Well, you've already gotten many responses to this, including several that recommend to stop riding the bike, and you are determined to keep riding it. So ride it. You can keep it on the road until it falls apart under you.

You were the one who asked to stop beating a dead horse...

I also tend to side with CACycling's take on how it will go.

The extremely short length of this seat tube is putting a serious load on that upper weld. The setback post isn't helping either. Given all this it's hyper important to mark the ends of the crack with something to allow you to monitor the growth of this crack. You say you've been watching it for 3 months. But when something grows slowly our mind plays tricks on us. So marking the ends with a small permanent marker or paint is the only accurate way to track the growth of this crack.

If you find that it grows another mm or two over a few rides then the seat tube is in an active process of tearing away from the weld. If the crack lengths at all during use and with monitoring after each ride then once you notice definite growth that you can't say is a trick of your eye then it's time to stop riding this frame RIGHT THEN. Not later, right then. With each mm of growth in that crack there's more load put on the remaining metal. And that metal is already working at fatiguing. So it won't take much before the saddle suddenly folds back and down on you and into the rear wheel. While it won't snap off with a big CRACK! it will let you down in a rather dramatic way and likely cause you to crash. If this happens around traffic the resulting accident may be more than you bargained for.

Obviously suspensiom frames don't fit you all that well. For your next one may I suggest a regular double triangle non suspended frame? You'll get the cockpit spacing you want without needing to resort to oddball set back posts and at the same time you'll get a rigid frame that is accepted by most folks as being a lot more efficient to pedal thanks to no energy being sucked away by the suspension. If you really must have some extra cushion for your backside then go for a suspension seat post instead.

An oncologist friend of mine jokingly says that he cured cancer if his patient dies from being hit by a bus before the cancer gets him.

A bit of that logic applies here. The fact that the crack propagated to the point that the seat tube extension was weakened over 80% then stabilized, points to it's no longer being an issue. If you consider that the seatpost carries the load past the crack you can see why it's no longer spreading.

I suspect that the seatpost itself is slightly more flexible than the seat tube, and when flexed back overloaded the tube and cracked it above the weld. Now that it's cracked the upper part of the tube is free to flex with the seatpost and that's why the crack isn't spreading.

As long as the seatpost is of decent quality, and adequately strong for the OPs load, and is insereted so the minimum insertion is below the crack as it seems to be, he should be OK.

OK, that is, as defined by my friend the doctor. Odds are that this crack will not be the cause of a sudden failure, and I'll bet that when failure comes it'll be elsewhere in the frame.

One step I would take is to lift and inspect the seatpost from time to time.

Riding that bike is stupid. I would like to be more polite about it, but I feel the need to be blunt.

The smart thing to do is retire this bike for now, buy a garage sale beater for ~$25 and fix the mountain bike (replace the frame with a decent rigid one, get a good suspension seatpost when you can) when you get a chance. You can get a bike at a garage sale for around the same price as buying the materials necessary for your bad-idea-repair job.

I am familiar with those entry-level specialized full suspension bikes, and while I have not seen too many of them fail, the frames aren't so great that they are worth saving if they do.

Your explanation of why steel fails more quickly than aluminum is erroneous for two reasons - (1) steel does not fail more quickly - it usually deforms or bends before failure, and (2) the stiffness or 'springiness' of steel has nothing to do with failure.

1. Causes of failures of bike frames
In my experience, there are two main reasons why bike frames fail - either from a crash, accident, cased landing from a jump, etc. that exceeds the strength of the frame, or from a mistake in manufacturing that causes a joint or frame component to be weaker or more brittle. In the first scenario, steel has the advantage of bending considerably before breaking, and many accidents will result in a bent or mangled frame that may still be somewhat rideable - if only to get you home or to safety. Aluminum has far less ductility (the amount it can deform without actually snapping) so if you crash an aluminum frame hard enough to exceed the material's strength it will usually simply snap. Watch people riding bikes though any large city and you will see many who have had crashes on their bikes hard enough to bend the frame, but keep riding them anyways - usually the headtube is bent backwards, the front wheel is a little too close to the pedals, and there are 'wrinkles' on the bottom of the top- and down-tubes. I don't think I have ever seen an aluminum bike with similar damage - when you crash hard enough to bend the frame you almost always break the frame.

