Trek Powerfly FS+ 4 Gen 4 800Wh 2026 - Mercury / Dark Web

Below is the recommended sizing for the Powerfly FS+ 4 Gen 4. Here you should measure your height with your shoes off.

Please Note: Many bike brands' size guides overlap slightly. This is because small adjustments like seat position can accommodate riders who fall between sizes. When you're in this overlap zone, the choice comes down to preference: a larger size for a more stretched-out ride, or a smaller size for a more compact feel.

At MTB Monster, we help customers on a daily basis choose the right size bike for their needs. We consider your measurements, riding style, and past bikes to help recommend the best size. If you're in doubt at all or want to just confirm your thoughts please contact us and we would be glad to help.

Frame Protection in our opinion is money well spent. Your bike is an expensive investment and frame protection helps to protect your paintwork from scratches, scuffs and chips to keep your bike looking spotless for years to come. In essence, frame protection is a custom cut, self-healing frame protection film made from Lotus Pro 10 - 10.3mil thick TPU film (or similar) designed specifically for mountain bikes and electric bikes. It features a ceramic-embedded hydrophobic top coat that effectively repels water, mud, and dirt, making post-ride cleanups faster and easier. Kits are available in both gloss and matte finishes and unless specifically requested we would fit the kit to match the finish of your paintwork. Some bikes have a mixture of matte and gloss paintwork and in most cases mixed finish kits are available. The material of a frame protection kit will act as an extra layer of clear coat and can make the finish of raw carbon more prominent due to the way that the light refracts. Similarly, fitting a matte finish kit can produce a more satin finish and mean that the kit is slightly more visible than when it is installed in a gloss finish.

Currently there are 3 options available

1. Supply and fit.

Our trained and experienced mechanics can install frame protection kits here so that your Powerfly FS+ 4 Gen 4 2026 arrives fully protected and ready to ride. We recommend a 48 hour curing period to ensure that the film adheres properly to the frame, so your order will take a little longer to arrive — but it will be well worth the wait.

2. Supply Only.

If you choose to install the kit yourself, we'll provide you with the kit, instructions, and a squeegee. Just select "Supply Only" and your kit will arrive with your bike — there is no delay to dispatch with this option. There are many informative videos online to guide you through installation. We would advise watching these in advance to see if you feel confident to fit the kit. Patience is a must when it comes to installation.

3. N/A.

Choose this option if you would prefer not to have frame protection fitting.

Please note: If no frame protection kit has been designed for the bike yet, no option other than N/A will appear. However, there is a very good chance we may still be able to get one designed or custom templated to fit. If this is of interest, please contact us here and we can look into it as soon as possible.

So, what's a tubeless setup? Traditionally, inner tubes are inflated with air to create a cushion between the rim and tyre. In contrast, a tubeless setup ditches the inner tube and relies on a specially designed rim with an airtight seal. A self-sealing liquid is added directly inside the tire, and air is pumped through a special valve to inflate the tyre. This allows riders to run lower pressures for better grip and comfort, and the sealant can plug small punctures on the fly, reducing flats.

However, it's important to note that bike manufacturers send their bikes to us in varying degrees of readiness to be set up tubeless. For example, some may supply suitable tubeless-ready tyres, but not the valves or sealant, while others arrive with everything you need. So here at MTB Monster we've checked and answered the following two questions;

Can the Powerfly FS+ 4 Gen 4 be set up tubeless? Yes, this bike can be set up tubeless.

What option do I need to select, if I want the bike setting up tubeless before I receive it? Your bike is set up tubeless from the factory. If you’d prefer inner tubes instead, please let us know.

In the box, you'll find your owner's manuals with your Pre-Delivery Inspection Checklist, signed off by our Cytec qualified mechanic. This details all the checks that have been completed along with an 'Important Information' sheet explaining the advised pre-ride checks to be carried out to ensure the bike is safe to ride and that it will perform at its best. We advise keeping this document safe in case it is required in the future.

We also include a bike battery charger with a UK specific plug for the Powerfly FS+ 4 Gen 4, the relevant allen keys to assemble your bike (normally 2), brake separators to keep your brakes apart whilst the wheel is out of the bike along with any manufacturers manuals, and any extras the brand has included. Some manuals are now only accessible online and paper copies are not included, if you require any assistance accessing manuals for your new purchase please get in touch.

It is worth being aware that bikes are rarely supplied with pedals included. This information will be detailed in the specification of the model you choose. If your bike is not supplied with pedals and you don't currently have any suitable ones, we have a great range on offer here

Any promotional freebies such as an MTB Monster mudguard will also be included in your box.

If you feel you are missing any parts of your kit please contact us within 24 hours of delivery so that we can help.

