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Discussion Starter · #1 ·
A little context: I am 6'5 and around 215 lbs, give or take a few depending on the time of year, and just this past week had the frame of my main bicycle fail. It is an aluminum frame endurance bike from a name brand and developed a crack in the seat tube a few millimeters above the top tube weld (between the seat post clamp and the top tube weld). I have taken it to my LBS where I purchased the bike a little over a year ago and warranty procedures are under way.


This is the second bicycle frame I have had fail. Previously I had the seat tube on my old hybrid shear a few centimeters up from the bottom bracket. I was around 250 lbs when I purchased that bike and started riding. I put a good 5 or 6 years on it doing city commuting and weekend rides. I was a little surprised it broke the way that it did, but I put a lot of wear on it. Not so much with my newer road bike that just broke this past week. Summary over.


The guys at my LBS have been extremely helpful (even since before I purchased this bike from them) and I dont think they were giving me a line of marketing BS (they were not trying to sell me anything), but I wanted to get a second opinion from the community. I asked them what I could do to prevent these types of things in the future. I know I am a big guy, but I'm not huge. This failure rate seems a little too frequent (in my relatively uninformed opinion). They said there wasnt really an answer and that frames fail. They did suggest that the allowed flex in carbon fiber frames will cut down on stress fractures like what just happened to my road bike. They were also saying that CF bikes can be built more to purpose and adjusted based on the size of the bike and rider so that stressed areas get built up more.


Im just not sure what the answer is to reduce frame failure rates. Steel? Titanium? Custom built so that I actually get a properly sized bike for me?


Im curious if other people experienced in the industry have any thoughts on failure rates, merits of frame material X versus Y, or general advice for frame styles/types for those of us who barely fit 61cm mass produced bikes?


Thanks!
 

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I'm guessing the seat posts you use have setbacks to them. This increases the stress on the seat tube.

If you can find a larger frame that will allow you to run a zero offset seatpost that should help keep the frames from cracking.

Other than that running larger tires at lower pressures can help. They'll take some of the bounce out of your seat and some of the stress then off of the seat tube.

Other than that you'll probably just have to lose some weight. Other materials may fare better but I wouldn't bet on it.
 

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I think the 2nd failure is just bad luck, while the first was use.

On the hybrid, it sounds like you really worked the bike hard, thus it just wore out.

On the aluminum road bike, any chance you are running it with a lot of seat post showing ?, a heavier ride might stress the seat tube at that location. Maybe the frame is too compact, or a size small for you ?
 

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Bummer you've had bad luck with aluminum frames. They have poor modulus of elasticity, so can't flex under load and break. So stay away from aluminum. That's not to say some alloys aren't up to the task of supporting a big rider.

Check out Leonard Zinn's website. He's 6'5" or so and builds bikes just for really tall riders. He uses lugged steel because there's nothing stronger or with more modulus of elasticity than steel. He'll fit you on the bike properly, too.

Bianchi has made 62 cm. frames out of steel. There are others out there in 62 cm. sizes. Custom might be the way to go. Have you checked the fit programs like wrench science or Colorado Cyclist?

If you're breaking frames, definitely stay away from aluminum. Carbon also breaks under stress way sooner than steel, so I'd go with steel for your style of riding, which could contribute to frames breaking.

Rode with a kid who just whacked up the hills out of the saddle. After a year of doing this on a badly brazed steel frame, the seat tube broke at the bottom bracket weld. Too much heat was applied in the welding, the tube was brittle, wouldn't flex, and broke under the lateral stress induced by this rider's out of saddle climbing style. He pedaled the same way seated. He broke his next frame, this one aluminum, at the seat stay - seat post join, again from wild out of saddle flexing. A hand brazed steel frame would probably hold up the longest for him.

Good luck. Large frames are hard to find.
 

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Some anecdotal information.

I am bigger than you (6'5" 240lbs currently, down from over 300lbs).

My main bike has been a Carbon BMC Gran Fondo (61cm). I have about 15k miles on it so far, and no signs of cracks, etc...

I have some newer bikes with less miles. A Volagi Viaje Ti, and a Norco Search. The Viaje has about 2k miles on it, and the Search about 1000. They are both also holding up well.

The BMC in particular impressed me. I've been doing 200 miles a week and have 6k on the year so far. It's seen me through 60lbs of weight loss and has held up well. I don't believe the designers had me in mind when they made it, but the bike seems well suited to clyde duty. It also happens to be *very* comfortable, due to the compliance in the seatpost/seat tube/seat stay.

Edit: Here's a picture showing the seat tube/seat stay angle. It's pretty extreme, but it's carried my fat ass around for a lot of miles, comfortably.



Also, FWIW, I agree with frederico about the Aluminum frames not being ideal for big riders, and steel being good. But I disagree about Carbon. Certainly not all carbon frames are made the same. Budget/low end frames that are just scaled up for larger sizes are probably not ideal, but if you find something like I did, that is well engineered and well made, Carbon is fine. Also, be sure the warranty is good.
 

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+1 On Zinn. He makes some huge bikes and he's a super nice guy.
 

