flat tarmac surface after braking with rear wheel only.
Trek mounts the brake caliper on the seatstay, which makes it technically to behave the same as a horst link (the seatstay is connected to the main frame by both rocker link and chainstay). And since chainstay and rocker link are almost parallel, the resulting anti-rise is quite low. In other words, the brake caliper almost does not rotates around the disc when the suspension is compressed.
Trek ABP was a good marketing move back them in 2008, or so, and by using a concentric axle with the horst link pivot, they basically achieve the same benefits of the Specialized FSR without violating the patent.
Trek Rail has an anti-rise at SAG zone of 45%. So, Rail should provide an active suspension over bumps while applying the rear brakes, however, it has a slight tendency to pitch more forward during braking. So, assuming that there is always a trade-off between suspension full independence from braking (0% AR) and geometry preservation (100% AR), the Rail provides a good balance between both (although the topic of which anti-rise value is the best is still highly controversial on MTB).
CONCLUSION – Trek Rail 9.9 2022
Overall, the Trek Rail 9.9 2022 is a very well balanced e-bike with a moderate amount of progression considering its travel (150mm), and this will fit quite well a wide range of riders. The bike also provides a very good pedaling platform with anti-squats optimized in turn of 100% numbers. The chain extension and kickback values are perfectly normal, and the anti-rise (as expected) sits at nearly 50% providing a good balance between traction and geometry preservation.
Last edited:
