Minimizing Step-through Frame Flex

Dewey

Well-Known Member
that would be easy to get on but can you imagine riding that 50 miles or climbing 20% grades on?
Not 20% grades, but a front hub conversion like this should be quite comfortable on milder hills, I’d talk to Grin Tech in Vancouver who are great at specialist conversions.
 
  • Like
Reactions: JRA

Handlebars

Well-Known Member
Region
Canada
As indianajo said, it is not the frame flex but heavy load on the rear rack. I have been carrying heavy groceries on rear racks of all bikes and e-bikes I used to own for a long time, and the erratic behaviour of the rear wheel is a norm, regardless of the frame type. I weigh 200 lbs, and experience the bike rear wobble with the superlighweight, diamond frame Vado SL just because it is a lightweight, narrow tire e-bike. If I ride my heavier, step-through Vado, the phenomenon is far less pronounced.
The bike that flipped right over had no noticeable wobble. What it had a was a nice rear rack that extended back further than what I figure it should have had. All it took was going over a little sidewalk on-ramp on a hill slope. Actually flipped it another time before I fixed it, so I'm sure of what caused it.
 
Last edited:

fooferdoggie

Well-Known Member
Not 20% grades, but a front hub conversion like this should be quite comfortable on milder hills, I’d talk to Grin Tech in Vancouver who are great at specialist conversions.
I would not want a front hub on a tandem the front slips too easily as it is. we have to be so careful on hard packed trails as is. we have done 3000 feet in 40 mile rides with lots of 15% or more grades.
 

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
I would say have your BF look into welding on twin mixtie top tube bars. These could on your bike extend from the seat stays to the steer tube, with a couple of cross members. The front of the rack could also have twin bars that connect to the seat tube at the seat stays. Most racks do.
1640638191830.png
1640638431361.jpeg
1640638605092.jpeg
 

frostcrystal

New Member
Region
USA
As indianajo said, it is not the frame flex but heavy load on the rear rack. I have been carrying heavy groceries on rear racks of all bikes and e-bikes I used to own for a long time, and the erratic behaviour of the rear wheel is a norm, regardless of the frame type. I weigh 200 lbs, and experience the bike rear wobble with the superlighweight, diamond frame Vado SL just because it is a lightweight, narrow tire e-bike. If I ride my heavier, step-through Vado, the phenomenon is far less pronounced.

It was the front wheel that I lost control on. It was sort of swaying side to side like a speed wobble, or that swerving you get when you're going much too slow, except I was going at about 11mph. I managed to get home by really clamping down on it with stiff arms. It sounds as though my path forward is to attempt to balance out the load more toward the front somehow?

That said, I've definitely hauled some heavy loads on my regular (step-over, non-powered) bike with no issues, which was why I jumped to the conclusion that it was the step-through that was the problem with this bike.

Is there any chance this bike needs to be running a little more air in the tires? If they were low, it would seem to me like they would allow/encourage some flex/sway/bad handling, especially when heavily loaded.
It's a possibility. I'm usually quite good about making sure the tires are inflated, but I also don't usually inflate them to the fullest extent.

Thankfully I'm a girl so I can ride step-through bikes without worrying about my image, hahaha. They ARE nice and easy to mount, even if I'm more comfortable with the top tube.
 
Last edited:

frostcrystal

New Member
Region
USA
I would say have your BF look into welding on twin mixtie top tube bars. These could on your bike extend from the seat stays to the steer tube, with a couple of cross members. The front of the rack could also have twin bars that connect to the seat tube at the seat stays. Most racks do.
View attachment 110352View attachment 110353View attachment 110354

I've never seen those before! What is the advantage vs attaching directly to the seat tube? I think the issue that he mentioned with this bike is that there isn't much room above the battery on the steer tube to add a top tube; it's doable but it'll be tight.

It was also suggested to me elsewhere to add the stays to the rack. It currently attaches (weirdly enough) to the fender, but I think it's also welded directly to the frame at the bottom. I'll definitely look into it.
 

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
I've never seen those before! What is the advantage vs attaching directly to the seat tube? I think the issue that he mentioned with this bike is that there isn't much room above the battery on the steer tube to add a top tube; it's doable but it'll be tight.

It was also suggested to me elsewhere to add the stays to the rack. It currently attaches (weirdly enough) to the fender, but I think it's also welded directly to the frame at the bottom. I'll definitely look into it.
What appears to be the sway at the front is in fact caused by flex at the rear. Steering is caused by the rider fist leaning in the opposite direction of a turn. You are naturally compensating for the noodle effect causing what feels like steer wobbles up front. The front is not the cause. It is a symptom.

Another thing to note: Aluminum does not like to flex. Springs are not made of it. When it flexes it develops fatigue fractures.
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Mazovia, Poland
It was the front wheel that I lost control on. It was sort of swaying side to side like a speed wobble, or that swerving you get when you're going much too slow, except I was going at about 11mph. I managed to get home by really clamping down on it with stiff arms. It sounds as though my path forward is to attempt to balance out the load more toward the front somehow?
Your e-bike is equipped with a hub-drive motor, adding to the rear weight. Additionally, your e-bike is designed for riding in the upright position. It just means the front is not loaded enough. I cannot find the cure for that but that's decidedly not the frame flex.
 

indianajo

Well-Known Member
Rack welded to the fender is definite sleaze. A fender has no strength. When my MTB had rim brakes, the frame was wide enough at the top, I put clamps around the two struts. 2 1/2" apart. Then I ran 6" long 5/16"NC bolts to the frame of the baskets splayed out to the side. Angle brackets were bolted to the basket frame. Then I could tension the basket towards the front of the frame. It limited the sway, but not enough. The rack welded to the frame of my bodaboda is much more stable from side to side.
 

