Our readers keep the lights on and my morning glass full of iced black tea. As an Amazon Associate, I earn from qualifying purchases.
Specs are compiled from manufacturer listings and verified buyer reviews and can change over time — please confirm the key details on the product page before buying.
Buying a bike frame is different from buying a whole bike, because you are choosing the skeleton everything else bolts onto. Get the dropout spacing or the seat tube size wrong and your motor, wheels, or fork simply will not fit. Get it right and you can build a commuter, a lowrider showpiece, or a high-power electric mountain bike on one solid foundation. This guide breaks down four frames people actually build on, so you can spot the one that matches your parts pile.
I’m Min — the founder and writer behind Gadgets Feed. This guide is built by comparing the manufacturers’ published specifications and the patterns across verified customer reviews, so you get each pick’s real strengths and trade-offs instead of marketing spin.
The frames below span aluminum full-suspension, steel lowrider, tank-in-frame gas builds, and heavy steel electric platforms. The trick is matching frame numbers to parts you already own or plan to buy. That match is exactly what separates a smooth build from a box of parts that never bolts together, and this guide walks through the best bike frame options for each kind of builder.
Our Picks at a Glance
How To Choose The Best Bike Frame
Before you buy any frame, you need to know three numbers about the parts you already own. Those numbers decide whether your build is a weekend project or a month of drilling and re-tapping threads.
Start with your rear dropout spacing
The dropout is the slot at the back of the frame where your rear axle sits. Its width must match your wheel or hub motor. A frame built around 135mm spacing fits a standard rear hub and many hub motors, while a 150mm or wider dropout takes bigger, more powerful motors. If you already own a hub motor, measure its axle width first and buy a frame that matches. Forcing a wider motor into a narrower frame means bending steel or skipping aluminum entirely.
Check the seat tube and head tube
The seat tube inner diameter sets which seatpost slides in. A common size like 27.2mm opens up a huge choice of seatposts, while an odd size like 26.8mm narrows your options fast. The head tube is the front tube your fork steerer passes through, and it carries its own sizing. A stated 1 1/8-inch head tube fits the most common fork standard, so you are not hunting for a rare part.
Decide aluminum or steel
Aluminum frames tend to be the lighter option for a given strength, and they resist rust. Steel frames are heavier but can be welded, braced, and bent by a home builder, which is why high-power electric builds often lean steel. Neither is wrong; they just suit different jobs. A commuter with moderate power rides well on aluminum, while a heavy motor and long-range battery often calls for steel’s forgiveness.
Quick Comparison
| Model | Best For | Material | Dropout / Rear Spacing | Item Weight | Amazon |
|---|---|---|---|---|---|
| Gravity FSX 26 inch Wheel Aluminum Disc Brake Full Dual Suspension Bike Frame★ Best Overall | Ebike and trail builds with full suspension | Aluminum | 135mm | 45 pounds | Amazon |
| Alta 20″ Bicycle Lowrider Bike Frame | Lowrider and custom cruiser builds | Alloy Steel | 32.5mm diameter | — | Amazon |
| Bicycle Gas Frame 3.4L w/o Kickstand, Fuel Tank Built in 3.4L Frame | Gas motorized bicycle builds with built-in fuel tank | Aluminum | 135mm | 4.67 kg | Amazon |
| NBPOWER Stealth Bomber Electric Bike Frame, Enduro | High-power 3000W–8000W electric builds | Alloy Steel | 150–155mm | 100 kg | Amazon |
In-Depth Reviews
1. Gravity FSX 26 inch Wheel Aluminum Disc Brake Full Dual Suspension Bike Frame with Rear Shock
Our pick — over 4.5★ from 30+ verified ratings; the strongest balance of quality and price.
The aluminum full-suspension frame that turns a box of 26-inch parts into a working ebike.
If you are converting an older 26-inch bike or starting an ebike build from scratch, this is the frame that lands the most praise from builders who post after the fact. The defining number is its 135mm rear spacing — that is the width of the rear axle slot, the measurement that decides whether your rear wheel and hub motor slot straight in. A standard rear hub or many hub motors drop right into 135mm, which is the size most aftermarket wheels are made to. The rear shock and seatpost clamp ship in the box, so you are not ordering them separately before your first bolt.
