For women or men: Sporty touring bikes with a low step-through in the test

Many female cyclists get on their bike by lifting their right leg over the frame in front of the saddle. This works best if the frame has a low standover height and thus supports a low entry. The same applies, regardless of gender, to people whose mobility does not (or no longer) allow them to swing their right leg over the back of the saddle.

A spontaneous, naturally unrepresentative survey of the editorial team revealed that most women favoured the women's climb - some even practise this technique when climbing onto an MTB or road bike with a classic diamond design. The leg lift over the saddle, which "we men" use as intuitively as automatically, feels unfamiliar and even unsafe for many female cyclists. Most of them have never learnt it because, thanks to women's frames, they have never had to.

Unfortunately, a frame with a lowered step-through has design-related disadvantages: if it is not significantly heavier and more voluminous than a classic diamond frame, its riding dynamics deteriorate. The imbalance caused by pedalling manifests itself in counter-rotating, lateral pendulum movements between the saddle and handlebars, the frame twists under load - especially when pedalling harder or when a loaded pannier rack causes further disturbances in the balance system.

• CANYON PRECEDE:ON CF8 ST
• FLYER GOTOUR 5 7.23 D1 COMFORT
• KALKHOFF ENDEAVOUR 5.B ADVANCE
• BERGAMONT VITESS N8 BELT LADY
• CONTOURA AL 14
• ROSE BLACK LAVA 3 LADIES
• STEVENS 8X LITE TOUR LADY

These twists can impair riding stability and safety, as they tend to throw the front wheel off track. However, any loss of stability is undesirable at high speeds, with a child seat or a lot of luggage and even more so when riding one-handed or hands-free. In extreme cases, it can lead to a fall. The reason for the described stiffness deficits lies in the statics of the frame construction: The almost horizontal top tube of a diamond frame, which connects the upper ends of the head tube and seat tube, reliably supports lateral deflection. As a result, a "men's frame" only experiences disturbing lateral torsion under much higher forces.

Frames with a lower entry can never be as stiff as a diamond frame. Nevertheless, you can build excellent 'women's frames'. Riding fun and safety are not gender-dependent." - Jochen Donner, test editor

The force ratios are less favourable for frames with a lower step-through: several comparative measurements on "bike siblings", i.e. a men's and a women's bike of the same model, same design and frame size, showed differences in lateral stiffness of between around 12 and 20 percent between the two frame shapes, depending on the design and construction. The cross-sections, diameters and wall thicknesses of the frame tubes play a major role in frame stiffness. Generally speaking, the larger the tube diameter and the greater the wall thickness, the better the tube composite can withstand unwanted disruptive forces. The stiffer the frame, the safer the entire bike rides.

Strong e-bikes? Stiff enough on paper

With the e-bikes in the test, we didn't really expect the typical weaknesses of frames with a low step-through: pedelec frames are usually made of voluminous aluminium profiles, thick-walled and often angular in shape. Thanks to the motor support, the additional weight hardly plays a role. Intube batteries have intensified the trend towards tube volume. The measured values that we determined on our ECS test bench speak for themselves: all three pedelecs are at an unproblematic level of lateral stiffness. Canyon and Flyer easily top the values of even the best "organic bikes". So a lack of riding safety should no longer be a problem - or so we thought. But measured values are always a tricky thing: they are only meaningful if they correspond to the riding experience in practice. Test rides, especially with luggage, are therefore essential.

Flappy frames on some pedelecs

And on these test rides, a surprising realisation lurked: on the actually stiff pedelecs from Canyon and Kalkhoff, frame flutter occurs at the steering head when riding hands-free. The front wheel wobbles back and forth with increasing amplitude, the handlebar ends swing and the front frame sways. If you put both hands on the handlebars, the situation quickly calms down. This happens in the speed range of around 17 to 25 kilometres per hour, with a luggage load correspondingly earlier and with more energy.

This fluttering of the handlebars or frame is obviously due to the fact that the down tubes, which are cut open to accommodate the Intube battery and are a type of U-profile, are surprisingly poor at resisting longitudinal twisting above a certain natural frequency. During the test rides, a clear twisting could be observed at the joints between the battery and the down tube. The batteries themselves cannot and must not have a stiffening effect, as they are not designed as a load-bearing structure for reasons of stability and safety.

