Frame failure investigation..

so about a year ago, my custom steel frame broke around the chainstay over here



this was a columbus steel frame with supported several mid-drives around 1500-2000 watts, it rode for 2 years around 10000 km
while there might several reasons to this (one being there were times i didn't tighten enough the sliding drop outs, the wheel would skew and rub against the chainstay without me noticing it) i think i cam up with another cause. which i'm thinking over when trying to design a new frame from my builder.

this is the bare frame


and this is how it looked when fully loaded


the seat angle was 71 degrees, and most of the time it sported a cane creek


which also broke.


when i ordered the frame i wanted to sitting position to be upright with a large triangle to house a battery.
the problem was the angle seat tube didn't go well with the b190 saddle, which pressed on .. ah... sensitive area, when i tried to reach the handle bars.
so most of the time i would be try to move back as possible on saddle to avoid that area...
now if you consider i was 250 lbs (230 now) , when i look the photo of the frame fully loaded i think this created a huge load on the frame , especially when i would hit a speed bump on the road, brake, or drop from a large pavement (i won't lie it was rather fun feeling the springiness of the seat along with the crane creek absorbing the shock) .

but since frame had no jig around brake side like some frames do, and because of the combination of my sitting arrangment and angle, those could have contributed to the frame failure right?

because i wanted a 29er with 68mm threaded bb shell, i've ordered this frame (venzo frame, heard it had some good reviews, but you can pick it at wal-mart which doesn't sound good) , which has 73 degrees seat angle as test before i try another custom fame, you'll notice it's chainstay are shaped more robust and do have support on brake side. while it's only 20" (i'm 6'3), i have a 20" paratrooper pro which feels rather nice.



what do you think? could i be right?

You built the opposite of a longtail, moving your ass weight further back with the thudbuster. Then you loaded it like it was a longtail.

Your next frame needs to be a steel longtail cargo bike. Period.

I doubt riding it loose helped any, but you seriously loaded the rear end. This pounded the rear of the bike, having it need to bounce your ass up every bump. A longtail will ride like a teeter totter, so the rear weight can rock up and down though the bumps, without having to lift your ass too.

Seriously, longtail, or rear suspension is what you need.

You already bought it, and maybe it will last longer than the last one. But to eliminate the potential of a repeat, you can't just do the same thing again. So look into the possibility of building a dropout plate torque arm, than also lengthens the bike 4" or so.

are you saying i needed a long tail only because how far i've reached ?

that will no longer be the case, having my seat in 71 degrees this far back made the brooks sitting angle very uncomfortable. which what forced my to go back even further.

the new frame will have 73 degrees seat tube angle and will shorten the reach from to the handle bars, the seatpost itself will be straight
(like it is now with paratrooper pro below) i actually ordered the new frame partly for measurements to see how it would feel like.
so my aim is actually moving everything to the center not back,(after all that's one of the reasons why i wanted to have the triangle battery and mid-drive to keep the weight centered not back, i just didn't realize the side effects that would happen with brooks saddle)

my builder suggested using a tandem chainstay. folks seem to agree, it's just i need to think on the geometry
as for the load, if you're referring on rack and back pack. those usually contain just the charger and a towerl, i use them mainly for shopping, nothing else


full suspension frame, sounds nice, but sadly, there are no fs frames with 68 mm bb shells, basically all my mid-drives brackets (my gng modified gng 2015, ecospeed ,l-r) are all 68 adapted, i even contemplated on trying to reverse engineer the gng brackets to and use my openbuilds cnc router to make new ones, however considering the learning curve involved (need to actually draw the brackets, 3d print them, prototype, learn how to use openbuilds etc..) seemed way too long, i'm a little more pressured because i'm using bbshd , i've passed 1000 km (although my usage is rather tame, usually 30-35 km, around 1000w) i'm still afraid of opening it.

You have so much crap attached to that bike, it's clearly beyond its design intent. But the dropouts are also not very well designed to handle braking force. And there may have been an unnecessary stress riser at the plug style dropout, or an excessively heat-affected zone, or both.