The frame feels solid, and the included fork, bottom bracket, and headset bearings save you buying them separately. Owners often open the box and are surprised to find a front fork, bottom bracket (the part that connects the pedals to the frame), and headset bearings (the bearings that let the handlebars turn smoothly) included with the frame. That means you can start building right away instead of hunting for separate pieces. A 185-pound rider says the stock suspension (the parts that soak up bumps) rides smooth with only minor sag (a little dip when you sit on it). Another rider put 550 miles on an ebike conversion and the frame held up perfectly. You can adjust the rear shock easily while you ride. Here’s a direct comparison: at 45 pounds, this frame is heavy next to the 4.67 kg CDHPOWER gas frame, but that weight gives you suspension travel (the up-and-down movement that absorbs bumps) and a sturdier feel once you add the motor.
The 15-inch size suits riders up to 5’6″, so taller builders should confirm proportions before ordering. One 5-star owner flagged that the seat tube inner diameter is 26.8mm, which is not a popular seatpost size, and the front fork takes disc or C brakes but not V brakes. On the electric side, the front disc brake mount is not compatible with ebike hub motors, so rear-hub or mid-drive setups fit this frame best. A separate owner reported a bend in one upper rear fork tube after use, an issue a builder can brace or leave for lighter, non-mountain riding. If you plan to push this frame hard off-road with high power, the takeaway is to inspect the rear triangle and support it if needed.
Where It Earns Its Keep
- 135mm rear spacing fits standard rear hubs and many hub motors without adapters.
- Rear shock and seatpost clamp arrive in the box, cutting your parts list before the first build day.
- Aluminum body holds up on electrified builds, with a 550-mile conversion reported as working perfectly.
- Heavy 45-pound frame rides sturdy with a motor attached and the suspension absorbs rough roads.
The Trade-Offs Up Front
- 26.8mm seat tube size is unusual, so pick your seatpost carefully.
- Front fork skips V brakes, and the front disc mount does not take ebike hub motors.
- 15-inch sizing tops out around 5’6″, limiting it for taller riders.
Grab these grips: the DIY ebike builder with 26-inch parts lying around who wants suspension, a rear shock, and a clamping headset in one order.
Measure twice: if you are past 5’6″ or running a front hub motor, check the numbers first so the fit is right.
2. Alta 20″ Bicycle Lowrider Bike Frame, Multiple Colors
A steel 20-inch lowrider blank canvas for builders who want to bolt on chrome and go.
Lowrider builders are a specific crowd, and this frame speaks to them directly. It is a 20-inch alloy steel frame made for a custom cruiser, with a head tube length of 102mm and a clamp size of 25.4mm. The 32.5mm inner diameter and the 32 3/4-inch frame length give you a compact, classic lowrider footprint. Everything about the size points to a bike you build for looks and neighborhood cruising, not for racing. Owners consistently describe the steel as nicely built and ready for chrome accessories.
Steel is the right material for this kind of build because you can prime, paint, and touch up the frame over time. Buyers who used it as a base for a project build say the tubing arrived straight and clean. One long-time rider captured the lowrider look: “Nice bicycle frame for a lowrider bike beautiful color.” The parts you add make the bike yours, so a clean, straight steel starting point is exactly what you want. If you plan a custom paint job, the black base gives you a neutral surface to work over.
The catch every lowrider builder should know is that this frame covers the skeleton only. There is no fork, bottom bracket, or rear shock, so budget for the chrome and the mechanical parts separately. That is normal for this category, but it means the frame is step one of a longer plan. It suits a patient builder with a clear vision, not someone who wants a complete bike in one purchase.
Straight from the box: the steel tubing arrives clean and ready for paint and chrome fittings, so the build starts on a solid base.
Plan a parts list: because the frame is the shell only, order your fork, cranks, and accessories as a set rather than frame-first.
The builder who knows their vision: 20-inch lowrider and cruiser projects draw the most from this steel frame.
Look past it if: you want suspension or a ready-to-ride bike, since this shell needs parts bought separately.
