Tern HSD S8i eBike Spec Review

In-Depth Review

Frame

The Tern HSD S8i is designed with a 6061 aluminum frame. If you’ve never heard of it before, 6061 aluminum frame is a strong alloy used in boats, automobiles, and even aircraft structures and components. As a result, the Tern HSD S8i is a resilient and durable eBike frame, though a bit on the heavier side at 55.9 lbs. However, this eBike frame is designed to work in almost any weather or environment, with the electronic cables and components safely protected so you can make use of the motor even in the rain. The frame is only available in one size, but the highly adjustable seat stem and other components makes it a great bike for most adult riders. If you are between 4’10’’ and 6’6’’, you should feel great and at ease riding the Tern HSD S8i.

The true highlight of the frame though is that it can fold! Folding takes just five seconds, and collapses down enough that you can easily throw the HSD S8i into the back of your car trunk. Most of the components are designed to collapse down, and you won’t have to worry about snapping wires or breaking the motor or electronic components as you collapse it down. However, you will want to follow the instructions along closely the first couple times you collapse the Tern HSD S8i down, and be aware that the pedals don’t fold in either. As long as you show a little proper care when storing the Tern HSD S8i, you’ll find it a great folding eBike option, though we do wish it was a bit lighter as well for easier carrying.

Motor & Battery

The Tern HSD S8i is a class 1 eBike with both pedal assist up to 20 MPH.

The Tern HSD S8i is powered by a premium mid-drive motor, which is our preferred motor style since it provides a biking experience that more closely resembles a traditional bicycle. Specifically, the HSD S8i is powered by a 250 W / 50 Nm motor, with a manufacturer top range of 70 miles, though some reviewers have found it could go 90 miles in ideal conditions. As a class 1 eBike, motor assistance is provided by pedaling, and when activated the Tern HSD S8i motor will assist you up to 20 MPH. After 20 MPH, the motor will shut itself off, but by continuing to pedal you will be able to exceed the 20 MPH speed limit. With a mid-drive motor, you can continue to pedal the eBike normally even when the battery is dead or off, though the downside is that if the mid-drive motor is damaged, you won’t be able to pedal the HSD S8i.

Overall, the motor performs well in flat terrain, but from discussing the HSD S8i with other reviewers, we’ve heard reports that it struggles in two situations. If you take the HSD S8i up steep hills, or if you load the eBike near its total 375 lbs weight capacity, the motor will not be able to hit 20 MPH on its own. As such, if you do hit a very difficult patch of terrain or are bringing a ton of extra gear with you, be aware you will likely need to help pedal in order to avoid overworking or quickly draining out your motor and battery.

In terms of charging the Tern HSD S8i, you are provided with the standard Bosch 4 amp charger. In order to recharge the battery from 0% to 100%, you will need an estimated 3.5 hours, making it real easy to recharge while you’re at work. The tube battery is easy to take off the eBike for indoor charging, though you can leave the battery on and recharge the battery while mounted as well. One more interesting thing of note is the battery’s position, located behind the seat and just below the cargo rack on the Tern HSD S8i. Stuffed between two support frame bars, the battery is out of the way and well protected, minimizing the damage it should when you suffer an occasional crash.

Display/Assist Modes

The small but reliable Bosch Purion backlit display is easy to read, with the basic functions and settings that you need to monitor your performance while you ride. The Purion display cannot be replaced, and it can be underwhelming for some eBike enthusiasts given the premium price tag of the Tern HSD S8i. However, the smaller, compact display doesn’t mess with your handling or distract you as much as larger display controllers, so the Bosch Purion is going to be a great controller for most people who ride the Tern HSD S8i.