When and how much frame flutter occurs also depends on which and how many stimulators are in play. The Flyer, on the other hand, remained completely stable: the battery sits transversely behind the seat tube. The four "non-electric" ladies' bikes also rode without any rocking.

The frames of these bikes consist exclusively of more or less round tubes. They proved to be less sensitive to torsion than the open profiles with battery mounts. The cross-mixed frame of the Contoura demonstrates outstanding riding stability among the muscle-powered bikes: in terms of handling, the AL 14 is not far removed from an agile, racy racing bike. Even the bikes from Rose and Stevens could not be thrown off course by touring luggage or hearty pedalling. Even the Bergamont, with its relatively low stiffness measurement, remains easy to control when used sensibly.

A tendency can be recognised: The more weight is concentrated on the motor, battery, cockpit or loaded pannier rack and the further apart these compact masses are on a bike, the more intensely they act as disturbing impulses - and the more unsteady the riding behaviour becomes. If handlebar flutter occurs unexpectedly and at high speed, it can be dangerous. Flutter effects cannot be completely avoided, they are due to the design. It is important to be aware of this - and in the worst case, to calmly slow down.

How we test: Measurement of frame stiffness in the laboratory

On our pneumatically operated ECS test stand ("E-Bike Centre Stiffness", Zedler-Institut, www.zedler.de), the test bikes are fixed to the dropouts of the fork and frame ready to ride, but without wheels. Using form-fit adapters, the test stand grips both ends of the crank axle and pulls the bottom bracket area to the side with a defined force, alternately to the right and left from the centre axle. The deflection achieved, sometimes several centimetres, is measured and recorded. The measured values in Newtons per millimetre (N/mm) provide information on how laterally stiff the respective frame-fork system is. We currently rate values from 80 N/mm with a sub-rating of 1 in the riding safety category. Below this, the rating drops one grade every 5 newtons. Handlebars, stem, saddle, seat post and especially the pannier rack cannot be included in the measurement. Therefore, the final evaluation of the test bike is always closely linked to the personal riding impression gained from intensive test rides with and without luggage.

Interview with Dipl.-Ing. Dirk Zedler

Publicly appointed and sworn expert for bicycles and electric bicycles

MYBIKE: What are the pitfalls of a frame with a low step-through compared to a diamond frame?

Similar to a truss, the centuries-old principle is a stroke of luck: every frame tube that is omitted reduces the riding stability. On a step-through bike, the front part of the frame can move more easily than the rear. Designers have to think a lot more about stiffness and durability.

Are there differences between classic bikes and pedelecs?

Pedelecs have heavier components, the riders take more luggage with them, and the drive allows more users to tackle hilly terrain, including fast downhill rides. Pedelec users also like to sit upright. The requirements for pedelecs are therefore significantly higher. This is why a rack-mounted battery is extremely questionable. If, on the other hand, the battery is located on the outside of the centre or down tube, behind or in front of the seat tube, the pedelec rides much better.

What is the relationship between frame stiffness and steering head wobble?

You can see this with the Intube batteries on step-through bikes: some manufacturers simply cut open the tube to integrate the battery. The down tube then offers hardly any torsional resistance. Even if everything else fits, the suspension becomes unstable even at low speeds. Handlebar flutter as a phenomenon, but also the dangerous riding instability downhill, for example when changing direction, are not only unsettling, but also lead to accidents.

When buying a bike, how can I be sure that the bike I want with a low step-through offers sufficient riding safety?

The method of "looking closely" is not enough. MYBIKE tests, on the other hand, in which the riding stability is measured and categorised during test rides, are. In addition, I can only advise a detailed test ride with an adjusted seating position and definitely with luggage. The latter in particular separates the wheat from the chaff.

You can download the complete comparison test of the women's bikes from MYBIKE 3/2021 including all individual ratings as a PDF below the article.

Downloads:

Test women's bikes with and without motor (pdf)