Solarcabin

Well-Known Member
Region
USA
Does anyone have suggestions for minimizing frame flex? My fiancé is in the machinery/engineering sphere and has suggested making an attachable padded 'top tube' that could be screwed on, but that is all I've got. It would be cool to hear from someone who has done something similar or dealt with similar issues.

Retrospec Bike Rack Cross-Bar Top Tube Adjustable Adapter​

 

Attachments

  • sway stopper.PNG
    sway stopper.PNG
    42.4 KB · Views: 57

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
If not the frame, fine. Maybe not. This problem arises when the back wheel is out of true or there are loose spokes. Easy enough to check. On second thought I will put my money on it. Have BF flip the bike, feel the spoke tension and look for a broken spoke or lack of true.
 

frostcrystal

New Member
Region
USA
If not the frame, fine. Maybe not. This problem arises when the back wheel is out of true or there are loose spokes. Easy enough to check. On second thought I will put my money on it. Have BF flip the bike, feel the spoke tension and look for a broken spoke or lack of true.

Tragically you'll lose money on that haha. I took the bike to a LBS shortly after buying to make sure everything was good (habit of mine from Goodwill bike sales). No loose spokes, both wheels in true. Was thrown a month or two after and it was one of the first things I checked after that.

EDIT: I have lied to you all, the bike rack is not welded on at the bottom. Bafflingly, the seat stays have bolts for rack brackets, but the rack itself doesn't, so I'm not sure how I would attach brackets to it. I guess I could take a drill to it.

1640648810998.png
 
Last edited:

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
Tragically you'll lose money on that haha. I took the bike to a LBS shortly after buying to make sure everything was good (habit of mine from Goodwill bike sales). No loose spokes, both wheels in true. Was thrown a month or two after and it was one of the first things I checked after that.

EDIT: I have lied to you all, the bike rack is not welded on at the bottom. Bafflingly, the seat stays have bolts for rack brackets, but the rack itself doesn't, so I'm not sure how I would attach brackets to it. I guess I could take a drill to it.

View attachment 110373
Or. something like VersaMounts could work, to support the rack but you would need large shims. Better than drilling.
 

Kayakguy

Well-Known Member
I have an Ariel Rider C class, which is a step through. It has a built in (or on?) rear rack, to which I've added a top trunk and folding baskets on each side. The top trunk never carries much weight. I regularly load the folding baskets up with groceries which can be pretty heavy--beer, milk, etc. Often, the extra weight is all on one side, and I never notice any problem whatsoever from that. I have never noticed any sway or wobble that seemed to result from the step through configuration. In fact, there's not much movement at all in the frame. The battery is on the front of the seat tube, making the frame resemble one of Rad's bikes (don't know the model name). That puts the weight low and centered. Also has a mid motor. I do carry a bag on the handlebars, but it doesn't carry much weight. I have never had the front wheel threaten to lift, even though this is a very short wheelbase bike with an upright riding position (which I really like, as my wrists and hands used to get painfully numb after some distance).

I like the step through because on my former non-electric Trek diamond frame, swinging my leg over with the rear rack loaded was extremely awkward. Whenever a sassy kid says, "Hey boomer, how come ya riding a girl's bike?" I answer, "This ain't no girl's bike kid, this here's a STEP THROUGH! Besides, I'm too old to qualify as a boomer."
 

Kayakguy

Well-Known Member

Retrospec Bike Rack Cross-Bar Top Tube Adjustable Adapter​

My wife and I both pedal step-thrus (only mine is an ebike). To transport these on a platform rack, we needed to equip both bikes with that type of removable top tube. Worked great for our purposes, but I can't see it doing anything for frame stiffness, as it isn't attached solidly at either end.

My ebike is an Ariel Rider C class. I have a small trunk on the rear, and folding wire baskets as panniers. I use it often for grocery shopping, and have never noticed frame flex. I may not be loading cargo as heavy as you are carrying, though.
 

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
A frame adaptor is only for hanging a step through on a rack. They have nothing to do with the structural rigidity of a frame. I have only experienced a noodle-like twisting flex in a steel Mixite. If your frame has flex like this, use a different frame. This bike is nice. It feels like a Como. Note the lack of ugly wires. It is a mid-drive. I started with a Giant Momentum Vida frame. The ride is smooth. The red one had that wet noodle twisting flex. Part of the problem was the older style, heavy battery.
1648586847745.jpeg
 

Attachments

  • Vida2.JPG
    Vida2.JPG
    425.4 KB · Views: 36
  • Vida3.JPG
    Vida3.JPG
    373.7 KB · Views: 34
  • DSCF7260 (2).jpg
    DSCF7260 (2).jpg
    803.5 KB · Views: 32