Don't expect to take a sporting bicycle and press it into use as a truck without having to deal with the consequences. Either use a bike that's built for the job (as Dan suggests), or else add a trailer for your pile of stuff. I recommend the Yuba Mundo bike or Extrawheel trailer for the amount of burden you show in your picture.

define "so much crap",

for the electrical i have a mid-drive, 12 fet infinion controller and a 24.5ah 52 em3ev triangle battery,

other then those i have:

rear bag that contains a bike cover, charger and a towel.
the bag under the saddle contains tire liner and inflation kit.
the front bag on the handle bar a set of tools (wrenches, allen keys) .
the front side bags basically contain rubber gloves, and usb cables for charging.

so yea a lot of bags, but not a lot of or heavy content (further more the bags themselves are actually used to masquerade that it's electrical, people often only see it's true nature up close in elevators going "wait, is that a motor?") this is why i have a "sweat" cover across the toptube to hide the wires.

that's basically it.. do i really need a trailer that's able to carry 2 kids just for those things? it's not for touring, i don't carry things like
tent, hiking equipment and so on, none of that.
these are more or less the same things i would carry (and have carried) on a normal bike as well. i don't get it.

what dropouts would you recommend?

Dead weight counts for more than equivalent rider weight. Weight on the top of the rack counts more than the same amount in a pannier. Weight cantilevered from the bike's structure is more punishing than weight that sits directly on it.

There are lots of bikes designed to carry as much luggage as you have or more, but your bike isn't one of them.

An Extrawheel trailer doesn't carry even one kid, tracks narrower than your bike does, and weighs less than 5kg even with a sturdy wheel. It's only designed to carry a pair of panniers. That's why it's a better match to your bike as you have configured it.

Where the break was located I would have been tempted to take all the electric stuff, racks and gear off and get your framebuilder to turn the fracture into a splitter for a belt drive system he he.

Is it possible to repair the frame by replacing the broken stay with a "beefed-up" one or reinforcing the broken one? Also, the Venzo frame is aluminum AFAICT; doubt it will fare better than the steel frame.

the frame was already repaid with welding and after a year i've noticed a crack forming next to the weld, i took to a welder again but he worked on it for 20 minutes but even though he repaired it, he said it was too risky.


Yuba mundo bike is shown to carry 2 kids, that's what i meant, but a trailer is an overkill, so i'm guessing the alternative is not have a rack and bag at all? or maybe a bag with a rack that attaches to the seattube?

i know the venzo is aluminium, i wanted to order it mainly to get a feel for measurements for the custom frame.

Yikes.
You want a Yuba, or something like it. It's a frame that's rated for over 400lbs.

Also, you've got what looks like too small of a frame for your body size, indicated by how tall you have the seatpost! And the front end geometry is not right at all. I can tell because the angle of the seat post and fork is very extremely raked backwards. This is due to your front fork, which looks like it's >50mm taller than the bike was designed for.

..and these geometry issues cause the rear to be loaded way more than it was designed for. And of course then, you had to throw a rear bag on.. with how many pounds in it? geez.

Also, the long travel cane creek seatposts are known for not being reliable. They break in various ways. The short travel version is much more reliable though.

Shift more of your weight up front with a correct size frame for your body and you'll need all that ass cushioning a lot less.

neptronix said:

Yikes.
You want a Yuba, or something like it. It's a frame that's rated for over 400lbs.

Also, you've got what looks like too small of a frame for your body size, indicated by how tall you have the seatpost! And the front end geometry is not right at all. I can tell because the angle of the seat post and fork is very extremely raked backwards. This is due to your front fork, which looks like it's >50mm taller than the bike was designed for.

..and these geometry issues cause the rear to be loaded way more than it was designed for. And of course then, you had to throw a rear bag on.. with how many pounds in it? geez.

Also, the long travel cane creek seatposts are known for not being reliable. They break in various ways. The short travel version is much more reliable though.

Shift more of your weight up front with a correct size frame for your body and you'll need all that ass cushioning a lot less.