Showroom Viewing

While we showcase Trek e-bikes and often have the Powerfly model on display, we can't guarantee the exact bike you see online will be ready to view at any given time. This is because bikes might be recently sold, boxed in our warehouse, or still with the manufacturer. To ensure you see a specific bike you're interested in, please contact us before your visit & we'll do our best to have it available on the day of your visit or make alternative arrangements.

Can I demo & test ride the Powerfly FS+ 4 Gen 4?

We stock a wide variety of electric mountain bikes (eMTBs) for you to test ride at our showroom in the North-West of England. Our selection features various sizes, brands, and motor options, allowing you to compare different types of eMTBs – from standard models to lightweight ebike options. We offer test rides ranging from quick car park loops to more in-depth demos, tailoring the experience to your needs.

To see whether the Powerfly FS+ 4 Gen 4 is available to view or try out, please contact us & we do our best to arrange something with you prior to your visit.

The Powerfly FS+ 4 Gen 4 is classed as a cross country bike, designed for speed and efficiency on the climbs, perfect for covering longer distances quickly due to a lightweight frame.

Like all Electric mountain bikes they can be used on gravel paths and forest tracks, but the bike will really excel on smoother, single-track off-road trails with minimal technical features. Can be used for both road and off-road riding.

Absolutely! All ebike systems are designed from the ground up to live in the harshest conditions of mountain biking. You don't need to be concerned about riding the bike through a British winter, or in fact a British summer. In fact, these bikes are fully rainproof, ready to tackle endless puddles and wet, muddy trails without hesitation. The system utilises automotive grade electric ports and specifically designed covers to protect the system while providing the best weather protection so that you don't need to worry about riding in UK conditions. .

While the Powerfly FS+ 4 Gen 4 is designed with waterproof weather protection at the forefront, we would advise to avoid situations which would submerge the bike for any duration of time and against pressure washing the bike...just like we wouldn’t advise for a regular bike.

Cleaning an ebike is no different to cleaning a regular bike, a brush and hose pressure method is the best way. We advise against using a pressure washer as this often drives water behind seals, washing grease from bearings and also forcing water into electrical components. It's also best to avoid any harsh chemicals or abrasive cleaners as these can damage the finish of the frame and components. MTB Monster offer a range of recommended cleaning products that are designed for ebikes and non-ebikes.

Over the past four decades, Trek have been at the forefront of the industry, continually challenging the limits of bike design in order to be a manufacturer that builds bikes that people love.

Trek haven’t just stumbled upon being one of the largest and most respected bike brands in the world by chance. Through their commitment to quality, performance and customer care, Trek have built a solid reputation, befitting of their bikes. Our staff ride Trek’s so if you want to know any details that only an owner would know, let us know and we will be happy to help.

Getting started can seem daunting but there's only a couple of kit items that are essential for a safe and self-sufficient bike ride.

Above all else, a helmet is the most essential piece of kit. It dramatically increases safety when you're out riding. To put this in context, if you visited a UK mountain bike trail centre, you'd be hard-pressed to find anyone riding without one. Rider protection wise, this can be extended to gloves, knee pads and elbow pads depending on type the terrain that you are looking to tackle.

We would always recommend riding with a spare inner tube, tyre levers and pump. Most riders have a story about the time they got caught out with a puncture, usually in horrible weather and miles from the endpoint of the ride, learn from our mistakes :) Additionally, a number of mechanicals can be resolved on the trail with a handy multi-tool, these usually contain a range of hex keys, torx keys and occasionally a chain breaker to help you get to the end of the ride and into a fully equipped workshop.

For any additional advice, feel free to contact us and we'll be more than happy to help.

In the UK, you can ride an ebike anywhere that you would ride a normal pedal bike.

There are no restrictions in trail centres to prevent you from using an ebike anywhere that you would use a regular bike without assistance.

Local to store, we have Longridge Fell, Gisburn Forest and also Darwen Moors & Rivington. Within around an hours drive, you have the Lake District, North Wales, Yorkshire Dales & the Peak District offering a wealth of amazing riding opportunities. If you're ever looking for a route nearby, let us know and we can point out some highlights.

Throughout the wider UK, there are over 20,000 miles of bridleway and over 16,000 miles of national cycle network. Additionally, canal paths, forest roads and cycle lanes all offer a great network to connect your ride and minimise the amount of time that you need to ride on busy roads. A good starting part to find some fun mountain bike specific routes that cater for all abilities are trail centres. These are designed specifically for mountain bikes and are often located through the UK's many forest areas. Some great websites to check out as a starting point are; mbwales.com (Wales), dmbins.com (Scotland), forestryengland.uk/cycling (England) and mountainbikeni.com (Northern Ireland). One of our personal favourite riding spots at MTB Monster, is within the Tweed Valley area in Scotland, where the design of the tracks are simply world class and cater for all abilities.

