Most people considering a step-through e-bike have the same two questions before buying. Does a frame without a top tube offer the same stability as a classic diamond frame, and is the bike just as safe at higher speeds?
A modern step-through frame is usually just as strong as a diamond frame, and in everyday riding it is even calmer. This article explains in detail how a frame without a top tube works and which figures in the spec sheet deserve special attention. The Dukawey FUGL 3.0 serves as the example.
How a Step-Through Frame Compensates for the Missing Top Tube
One Large Down Tube Instead of Two Thin Tubes
Basically, a tube becomes disproportionately stiffer against bending and torsion the larger its diameter is. This is an important principle in engineering. Doubling the diameter makes the stiffness roughly eight times greater. That is why modern step-through e-bikes have a noticeably large down tube, usually with an oval cross-section.
On the FUGL 3.0 the down tube does two jobs at once. It carries the standard frame loads and additionally houses the 672 Wh battery. This is supported by a reinforced junction at the head tube, where steering forces act, and by the rear triangle, which remains a closed triangle.
Is a Step-Through Frame Really Wobblier?
Whether an e-bike tracks calmly in a straight line and feels safe at higher speeds is decided mainly by geometry and centre of gravity; the frame shape plays only a minor role. Because the battery sits in the down tube of a step-through frame, the centre of gravity is low, close to the ground. Thanks to this combination, the bike stays composed in corners and in crosswinds.
The rest of the geometry also helps to calm the ride. With a wheelbase of 1,150 mm, the wheels of the FUGL 3.0 are roughly as far apart as those of a trekking bike. The longer this distance is, the less small steering inputs and potholes knock the bike off line.
The 71-degree steering angle also calms the steering. Much like a shopping trolley castor, it makes the front wheel trail slightly behind the steering axis, which straightens the steering by itself at higher speeds. All of this results in straight-line tracking that is relaxed and predictable at 25 km/h. It requires a little more steering input in tight corners, but in city traffic that is rather pleasant.
With a well-designed frame, you therefore notice no significant difference compared with a diamond frame in normal riding. A heavier rider may occasionally feel slight flex when riding out of the saddle uphill with a fully loaded rack, but the frame compensates for it immediately.
On an e-bike this situation is rare, though, because the motor makes riding out of the saddle unnecessary. With a rear motor delivering 65 Nm, the FUGL 3.0 does the work for you while you simply stay seated instead of standing on the pedals.
Does a Step-Through Frame Feel Heavier to Ride?
While riding, the motor offsets the 29.5 kg of the FUGL 3.0, and the upright riding position is easy on the back and wrists over longer distances. You therefore notice little of the weight or the frame shape on the move, but the low step-through pays off when you stop.
At a traffic light or in your driveway, you take a small step forward and stand with both feet flat on the ground, without swinging a leg over the saddle or the rack. The FUGL 3.0 has a stand-over height of 42 cm. A diamond frame, by contrast, sits at around 75 to 80 cm. That is exactly the difference that turns an almost acrobatic dismount into a simple lifting of the leg.
With shopping on the rack or a child in a child seat, the bike can quickly weigh over 40 kg. A secure footing matters most in exactly those moments, making a fully loaded bike noticeably easier to balance.
Maximum Load of a Step-Through Frame
The Testing Is the Same for Every Frame Shape
Every e-bike sold in the EU must meet the requirements of the EN 15194 standard. The standard does not distinguish between frame shapes, which is why a step-through frame has to pass the same tests as a diamond frame.
Total Weight and Payload
For the FUGL 3.0, Dukawey specifies a maximum load of 180 kg. Subtracting the bike weight of 29.5 kg leaves around 150 kg for rider and luggage. According to the spec sheet, the rear rack is rated for 50 kg. That leaves plenty of reserves for full panniers and other cargo.
| Value | Dukawey FUGL 3.0 (step-through) | Typical city e-bike |
|---|---|---|
| Maximum load per spec sheet | 180 kg | 120 to 150 kg |
| Bike weight with battery | 29.5 kg | 23 to 28 kg |
| Rear rack | 50 kg | 25 to 27 kg |
| Frame material | 6061 aluminium | 6061 aluminium |
| Tyre width | 2.5 inches | 1.75 to 2.0 inches |
What to Look for Regarding Stability When Buying
With a reputable manufacturer you do not necessarily need to question the frame shape itself; the following figures in the spec sheet matter more.
Load capacity
Add up your weight, your luggage and the bike weight, and allow yourself a 10 to 15 kg reserve. The FUGL 3.0 is specified at 180 kg, which is enough for practically any rider with luggage.
For a child seat, the rack should be rated for at least 25 kg. The 50 kg of the FUGL 3.0 is a very strong figure in this class.
Geometry
Look for a wheelbase of over 1,100 mm and wheels sized 26 to 28 inches if you want a calm ride even at higher speeds. 20-inch folding bikes are more agile and compact, but they demand a little more attention at 25 km/h. Anyone who rides a lot on open roads is better served with larger wheels. Also check the recommended rider height in the spec sheet so that the saddle and handlebar fall within your adjustment range.
Tyres and brakes
Wide tyres from 2 inches carry more air volume, absorb cobblestones and protect rims and spokes under heavy loads. The FUGL 3.0 runs on 2.5-inch tyres.
The higher the total weight, the more important braking performance becomes. Hydraulic disc brakes like those on the FUGL 3.0 brake with less hand force and are easier to modulate than mechanical ones.
Conclusion: Stable Enough for Almost Any Use
The concern about stability dates back to a time when step-through frames had thin steel tubes and were designed for leisurely rides. A modern aluminium step-through frame with a large down tube, integrated battery and tested design to EN 15194 plays in the same league as any diamond frame. The FUGL 3.0 proves this with a 180 kg load capacity, 50 kg on the rack and a 1,150 mm wheelbase.
How capable this step-through frame really is in everyday use has also been analysed in detail by the independent site E-Bike-Ratgeber.de. Its review of the Dukawey FUGL 3.0 puts the stability figures into context within the overall package and awards 4.3 out of 5 stars.
Frequently Asked Questions
Is a step-through e-bike less stable than one with a diamond frame?
No. The missing top tube is compensated for by a significantly larger down tube, and the rear triangle stays closed anyway. Both frame shapes have to pass the same EN 15194 tests.
How much weight can a step-through e-bike carry?
It is listed in the spec sheet as the permissible total weight or maximum load. City e-bikes are usually between 120 and 150 kg. The Dukawey FUGL 3.0 specifies 180 kg, and the rear rack is rated for 50 kg.
Does a step-through frame wobble at high speed?
Riding stability depends mainly on geometry and centre of gravity. A long wheelbase like the 1,150 mm of the FUGL 3.0 and the battery sitting low in the frame keep the bike tracking calmly at 25 km/h.
Can I fit a child seat on a step-through frame?
Yes, as long as the rack is rated for it. Most rack-mounted child seats require a rack load capacity of at least 25 to 27 kg. With 50 kg on the FUGL 3.0, that requirement is met. The total weight of bike, rider and child must stay below the load limit.
Why are step-through e-bikes heavier than others?
The large down tube, the battery integrated into it and the components designed for high loads all add weight. The FUGL 3.0 weighs 29.5 kg with the battery and around 25 kg without it. While riding, the motor makes up for it.
Does a step-through frame ride differently from a normal e-bike?
Yes, calmer and more upright. Thanks to the low centre of gravity and the longer geometry, the bike tracks very steadily in a straight line.