Click to expand...

no, i don't want a frame rated 400lbs because i have no intention of loading 400lbs on it, as i've said in post above, the back contains usually nothing then a charger, bike cover and a towel. that's it, side panniers usually contain nothing other then groceries, i have no intention of loading this bike (aside from the mid-drive and triangle battery) anymore then i would a normal bike.

i'm 6'3 and 230 lbs, down below is the geometry my frame builder used, that's a custom frame, and he added the front fork.
the original intention was to have an "upright" riding position, rather then being leaned forward like a road bike which would cause shoulder pain. and i also agree, it turned out to be way more back then i anticipated, causing problems with sitting again, which is why i'm planning to shift a lot more forward.

the bike seem to have lot of bags, but they aren't used for touring. if that means i can never have a rear bag with normal bike with a mid-drive?

Okay, so the the rear bag is not loaded, which is good.. but 230lbs of you is upright and leaned way back, which is creating the rear stress on the rear. The angle of the seat post is another concern..

And you should have what we call an extra large frame if you're 6 foot tall, but you're riding what looks like a medium from here.

If you have shoulder pain when leaning forward on a roadbike, you need to work on your upper body strength AND your posture. I would bet that your biomechanics are off from a lifetime of sitting at desks and using things designed for much shorter people causes you to hunch forward and thus your muscles and cartilage wear pattern are way off balance. I'm 6 foot tall but with long limbs and had this problem too until i started paying attention to it and began correcting it.. now i can handle a road bike ( after 4 years of correcting my forward hunch ), which balances more of your weight forward.. and improves aerodynamics massively

Nonetheless if you want to continue putting a majority of your body weight on the rear, you're going to need a frame designed with that in mind. One that is rated for over 300lbs will be necessary.

However, finding a suspension seat post will always be your problem if you continue to rely on messed up geometry. If you had a bike frame that's appropriate for your size ( IE, handlebars forward by 24-50mm, and seat tube just barely sticking out of the frame ), these problems with things being bent at extreme angles at high lengths would be way less of a problem for you.

Maybe you should get 'fit' by a bicycle store to a road or mountain bike frame. They will most likely tell you you need an extra large frame.

neptronix said:

Okay, so the the rear bag is not loaded, which is good.. but 230lbs of you is upright and leaned way back, which is creating the rear stress on the rear. The angle of the seat post is another concern..

And you should have what we call an extra large frame if you're 6 foot tall, but you're riding what looks like a medium from here.

If you have shoulder pain when leaning forward on a roadbike, you need to work on your upper body strength AND your posture. I would bet that your biomechanics are off from a lifetime of sitting at desks and using things designed for much shorter people causes you to hunch forward and thus your muscles and cartilage wear pattern are way off balance. I'm 6 foot tall but with long limbs and had this problem too until i started paying attention to it and began correcting it.. now i can handle a road bike ( after 4 years of correcting my forward hunch ), which balances more of your weight forward.. and improves aerodynamics massively

Nonetheless if you want to continue putting a majority of your body weight on the rear, you're going to need a frame designed with that in mind. One that is rated for over 300lbs will be necessary.

However, finding a suspension seat post will always be your problem if you continue to rely on messed up geometry. If you had a bike frame that's appropriate for your size ( IE, handlebars forward by 24-50mm, and seat tube just barely sticking out of the frame ), these problems with things being bent at extreme angles at high lengths would be way less of a problem for you.

Maybe you should get 'fit' by a bicycle store to a road or mountain bike frame. They will most likely tell you you need an extra large frame.