If you scroll up the page to just below the image, you will see a green tab labeled 'technical' containing the specification of the bike with all of the componentry details on the Powerfly FS+ 4 Gen 4.

Alternatively, click here to go directly to this tab.

Yes, a water bottle can be mounted to the downtube.

Frame:

Every Trek frame carries a lifetime warranty with a generous crash replacement scheme should the worst happen out on the trails..

Components fitted the bike

All components fitted to the bike are covered under warranty by the respective manufacturer which is typically two years however in some cases, this can vary and items such as suspension are subject to servicing being carried out.

Electrics

Bosch offers a 2 year warranty on the motor, battery and the ancillary parts required for the system to operate such as the display, speed sensor and wiring.

Whether or not a bike is supplied with pedals is at the discretion of the manufacturer. If you select the technical tab on any product page you will see 'pedals' as a one of the items and here it will tell you if they come as standard from the manufacturer. By reducing the number of components included with a new bike, manufacturers can minimise waste and packaging. With so many different types of pedal available it's unlikely that anything manufacturers include will suit everyone. If you require pedals and they are not listed as included in the specification of your chosen bike you can find the range that we offer here and of course if you are unsure please get in touch for some friendly advice.

Yes, all of the brands we deal with carry a large number of spare parts to support their customers. If you have purchased a bike from MTB Monster, our rider support team will work with you and the team at Trek to get you the parts you need as soon as possible.

The electric bikes that we sell at MTB Monster are completely legal to ride in the UK, both on-road and off-road. The maximum speed that an ebike can be assisted to in the UK is 15.5mph (25kph). It is easily possible to ride an ebike faster than 15.5mph but the motor will not offer any assistance beyond this point. The Powerfly FS+ 4 Gen 4 is set at the maximum level of assistance permitted in the UK.

Pedal bikes with electric support up to 15.5mph (25 km/h) are regarded as equivalent to bicycles by law and therefore, do not require vehicle insurance, a registration plate or a driving license

Yes most upgrades on the Powerfly FS+ 4 Gen 4 are fine, if you fancy changing the brakes, adding some blingy new grips, or maybe a change of fork, you're welcome to make these changes. However, just make sure they are both suitable & compatible with the bike.

Please note with E-bikes:

Changes in gearing or wheel size will need to be reflected in the motor programming as this can affect speed ratings, and this is where it starts to get tricky as it will require the brand's authorisation. Typically changing anything to do with the motor system of an electric bike is not recommended unless advised otherwise by the bike/motor manufacturer.

How you store the Powerfly FS+ 4 Gen 4 is pivotal for maintaining its condition and ensuring the e-bike is ready to go when you are. Ebike's should be stored clean and dry in a cool environment between 10 to 20°C, with the battery level between 30-60%.

If a battery is ever stored separate to your bike, again make sure it's stored in an area without significant temperature fluctuations. Somewhere that endures extreme temperature changes – such as an outdoor shed for example.

Batteries are highly complex components and are designed to offer a long service life. The service life of the battery is influenced by several factors such as the amount of charge cycles, intensity of usage, charging practice and storage temperatures. That being said, under typical use of going out riding a few times a week, you should expect to get a couple of years of riding without any problems, as that has been our experience for 99% of the ebikes we have sold to date.

Also it's worth bearing in mind, we still have plenty of customers riding bikes purchased over 5 years ago with the original battery, and very rarely do we have customers complain about battery issues. And for peace of mind, if anything was to happen, the batteries themselves are covered by warranty for the first 2 years of use.

Lithium-Ion batteries are, provided certain precautions are met, are safe.

The high-quality lithium-ion batteries fitted to our range of e-bikes are equipped with a Battery Management System (BMS) which is continuously acting to detect potential sources of error and protects the cells from overload, undervoltage, overheating and short-circuiting.

According to the Bicycle Association there is a very low risk from un-modified legal Electric Assist Pedal Cycles (EAPCs – street-legal eBikes) if bought complete with their approved batteries and chargers, from reputable brands, sold by reputable retailers, and handled according to the manufacturer's' instructions.

All of our bike brands we sell, and the electrical componentry they use on their e-bikes, are fully regulated and adhere to the highest standards. It's also worth noting, that they are simply worlds apart in terms of safety, when compared to cheap unregulated imported e-bikes that you would find on any online auction sites.

Yes, the battery can be removed from the bike for easy charging and for safe keeping. The battery will be locked onto the frame and will require the keys supplied with the bike to fit or remove the battery.