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Alum is not so good on stress near failure loads with cyclic loading. I think you would be better on a CF with a setback SP. I would go that route vs a oversize frame with zero SP.
I would go with a CF with a more traditional toptube vs a compact sizing sloping TT. Migen has alot of SP exposed, don't know if that is for you.
 

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Discussion Starter · #8 ·
That is an interest point about the setback on the seat post. I was recently in the process of replacing my old seat post and picked up a Thomson with setback. It turned out that despite the post on my bike having setback, that the Thomson had too much. I had just returned it and was going to get a no setback post but then the whole crack thing happened. It might be the case that I can get away with a zero setback post.

On the weight side of things, I certainly could lose more weight but that will require a serious increase in effort (both riding more and further altering diet). It would certainly be a good idea in the long run, both for me and my bikes, but Im fairly content with where I am at right now.

Ive been running 700x25s around 90-100psi. I need the high psi to not get pinch flats and chew up the rims. The frame could probably support 28s, but I dont think anything bigger would fit. It is certainly something I will consider in the future.

Thanks for the feedback MMs.
 

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On the tire size, you did not mention what wheels your running. Just remember that with bigger tires, and a broken spoke your ride is done, unless you have a high spoke count wheel, your situation may very but everyone has their own issues based on what they specifically are running.
 

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How far is the seat post inserted into the seat tube? With your frame size, I would use a seat post that inserts at least 2-3 inches below the bottom of the top tube.
 
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Discussion Starter · #11 ·
Great info, thanks!

Im going to be getting some sort of replacement via frame warranty. But I will definitely look into Zinn for any future bike purchases. I have heard of him and he has a stellar reputation in the frame builder world.

Im in Philadelphia which is pretty much just flat. So I am not hammering up a lot of hills or anything and dont do much out of the saddle riding. I also do what I can to work on spinning pedal technique rather than hammering.
 

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Discussion Starter · #12 ·
The wheels are high spoke count (32 or 36, dont remember which off hand). I have broken my fair share of spokes and am very familiar with all that.
 

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Discussion Starter · #13 ·
I had quite a bit of seat post showing, but there was still ~2 centimeters of room to the minimum insertion line. I am not sure off hand where the bottom of the seat post tube was in relation to the top tube weld. I would guess that it was around where the crack developed, which would mean it was above the weld.

The bike is a 61cm frame (largest the brand makes) and the seat post was 330mm. It was the appropriately sized piece according to that manufacturer.
 

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Discussion Starter · #14 ·
Some anecdotal information.

I am bigger than you (6'5" 240lbs currently, down from over 300lbs).
I have heard similar things like this before and it is somewhat comforting to know that carbon fiber can hold up. I suppose it all depends on the brand. When I was in the market for the current bike that just broke some folks at various LBS in my area suggested carbon fiber for larger riders. The cynic in me just figured they were trying to sell me a more expensive bike. I ended up with the aluminum for budgetary and other reasons.
 

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A lot of good advice here.

I too question whether the 61cm frame is tall enough for you. I wonder whether you had adequate seat post length in the seat tube to reinforce the area where the crack occurred.

I also think it would be worth looking to Zinn for a frame. Also, stop at Bilenky Cycle Works in Philadelphia. Talk to them and they should be able to build a tall enough frame for you with clearance for larger tires. (I have a custom Bilenky frame. It's my second frame from them.) My Soulcraft Royale for instance, has short reach brakes and a steel fork. I can fit 28mm tires with plenty of room to spare, back AND front.

Your weight definitely has something to do with it. I'm sure you can put out some serious force to the pedals, which is likely flexing frames a lot.

What the dealer told you about carbon vs. aluminum and breakage; it's partially right. Aluminum hates ANY flex, and cracks microscopically when it's flexed. The micro-cracks add up, then the frame develops a real crack. While carbon can be designed to flex as your bike shop designed it to, unless you talk to the frame designers themselves, you have no idea whether the frame was designed with you, your height, and weight, in mind.

One option is to sell the warranty replacement to partially fund a more appropriate frame.

And lastly, 2 points does not plot a trend so I don't think you have enough historical information collected to definitively say it's your weight and height that's breaking frames (which sounds like it contradicts all of the above!). Nevertheless, after you break your 3rd frame, you may better determine whether you're the cause and need something special.
 

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Discussion Starter · #16 ·
Thanks for the suggestions, Peter P. I think you are right on with pretty much everything you said. Unfortunately, the timing is just not right for trying to sell frames to fund a different bicycle. I am going to have to take what I can get with the warranty and use that in the mean time. This discussion has given me a lot of things to think about and consider for future bike purchases though.
 

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that is a classic failure for aluminum - seat collar area. I had it happen on my Klein 25 years ago too.

Carbon, steel or Ti are all much less prone to this issue. Alu has rapid fatigue properties that require a lot of engineering-around. But this issue is solvable. I mean today most mtn bikes are still aluminum frames and are not failing en masse.

your weight is nowhere near any range that would compromise any frame from reputable makers today. I recently sold my 2001 aluminum road bike, and it was faultless despite me being heavier than you.
 

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good post. 61cm is a size for me at 6 4. and I have to have post and stem really far out . at 6 5 that might be a 'cantilever too far'

yeah that Zinn guy is super tall and knows how to engineer a tall bike!
 
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