Click to expand...

well it wasn't so much of a road bike but a trek hybrid,so i wasn't hunched forward. actually at work i usually don't hunch forward, but actually sliiiiiide back unknowingly till my head is below the seat rest. i don't notice it happening cause i'm so focus.

i DON'T want to be leaned that way back, i really don't, what mattered to me first was suspension, that's why i got a cane creek, and had fitted the breezer adapter for the b190, the sitting position to the rear was an unexpected side effect, i would not have done had i known what's to come (well , you learn)
further more between you and me, and.. well the rest of the world i suspect it caused my hemorrhoids (even though all my family has it) . right now due to not treating i have anemia (blood hb around level 8) , because how cane creek was configured especially with b190.

so all that is meant to go away, i've obtained a "regular" suspension seat post https://www.sjscycles.co.uk/seat-posts/254-mm-black-humpert-sp-20-suspension-seat-pin-350-mm/ which doesn't need a breezer adapter, and i won't be able to adjust the angle, so that means by definition, i'll have to be forward, and i'll have to adjust the seat tube to be more forward.

this is what i have on my paratrooper pro ,although i don't know it's seat tube angle. i feel you may mixed up between all my frames, the custom frame was built to my size, but the paratrooper pro is 20" frame because that's the biggest one they had)

additionally i wanted a longer triangle which might also affected the geometry because i planned on using a triangle battery of 52v14ah 123 lifepo4 cells (which turned out to be a bust) now with 18650 cells the triangle can be much smaller, so the reach to handle bars would be easier.


the venzo frame is 20" as well cause that's also the biggest frame 29er with 68mm, but i want to use it as sort of mock up for the future custom frame to see how it would feel like, it's seat tube angle is meant to be 73 degrees (vs 71 in my custom frame), for my understanding (at least in regards to trek sizing, the sizes i need are around 21"-21.5") , so if it works out, the custom frame should be similar only 21".

because of what happened earlier, i want to be more "hands on" with frame design, that's why i got the http://rattlecad.sourceforge.net/, but i'm not famliar with all the terminology and consideration used for the angles, that's why i ordered some books, and started yt vids about frame design, before i'll start drawing a design.

Well, to begin with, its fairly obvious that your other bike did not fit your body at all. That's your starting point, getting the right size frame for you, and likely also modifying it for utility or touring use, vs a tucked stance for aero efficiency. You might need riser bars, cruiser bars, whatever gets your weight off that part of your crotch the saddle was pinching. Angle of saddle is totally dependent on height of bars too. Your bike was way out of whack.

The reason I suggested a longtail, is because the extra length of it greatly reduces the strain on the frame, and or, your lower back.

Nothing to do with ability to carry 400 pounds, some longtails are no better frames than any regular bike. Like all bikes, they still try to be light, therefore, they can still have a weak point like your other frame.

But the thing about a long bike, is the seat, and the weight of you, is not directly over the rear wheel. Its in the middle. so on bumps, the rear wheel rides over it with out having to lift your ass. It teeter totters. This is greatly reducing the load on the frame, it just rocks rather than lifting the saddle up and down.

I'm not calling your bike loaded with crap. But it IS loaded. Then you shifted your weight back, making it worse. Your new frame should be stronger, and able to handle it better.

But it wont ever, ever handle as good as a longer wheelbase bike. Even a few inches, like beach cruiser frames, makes a big difference in handling. There is a reason every motorcycle is longer than a typical bike, particularly mtb's which are short for better handling with light loads and lower speeds.

The Thudbuster should help reduce shock loading on the frame, so is probably a good thing. I have never seen one break, but I do recall seeing a notice that certain ones were recalled for breaking like that.

fechter said:

The Thudbuster should help reduce shock loading on the frame, so is probably a good thing. I have never seen one break, but I do recall seeing a notice that certain ones were recalled for breaking like that.

Click to expand...

no thud buster for me never again, not only because it shifts my position back, but all the new ones comes with 2 bolts configurations which makes mounting a b190 problematic, its' shame i know, but i'd rather play it safe and centered...

One last consideration would be to have your frame builder weld a new rear triangle which could be configured as DD suggested and angled to provide the best seating position for you (sorry to repeat if this is what you meant DD).

2old said:

One last consideration would be to have your frame builder weld a new rear triangle which could be configured as DD suggested and angled to provide the best seating position for you (sorry to repeat if this is what you meant DD).