Here is a list of key metrics and control settings you can monitor with the Tern HSD S8i electric bike:

Bosch Purion Display Metrics and Control Settings:

• Current Speed
• Assist Level (Four Levels and Walk Mode)
• Battery Level (Five Levels)
• Trip Distance
• Total Distance Traveled
• Estimated Battery Range
• Headlight Control

There are four motor power assist levels, which consist of Eco, Tour, eMTB, and Turbo. Eco mode provides the least amount of power assistance, but is the most efficient energy wise and will help you travel the farthest. Turbo mode will help you get to 20 MPH in seconds and is great for traveling up hills or transporting a lot of cargo, but will drain the battery the quickest as well. Tour is a bit more powerful than Eco, and eMTB is a bit more efficient than Turbo. Swapping your power assistance is easy and just requires a touch of a button, so experiment and vary your power settings in order to determine the best mode for your riding style and situation.

While it may not be a very advanced controller, the Tern HSD S8i is a great display controller for those who just care about key controller functions and don’t need any extra features.

Handling

• On Streets- This is a cargo bike meant for riding in the city, and that is where the Tern HSD S8i performs best. The bike is great on flat cement and pavement, and still rides well over cobblestone and the occasional uneven road thanks to the Suntour suspension fork. Due to the tire size and the folding design of the HSD S8i, be aware that you won’t feel as steady as some other dedicated suspension city bikes.
• Turn Radius- The wide tires aren’t great for turning quickly, but with the smaller height it does mean you won’t have too much trouble if you do need to pivot quickly. The Tern HSD S8i will have no trouble avoiding collisions with lampposts, cars, and other bikers, but you will need to take your time to turn if you’re going down a particularly narrow street.
• Low Speed Handling- The 35 Nm Eco mode and the walk mode are both great options for handling the Tern HSD S8i at low speeds. Use the eco mode for power assistance while riding at low speeds, with walking mode doing as the name describes by providing motor assistance while you’re walking. We definitely recommend making use of the motor assistance at low speeds, given the heavier weight of this 55.9 lbs electric bike.

Gears/DriveTrain

The Tern HSD S8i drivetrain consists of a Gates CDX CNC machined cog cassette, with a Gates carbon drive CDX belt and Shimano Nexus 8 shifting. This internally geared drive train features a belt drive system, which provides several great advantages over a traditional chain drive system. Belts are far less likely to drop or fall off when you’re shifting gears or are applying a lot of torque on the drive system, and they won’t damage the chainring and cassette teeth in the same way that chains gradually do. Gear shifting is all internal, making shifting a smoother and even quicker process. The Bosch motor shift detection system also checks your speed, cadence, and overall performance over a 1,000 times a second, further enhancing your drivetrain with precise and accurate control. The 8 speed shifting provided by the internal belt drive may feel limited to more advanced chain based eBikes, but it will be more than sufficient for the typical rider who wants a eBike to navigate city streets.

Brakes

In regards to the braking system, the hydraulic disc brakes are 180 mm front rotors and 160 mm rear rotors. These brakes are more than enough to help you come to a quick, smooth, and steady stop when the brakes are applied via the adjustable three finger braking levers. The Magura MT4 braking system is also well designed due to its integration with the Bosch motor system, as pulling on the brakes will automatically cut off the motor power. By doing so, not only will you come to a quicker stop, but you won’t have your brakes competing against the motor, the life of the braking system and motor system both extended with this integrated design.

Suspension

The Tern HSD S8i has a custom Suntour SR front coil suspension system, which provides solid shock absorption and support when you’re riding through the city. The Tern HSD S8i will provide very smooth riding when you’re on a flat, well built road, and it won’t shake nearly as much on cobblestone and the occasional rough patch of pavement as it would without the suspension. With 70 mm of travel, along with preload, compression, and lockout adjustments, you can configure the suspension to feel even better according to your personal riding preferences.

We would definitely recommend taking some time to configure your personal suspension, because some riders have reported the HSD S8i to be unusually jittery when you hit bumpy terrain. The 20’’ wheel size tends to ram into bumps instead of properly spanning around them, and the lack of seat post suspension does run counter to the front frame suspension when you hit rough ground. This is largely going to be an issue of personal preference though, as we expect the traditional rider to appreciate the suspension support that does come with the Tern HSD S8i electric bike.