2. Material Properties
The other problem with your argument is that, while steel is 'stiffer' (higher modulus of elasticity than aluminum), aluminum frames almost always have much larger tubes and much thicker walls to make the frame acceptably stiff and strong. THe result of the larger tubes with thicker walls is that the actually deform less under load - not more... Aluminum bikes are often 'stiffer' than steel bikes, and they get this way by each of the individual frame components being made stiffer.

I did not say that steel fails more quickly than aluminum. I said that it fails in a different mode than aluminum does. The stiffness and/or brittleness of the material has everything to do with that failure mode

My experiences with aluminum frames and aluminum parts is that they almost never 'just snap'. They crack but they don't just snap as in 'I was riding along and the bike just snapped into two pieces'. I had a Specialized
Stumpjumper M2 frame that broke. It didn't snap, it cracked at the welds much like Geosammy's frame did. And that's for an aluminum matrix alloy that is far more brittle than other aluminum alloys.

I broke another frame above the seattube/toptube junction because I was using a seatpost with a huge setback like Geosammy's. Again it cracked and tore rather than fractured.

I have had numerous wheels fail because of cracks or because the spoke pulled out or because the sidewall thinned too much. I've had rims that have cracked completely around the rim...360 degrees... on the inner wall. There was no fracture and only some creaking of the wheel while riding.

I've had a crank arm shear off which is the only case I have ever experienced where an aluminum part actually fractured. However the crank arm creaked a lot before failure...which I ignored After the part fractured, I could see dirt and grease in the leading edge of the crack which indicates to me that it took its time in breaking.

On the other hand, all of the steel parts and frames that have failed through breakage have been fractures. No bending. No warning. And usually associated with a load pop or tink or pink or plink or whatever other onomatopoeia you'd like to use. I've broken pedal spindles...riding along and suddenly I've got a pedal attached to my foot and it's not attached to the crank. I've broken axles which let go with a loud tink and then one of the frame dropouts broke too. I hit a curb with a kid trailer, turned the trailer on it side and discovered a broken...not bent or deformed but broken...axle. I've broken another frame while climbing out of the saddle. I heard that familiar tink and the one of the dropouts was broken. The sound that fracturing steel makes is very familiar to anyone who has ever broken a spoke.



Aluminum just doesn't make that kind of sound nor does it just fracture like steel can. Even in crashes, aluminum don't shatter. It deforms and tears. I hit a curb with a Manitou II fork at about 25 mph. The fork's crown was bent, mangled and torn but it wasn't fractured.

As you can see, I've had lots of experience with parts failures of both kinds of materials. I have even had some experience with bending steel frames. Yes, they bend and deform more than aluminum. And they aren't likely to fracture in a crash (but then neither is aluminum).

Aluminum frames use larger diameter tubes to make them stiffer because small diameter tubes would require thicker walls (and more weight) to achieve the same result. You could easily make steel bikes with larger diameter tubes but the frames would be so stiff as to be unrideable. But this really has nothing to do with the discussion at hand.

Any argument about whether steel or aluminum is more prone to brittle failure (snapping vs, bending) is pointless.

Both materials encompass numerous alloys and conditions (temper). Many steel alloys can be heat-treated to properties ranging to almost silly putty-soft to glass hard, likewise with aluminum, though it's range is usually narrower.

The mode of failure is also influenced by design and assembly factors, such as cuts, notches, plating, welding, etc, and by the degree and number of flex cycles to which they're subjected.

Without dealing in the specifics, debating predicted modes of failure is like arguing about which river is deeper, the Hudson or Mississippi.

All that being true, ask any bicyclist about how a steel part or frame fails vs how an aluminum part of frame fails and the vast majority are under the mistaken impression that aluminum is like glass. In other words, it's going to shatter into a million pieces. That has not been my experience.

Ductile failure isn't an inherrent property of either material, its a sign of good engineering. Whether working with steel, aluminum, or titanium, parts can be designed and materials spec'ed with consideration to the mode of failure. Ductile failure over time, even a fairly short time, is preferable to sudden unannounced catastrophic failure, and good designers build that in whenever possible.

Where it isn't built in, knowledgeable consumers can select parts with that in mind. It's one reason that, despite lighter stronger alloys being used today, I still ride with 2000 series aluminum handlebars.

I have marked the ends of the crack. This is how I can tell that the crack hasn't grown any larger in nearly 3 months.

Thanks FB... Have always taken out the seat-post every month when I do a cleaning.