3. Bicycle Gas Frame 3.4L w/o Kickstand, Fuel Tank Built in 3.4L Frame – Gas Motorized Bicycle 66cc/80cc
The gas-bike frame that hides a 3.4-liter fuel tank inside the tubing itself.
For anyone building a motorized gas bicycle, the fuel tank is the annoying part that usually gets strapped on top. This frame solves that by building a 3.4-liter tank straight into the tubing, so the fuel disappears into the shape of the bike. It is aluminum and weighs just 4.67 kg, making it dramatically lighter than a heavy steel electric frame — you are carrying a fraction of that mass on a bike you pedal to start. The frame accommodates both 2-stroke and 4-stroke engines with a 135mm rear width, and it fits engines in the 66cc/80cc range this frame targets.
Buyers keep coming back for the welds and dropouts, which one 6’3″ rider reports arrived straight and square. One 6’3″ rider reports the welds and dropouts arrived straight and square and the frame fit a tall rider without issue. A separate build paired it with a YD100 78.5cc 2-stroke and reported the 3.4L tank is fine for normal riding, then added a 4L auxiliary tank for about 200 miles of range. The rear I.S. disc brake mounts are part of the frame. It even reached full-fueled builds at around 95 pounds with mag wheels, seat, and brakes attached.
Assembly detail is where you have to pay attention with this one. The bottom bracket uses a 68mm x 35.4mm sizing, the seatpost requirement is 27.2mm, and the headset needs 1 1/8 inches, so round up the right parts before you start. Builders with a quick-release rear wheel should be cautious, as the seller itself advises against buying this frame unless you are comfortable with mechanical work. Some buyers hit flattened cockpit or bottom crank threads and a factory finish that needed repainting. Notably, a handful of frames arrived with a dented handlebar neck that would not take a fork, so inspect the head tube area the moment it lands. The best safe racing speed listed is 35km/h, which keeps expectations grounded.
What Makes It Different
- 3.4-liter fuel tank is built into the frame, so no external tank to strap on.
- Only 4.67 kg, keeping a gas build light enough to pedal and start easily.
- Fits both 2-stroke and 4-stroke engines with a 135mm rear width.
- Rear I.S. disc brake mounts are built in, ready for your brake setup.
Where Your Wrench Comes In
- Some units have arrived with a dented handlebar neck that will not accept a fork, so check it on arrival.
- Threads on the crank and cockpit have needed re-tapping on a few builds.
- Not recommended if your rear wheel uses quick release unless you are mechanically confident.
Perfect for: a hands-on gas-bike builder who values a hidden 3.4L tank and can handle minor thread and finishing fixes.
Steer clear if: you want a plug-and-play frame or run a quick-release rear wheel and lack the tools to fettle it.
4. NBPOWER from USA Warehouse, Stealth Bomber Electric Bike Frame, Enduro Ebike Frame for 3000W/ 5000W/8000W Electric Bicycle DIY Kit
A steel Enduro frame built to survive 3000W to 8000W serial-q electric conversions.
When you bolt up a motor the size of a small scooter’s on a bicycle frame, the frame itself is the safety net. This NBPOWER Stealth Bomber frame is made from alloy steel with a high-strength plastic cover, and it is aimed squarely at 3000W to 5000W electric mountain bike conversions. The real strength is the adjustable dropout. Buyers report it uses interchangeable mounts for 135mm or 150mm, so you can match the frame to whichever hub motor you already own instead of buying around it. The rear shock takes a 190mm to 240mm shock, and the head tube is 1 1/8 inches non-integrated at 130mm in length. It ships from a USA warehouse.
As a working platform, it does the heavy lifting. The steel is thick enough that one owner recommends at least an 800 lb rear spring even for a light commuter build. Another converted an older bike to this frame and dropped in a 3000W motor with a 135mm dropout and 26-inch wheel, using just one washer to fit it. The metal tabs on the rear swing arm adjust the dropout width, so it can take a range of hub motors. Owners say the rear shock and fork soak up bumps that would rattle a rigid frame. There is also a real weight contrast worth knowing: at 100 kg, this frame towers over the 4.67 kg gas frame — steel this thick is the price of holding high power.
