Is the frame type (diamond, step-trough) still relevant for stability

[Skelshy]

I'm on the heavy side, plus I often have a kid seat mounted on the bike which makes it much harder to swing a leg over the bike to get on it. I was wondering if a diamond frame is still needed for stability (it used to be step-through bikes were all wobbly)? If no, I would just have an easier time getting on and off the bike in the city with a kid with a step-through design.

Opinions?

Thanks

 

[indianajo]

I'm carrying 170 lb me and up to 80 lb supplies on the step through frame left. I bought that one because it is special for short people. My pants inseam should be 28". It is a yubabikes.com .
No wobbles. This is not a racer, weighed 63 lb as delivered and rides about 75 now with full set of tools, tubes, bags, battery, motor.
Other stretch cargo bikes, xtracycle, surlybikes (steel frames high capacity), pedego stretch, radwagon, blix packa, the original kona ute, tern GSD (20" wheels) . these put the rider's weight on the front wheel and leave more of the rear tire for the cargo. Many have special features to interface with certain brands of child seat. Mine has spoke shields standard to keep the child's fingers from being pinched. Look into the double leg frame, makes loading much easier.
See this topic about cargo bikes, which usually have a weight rating. https://electricbikereview.com/forums/forum/cargo/
I've converted my pedal bike with a front drive geared hubmotor $221 and $620 for a 17.5 ah battery that doesn't have a patented shape or connector. So I can buy any generic battery in 4-6 years when this one wears out. Likewise if the motor craters, a new one is about $250 with drive, throttle, PAS, brake handles.
The yuba was perfect when I got it, needed no spoke torque checking monthly that rad specifies, and I got 5000 miles out of the 8 speed chain since the motor doesn't drive through it. Sprokets no wear yet. The front drive is not a problem, plenty of traction. I don't ride on black ice. I do ride year round, don't run a car anymore. do all my shopping off the bike.
See you are in Germany. Reise & mueller sells an expensive & respected cargo model both in Europe & the US. Bosch mid drive wears out chains more like 1000 miles, and pedals without power like dragging an anchor. I've ridden mine home 25 miles unpowered when a heavy rain disabled the throttle. I ride unpowered 90% of the time, reserving motor for headwinds >12 mph, trips over 25 miles, and crossing 6 lane streets on 6 second green lights with the throttle to the max.

 

[TMH]

While full diamond will likely continue to be the most solid/rigid, I believe that in general the improvements in frame design and materials (especially things like hydroformed tubes which allow more structural rigidity when required) make many of today's step-thru's less flexy than previous generations.

Different bikes also are designed for different overall weight carrying capacities. The ones with the highest carrying capacity, if choosing between step thru's by different manufacturers or even just different models from the same manufacturer, will generally be the stiffest.

Different designs choices will also improve rigidity. For example, when I have ridden my wife's Ride1Up step thru, I can definitely feel frame flex. It's frame looks like this, with an extremely low step over height:

However a design like Specialized chose for the Turbo Vado/Como uses an extra bar which results in a higher (but likely still very comfortable) step over height, but much less frame flex:

 

[Katysax]

I ride a low step Specialized Como. The ride is extremely solid. No flex.

 

[Stefan Mikes]

The modern step-through frames made of hydroformed aluminium are very stable, especially with the top tube adding to the structural stability. I was 107 kg (236 lbs) when I first started riding e-bikes, no issue with the stability. Many manufacturers offer lifetime warranty on the frame, meaning they are sure their frames are durable.

 

[Dewey]

Frame flex or speed wobble is still an issue on some ebikes, Court's video reviews sometimes demonstrate this, for example on the Pedego City Commuter step-through here

But as others have pointed out it varies between different designs so test ride before you buy.

 

[steve marino]

That Honda Super Cub is drop dead gorgeous. Much nicer than anything being made today or in the last 30 years. Personally, I've never heard of a step thru frame exhibiting wobble or instability on a bike or a motorcycle. Maybe it happens, but in over half a century of riding both, no one I knew of had a lick of trouble w/ this.

 

[steve marino]

Well, it's a rare day when I know what I'm talking about, but I've learned to fake it pretty well. Like my ex wife used to say, if you can't dazzle 'em w/ brilliance, baffle 'em with BS.