Pedals

The Wellgo urban pedals are built with plastic and a non-slip rubber surface, though with a bit of extra weight support and steadiness thanks to the alloy core within the pedal. The pedals are large enough to support most traditional shoe sizes, and do come with reflective orange lights on the front and back perimeter of the pedals. As we have noted previously though, the one major strike against the pedals is that they do not fold into the Tern HSD S8i, unlike many other components on this folding eBike. While they are built tough, you will want to pay attention to how you set the eBike down, or you might end up accidentally damaging or even snapping the pedals if you don’t show proper caution.

Grips and Saddle

The grips are Ergon GP1 ergonomic rubber, providing a soft and cushy feel that won’t hurt or irritate your hands even if they get cold or sweaty from a long bicycling adventure. The grips are locked onto the handles, providing a solid feel while also making them easier to replace when compared to simple grips that are glued onto the handles. The handlebar itself features a swept-back design and measures 670 mm in length, and is the Tern Andros design capable of folding down and into the electric bike frame. The handlebars offer quite a bit of adjustability as well, which is why short and tall riders alike should feel quite comfortable riding the Tern HSD S8i electric bike.

The saddle itself is a Tern HSD branded Velo seat, designed with comfort in mind for both athletic trainees and casual commuters who just need an eBike to help them get to work. The plush saddle should be enjoyable to ride, no matter your size, and the highly adjustable stem further helps you get a better fit while riding the Tern HSD S8i electric bike. We do wish additional suspension support was included with the stem and saddle, but the suspension included as is with the Tern HSD S8i should be enough for most city commuters and casual bikers.

Wheels and Tires

Tires consist of Schwalbe Big Ben 20’’ by 2.15’’ tires, with double wall aluminum Tern Atlas H 32 hole rims and Sapim, stainless steel 14 gauge spokes. These tires have an inflation range of 30 to 55 PSI, and feature RaceGuard puncture protection that makes them very difficult to damage and pop. The PSI inflation range is a bit smaller than what we expected in a premium eBike, consisting of just 30 to 55 PSI. However, multiple reviewers and cyclists who have tried the Tern HSD S8i have noted that changing the PSI does make a difference, and that the lower PSI does make riding over bumpy roads and loose ground significantly easier. Overall, these are solid tires, and while they won’t do well off-roading, they will be more than enough for riding through paved city streets.

Accessories/Upgrades

There are a number of great accessories already pre-built into the Tern HSD S8i as a stock model, including high quality plastic fenders, a rear cargo rack, and a 190 lumens Tern Valo direct front light. However, the HSD S8i is also designed to be compatible with a number of other Tern accessories and upgrades as well. The HSD in its name comes from the phrase “Haul Stuff Daily,” which you will be able to do with accessories such as:

• Tern Cargo Hold 37 Panniers
• Term Kontti Basket/Market Basket
• Tern Short Bed Tray
• Tern Hauler Rack
• Tern Transporter Rack
• Tern HSD cache Box
• Tern Sidekick HSD Wheel Guard

Recommendation

The Tern HSD S8i folding electric bike will get you where you want to go when riding through the city, with a number of other great features that help it stand out from the eBike crowd.The 6061 aluminum alloy frame is sturdy and durable, but easy to fold while still providing up to 375 lbs of weight support for riders and their cargo. The class 1 motor will provide up to 20 MPH of assistance, with a solid range of 70 MPH and a removable battery that is easy to swap out and charge for an even greater riding range. While not the most advanced or feature heavy display in the world, the Bosch Purion controller has the basic functions you need to make full use of the Bosch Active Line Plus Gen 3 motor. What does stand out is the belt drive system, and while limited in speed options it requires far less maintenance than your typical chain based drivetrain. With great suspension and brakes thrown in as well, the Tern HSD S8i stands out as a premium city commuter eBike, though it does have a premium price tag attached to it that will cost even more if you add additional cargo racks and accessories. Even as a stock model though, the Tern HSD S8i will provide the performance and support you need to travel around the city with your gear, and is a great option for those shopping for a new commuter electric bike!