If you want to spend some money, you can wrap it the whole area in carbon fibre to reinforce it. They sell small kits on ebay making custom parts. They're at least 30$ I think, so you might be better-off saving money for nashbar frame or a used one. It took a few days for me to do all the layers with the carbon, so that was a cost as well. I wrapped a broken chainstay on a nice specialized sirrus I got for 30$. I've ridden it hard and far in the last year without any worries. YMMV, as our cracks were in different places and caused by different things.

(FWIW I wouldn't do this in your case)

While good engineering may be necessary to have ductile vs. brittle failure, you also need a ductile material. Most steels allow ductile failure and most aluminums do not... not enough elongation or deformation can happen before breaking.

Anyhoo, failure is failure is failure. After a frame has failed it should no longer be ridden. I am constantly frustrated by advice on here by people who do not undestand what 'failure' really is - there are many reccomendations to continue riding bikes with mangled steel frame because they think there will be some further 'warning' before failure... well guess what? The bending is the 'warning' and the next step is snapping in half and leaving your face spread down the pavement.

I am happy to report that noone in this thread gave the OP this dangerous advice, and when his frame finally finishes snapping in half he will have noone but himself to blame and help him get around in his wheelchair.

I wouldn't expect it to be all that spectacular... although as one poster noted, it could be pretty ugly if it causes undesirable interactions with traffic...

This is an update to my "Crack in Frame" post.

I didn't make any kind of repairs of this failure/crack in the frame.
I did however, continue to ride the bike up until my recent purchase of a new bike, without a catastrophic failure of the frame.
I'd like to thank everyone that commented on my post and for those that offered some sound advice.
Needless to say, I didn't heed this sound advice. I rode this bike until it's end. The only thing left of this bike is the front fork. Any part that could be salvaged was and used as replacements for the more inferior parts that came with the new bike I'm now riding.

Glad to hear it! What type of bike did you get as a replacement?

FB; 100% agree on causal assessment. The root cause of that is usually a frame that is a few inches too small, leaving the rider to jack up the seatpost which is then coupling with the design that has the extended seat tube as you mentioned. The crack is predictable.

- To fix the frame well enough to ride, I would want to ask my local welder (a TIG qualified one) to run a weld right through the middle of the crack and a big beyond the ends. It would be smart to take out the seat post before welding (hah) and it may be necessary to run a seat tube reamer afterwards. If desired, one could file down the weld bead afterwards and spit a bit paint on it.

Would be putting in an extra long post after the repair, but I always try to use an extra long seat post even on a steel frame.

In a standard double-diamond frame, esp. one with an extended seat tube rising above the seat stays and top tube, not having enough post inserted is almost always the cause as any force int he seatpost is transferred directly to the top of the seat tube juction. Hoever, the OP's frame was most certainly NOT a double diamond frame (no seat-stays, very short distance between the top welded joint ont he seat tube and bottom welded joint on the seat tube... no matter how much seatpost was inserted into the frame, every bit of force on the saddle was resisted by the joints between the top tube/'down-tube' (for lack of a better name) and the seat tube. The OP said he cut an inch off his seatpost to get it to fit, which indicates he had less than the maximum height you would normally have with a full length seatpost, and likely the remainder of the post was damn near the bottom of the interrupted seat tube.

No matter, he has since retired that frame, anyways.

New frame, [check] and Hacksaw a chunk out of the old one so No One else try's to use it.
recycle the Aluminum.

I'd drill out the end of the crack to try to stop it propagating. Any size drill is useful, as big as you dare without weakening other stuff.

If you can slide the seat forward that will help, as will fitting a post with less layback. You might then want a longer stem.
I'd fit aero bars since it is a commuter, that will get your weight off the seat and give extra zoomage, win all around.

I replaced the old bike with the 'GT Sensor 3.0 Mountain Bike' at a price tag of about $1400 it was a step up for me in price, but I deserve it.


Some of the new bikes features include...

*Hydroformed 6061 frame
*120mm-travel Marzocchi fork
*Trail-taming X-Fusion shock
*Shimano 30-speed drive-train
*Avid Elixir 1 hydraulic disc brakes
*WTB Volt Comp saddle

Just to name a few.
I felt terrible about retiring my old bike, but that quickly went away after a tour around town on the new one.

Congratulations.

FB was right again (the post where he mentioned his oncologist mate).

Yes I guess he was at that. It was inevitable that it was going to be replaced. I just had to save up some money and find a bike that I felt comfortable with.

Don't know where you live, but if there's a co-op nearby you might be able to pick up a frame cheap, and then transplant your parts to it. I've helped people do this more than once (I work at a bike co-op, in case it isn't obvious) .

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