Type of E-Bike - Mountain e-Bike.
Stop frequency - Bike ride with few breaks.
Terrain - Hilly.
Wind Conditions - Light breezes.
Average Speed - 10 mph.
Surface - Gravel and surfaced forest paths.
Tire tread - MTB tires (Enduro).
Cadence - 60rpm.
Season - Summer.
All data is generated through the official Bosch Range Cockpit. For personalised results please contact us

A range extender offers an extra safety net of battery power for those longer days in the saddle. Bosch offers a range extender for the Powerfly+ which packs 250Wh within 1500g, the Range Extender can be easily mounted in the water bottle holder.

If we have the range extender in stock, we will add a purchase link on the technical tab of the product page (next to range extender) to add to your shopping cart if required.

For fire safety, couriers have restrictions that prevent the shipping of electric bikes with more than 30% charge. This will be more than enough to take your new bike for a quick spin but the bike will require a full charge prior to your first proper ride

The battery is integrated in the downtube and is charged through the port on the frame.

The best practice is to firstly connect the charger to the charger port then plug into the wall socket. This way the charger will automatically switch on and start charging your battery when connected to the wall socket and switch off supply once the bike is fully charged therefore preventing overcharging the battery. As the battery is charged the display (if fitted) will also be charged up at the same time.

TBC.

The motor on the Powerfly FS+ 4 Gen 4 is protected by a plastic guard which will shield the motor from the worst of the trail conditions and will act as a sacrificial part to protect the motor from impact should you require it.

★  4.9 / 5 Google Reviews

★  Free front mudguard with every bike

★  We accept most Cycle To Work schemes

★  All bikes built by Cytech qualified mechanics

★  0% APR finance available (subject to status)

Yes you can spread the cost of your new Powerfly FS+ 4 Gen 4, with 0% APR financing, we offer this on all our bikes, making monthly payments more manageable.* For many of our higher-priced products, the option of 0% APR financing for up to 48 months is also available*.

MTB Monster offers financing options through a number of various providers to help you spread out the cost of your new e-bike. Here's how to find the details:

- Locate the boxed area titled "Finance Options" situated below the "Add to Cart" button on the product page.
- This section will list the different financing providers MTB Monster partners with.
- Click the "Learn More" button next to each option to explore the specific terms, including interest rates and monthly repayment terms offered by the provider*.
- With multiple finance options to choose from, we suggest opening all of the “Learn More” links to discover the ideal plan for your needs.

By following these steps, you'll gain all the necessary information to determine if financing your Powerfly FS+ 4 Gen 4 purchase is the right choice for you.

* Remember, terms and conditions apply, and approval is subject to your status

Yes, we accept Cycle to Work vouchers for the Powerfly FS+ 4 Gen 4 from all the major providers.

Cycle To Work is a government initiative which offers the most cost-effective way to purchase a new bike. It's fundamentally a salary sacrifice scheme meaning that the repayments for the bike are deducted out of your wage before tax and national insurance saving you between 33% and 43%!

The first step is to contact your HR department or your accountant to check that you are eligible to access a voucher and discuss any questions that you might have about how the scheme is run at your workplace.

Once you have confirmed that you are eligible for a voucher, it's best to place a £200 deposit here to reserve the bike of your choice to prevent stock from selling out while your voucher is being arranged.

You are more than welcome to place a £200 deposit to reserve the bike while you are finalizing your payment method to prevent the bike from selling out in the meantime.

We are more than happy to reserve a bike for up to 3 weeks but please let us know if you need us to reserve the bike for longer so that we can best know your situation and accommodate this.

If you want to place a £200 deposit, please fill out the options on the product page to reveal a pre-order button (see image below).

Absolutely, the best way to reserve a new model is to place a £200 pre-order which will reserve an allocation to receive one of the first bikes. Without a deposit in place, there is a good chance that the bike may sell out before it comes into stock.

If you want to place a £200 deposit, please fill out the options on the product page to reveal a pre-order button (see image below).

The following 2 links demonstrate in detail the answers to this question:

How your bike is packaged

How to build your new bike

If you scroll up the page to just below the image, you will see a green tab labeled 'Collection & Delivery' containing all of the information required for collection & delivery.

Alternatively, the information is also availble on our 'Collection & Delivery' page.

You are more than welcome to collect the bike in store. This is a great option if you are unfamiliar with some of the technology on the bike. We can run through a full handover and you can pick our brains to answer any questions that you might have about some of the systems or technology on the bike, the best accessories for the bike and also all the best local riding spots.

Yes of course, we'd be happy to help, either call us or contact us