Click to expand...

there 2 problems, the first my original frame builder is no longer in the country so i can't exactly ship it to him, also DD says (i belive he's right) that entire geometry is messed up even the headset

dogman dan said:

But the thing about a long bike, is the seat, and the weight of you, is not directly over the rear wheel. Its in the middle. so on bumps, the rear wheel rides over it with out having to lift your ass. It teeter totters. This is greatly reducing the load on the frame, it just rocks rather than lifting the saddle up and down.

Click to expand...

Allow me to demonstrate exactly what dogman was saying. Here's a picture of me from 2012 when i was about 100lbs heavier, on a 'da bomb' cargo bike that had been cut down and rewelded so that it was a 'midtail'. The rear length is about 1.5 foot longer than a regular bike.



This front fork is half compressed because my weight is almost sitting right in the middle..
This bike was actually wonderful to ride, because when the rear wheel would get hit, the front fork would partially buffer the hit to the butt.

However, this fork was too soft and not stout enough to carry all that extra weight all the time, so i didn't continue with this configuration for long.

A yuba 'boda boda' is a good example of a mid-tail bike. Unfortunately it is not designed for a suspension fork though..

https://yubabikes.com/cargobikestore/boda-boda-v3-24-speed

dogman dan said:

Well, to begin with, its fairly obvious that your other bike did not fit your body at all. That's your starting point, getting the right size frame for you, and likely also modifying it for utility or touring use, vs a tucked stance for aero efficiency. You might need riser bars, cruiser bars, whatever gets your weight off that part of your crotch the saddle was pinching. Angle of saddle is totally dependent on height of bars too. Your bike was way out of whack.

The reason I suggested a longtail, is because the extra length of it greatly reduces the strain on the frame, and or, your lower back.

Nothing to do with ability to carry 400 pounds, some longtails are no better frames than any regular bike. Like all bikes, they still try to be light, therefore, they can still have a weak point like your other frame.

But the thing about a long bike, is the seat, and the weight of you, is not directly over the rear wheel. Its in the middle. so on bumps, the rear wheel rides over it with out having to lift your ass. It teeter totters. This is greatly reducing the load on the frame, it just rocks rather than lifting the saddle up and down.

I'm not calling your bike loaded with crap. But it IS loaded. Then you shifted your weight back, making it worse. Your new frame should be stronger, and able to handle it better.

But it wont ever, ever handle as good as a longer wheelbase bike. Even a few inches, like beach cruiser frames, makes a big difference in handling. There is a reason every motorcycle is longer than a typical bike, particularly mtb's which are short for better handling with light loads and lower speeds.

Click to expand...

well i believe the broken frame actually DID have longer chainstay , if i compare it to ritchey p29er xl which has 447 length, and venzo bike frame (unpacked down below) which has 450 long, the broken frame was 465, personally i would have liked 470, but have a true long tail is simply not feasible as there many cases where i need to get them into elevators (for example on the train station) , and also that might attract attention.
further more the seattube on the broken frame was 21.5" which i believe is considered XL standards.

if the price i need to pay for not having a long tail, is to use a rack that attchees to heat tube (i don't know if that makes a difference) or not having a rack at all, that's unfortunate.

as i said my builder recommended on using tandem chainstay for better durability, i'd probably go with that.

depicted down below is venzo's frame geometry, while it's only 20", i wanna try and use it as prototype to get a feel on the angles (heat tube and seat tube)
then if it feels good use it as a basis for modifications, for example specify to 21.5-22" make the chainstay longer and tandem strong, etc..
this is because i don't exactly all the parameters used for creating a frame (which is why i bought 2 books on the subject but they don't cover mtb frames)
https://www.amazon.com/Lugged-Bicycle-Frame-Construction-Third/dp/1492232645
https://www.amazon.com/Creative-Bicycle-Design-Framebuilding-Foster/dp/1512242799/

Neptronix mentioned mid sized cargo bikes, I think the Kona “Minute” might be worth looking at, a smaller version of their “Ute” cargo bike. If I ever see one in decent shape for sale used I’ll snag it, ever since I heard about them I’ve wanted one. They look like a comfortable ride that could hold some weight and well designed.