The honest caveats are worth stating plainly. This frame is heavy and long, which makes wheelies and tight maneuvers harder, and transporting it means a hitch adapter and a motorcycle carrier rather than a bike rack. One buyer notes the rear suspension hole needed slight filing where paint had built up. The moto seat option has to match the frame hole measurements, and it sits low and slides you forward, so pedaling becomes an afterthought. Order the right parts upfront, since this build rewards precision. If your plan is a commuter or light motor, the steel here is overkill — this frame is for serious motor power.
The build everyone talks about: the interchangeable 135mm and 150mm dropout takes the guesswork out of matching a hub motor, which is why owners keep flagging it as the standout feature.
Weigh the logistics: plan how you will carry and transport a frame this heavy before you commit to the build.
Built for the power hungry: 3000W to 8000W Enduro builds, heavy steel, and anybody chasing serious mountain torque.
Too much frame if: you want a light commuter, quick handling, or simple transport.
Understanding the Specs
Dropout spacing and rear width
This is the single number that decides what your rear wheel and hub motor can bolt onto. It is the slot width at the back of the frame where the axle sits. A 135mm spacing fits standard rear hubs and many hub motors, while 150mm or wider takes bigger motors built for higher power. Before buying, measure your own wheel or motor axle width and match it. Frames with adjustable dropout mounts are more forgiving, but the number still has to line up.
Seat tube and head tube sizing
These decide whether your seatpost and fork slide in without adapters. Seat tube inner diameter sets which seatpost fits; a common 27.2mm opens up big choices, while an odd 26.8mm narrows the field. The head tube is the front tube your fork steerer passes through and follows its own standard. A 1 1/8-inch head tube fits the most widely available forks, so you are not searching for a rare part. Check both numbers against the parts you own before ordering.
Frame material: aluminum vs steel
Material changes weight and how easily you can modify the frame. Aluminum tends to be lighter for its strength and resists rust, which suits moderate-power commuters and trail builds. Steel is heavier but can be welded, braced, and bent at home, which is why high-power electric conversions often use it. Both are valid choices; the power level and your willingness to modify the frame should drive the decision, not a brand name.
Suspension and brake mounts
Full suspension means the frame has both a front fork mount and a rear shock mount, and the rear shock may be included or sold separately. Whether your frame takes disc brakes, V brakes, or C brakes depends on its mount style, and that choice limits your brake options. Some front disc mounts will not accept an ebike hub motor, which points you toward a rear-hub or mid-drive setup. Confirm the mount style before you buy brakes.
FAQ
How do I know if a bike frame will fit my rear hub motor?
Can I put a gas engine on any of these frames?
What is the difference between 26.8mm and 27.2mm seat tubes?
Will the Gravity FSX frame work for a front hub motor build?
How much does the NBPOWER Stealth Bomber frame weigh?
Do I need to grease or prep the frame before assembly?
Which frame is best for a lowrider project?
What head tube size do I need for my fork?
Can I run disc brakes on the CDHPOWER gas frame?
Is a steel frame better than aluminum for an electric bike build?
Final Thoughts: The Verdict
For most builders, the best starting point is the Gravity FSX 26 inch Wheel Aluminum Full Suspension Bike Frame. It has 135mm rear spacing (the gap between the rear frame ends where the wheel fits) and comes with a rear shock and seatpost clamp. Owners mention it surviving ebike conversions, and the included rear shock and seatpost clamp cut your parts list. If you are building a gas bike and want the fuel tank hidden inside the frame, the CDHPOWER 3.4L Gas Frame is the one to get, with its built-in 3.4-liter tank and rear disc mounts (the brackets for rear disc brakes). And if you want serious motor power on an Enduro platform, the steel NBPOWER Stealth Bomber Frame with its interchangeable 135mm and 150mm dropout (the slots where the rear wheel axle sits) is built to take it. Whichever you choose, match the numbers to your parts before you order.
How We Picked
We do not accept paid placement. Every pick is matched to a real buyer and a real use-case; we do not hands-on test units.
Sources & Methodology
Specifications: manufacturer listings and product documentation. Review insights: verified customer reviews, as of September 2026. Pricing: not shown on this page (it changes often); check the current price via the retailer link.
As an Amazon Associate, Gadgets Feed earns from qualifying purchases. This does not affect which products we feature.