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I've gone through four frames in the last decade or so, all from different manufacturers, all steel but both lugged and welded. Every one of them has eventually developed a crack, been repaired and then re-developed more cracks until I give up and get a new one.

It's usually on the seat tube down near the bottom bracket, but once on the down tube near the headset, and once on the chainstay after the seat tube had been repaired.

I generally just use the bike for commuting (~150k / week) and occasional weekend riding - all on the road. I've been on my mountain bike for the last couple of years, but I miss my skinny tyres and I'm thinking of getting a new road bike. So is there anyhing I can do to make it last longer than a couple of years or should I give up and just stick to mountain bikes?

Does this point to there being something wrong with the way I ride? Do you think doing track stands at lights would exacerbate the problem?

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What make of frames were these? How much do you weigh? –  whatsisname Dec 15 '10 at 16:47
    
Do you keep the saddle at the proper height, legs straight at the end of your pedal stroke with the heel of your foot on the pedal? If you keep the saddle low, you might be putting more weight on the saddle than you should. I suppose it's possible that could be stressing a weak frame a little bit. –  Neil Fein Dec 15 '10 at 22:15
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Just a thought: Where do you store your bike in the winter? Going from sub-freezing to room temperature multiple times a day could also be hard on welds, although any decent steel frame should be able to shrug that off. –  Neil Fein Dec 15 '10 at 22:16
    
I'm in a temperate region, it never even gets frost here. Blazing hot in the summer though (48 degrees C or more some times). Thanks for the links about the saddle. I think I'm in the ballpark as far as adjustment goes. And as for make they were three different manufacturers, one a local frame builder with a pretty good reputation, one KHS korean made in a factory and one from a LBS in Sydney whose origins I don't know. I weigh ~90kg –  stib Dec 20 '10 at 4:50

6 Answers 6

up vote 7 down vote accepted

It is very likely that you are putting too much stress on the frame when you are cycling due to your power stroke.

It took me a long time to train myself to avoid standing and powering the bike through the acceleration of starts, or even powering through it while sitting. I've long since learned that while I have plenty of power, I actually am able to transmit it more effectively to the wheel using a faster cadence with lower power.

Try to start out in lower gears so that it's easy to get up to 90rpm quickly (quickly, as in within dozens of feet, while you are still accelerating). If you don't know your cadence, or have an easy way to measure it, the disco tune "Stayin' alive" is just over 100bpm. There's a lot of other music you may be familiar with that is about 90bpm, you can do a google search for "90bpm song" and you'll find lists such as this: http://www.edenathletics.com/90bpm

The location of the stress fractures really suggests that you are standing up to push more power into the pedals. If you are doing that, stop standing - road bicycle frames are not meant to take the pounding that this type of riding entails. The standing position puts a tremendous amount of force on that particular joint, and the pedals are not long enough to really transfer that energy into the chain - you are wasting a lot of power flexing the frame. It you are a fan of geometry and physics, imagine putting the frame on two stands where the wheel hubs are usually located. Now place a bouncing 1/2 ton load on the bottom bracket. You'll find the stress fractures are disturbingly similar to the ones you are experiencing - the two triangle shape of the frame will force the top tube and seat up, while the bottom bracket is forced down, leading to fractures in the seat tube. If the seat tube is strong, you may instead fracture the chain stay on the chain side.

If you prefer that riding style, however, then you'll have to settle for mountain biking frames, which are designed for powerful stroking techniques. This is one of the reasons messengers often use mountain bikes - they are standing up a good portion of the time with very powerful strokes to accelerate in very short bursts.

While spinning doesn't allow such high acceleration it is much more efficient in transferring energy from you to the forward motion of the bike. And you can still stand up and accelerate if a situation calls for it, but doing it often is going to fracture your frame.

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Thanks for that explanation. Very clear. –  stib Jan 27 '11 at 5:33
    
What happens to the power you use to flex the frame, given that the frame does not deform? –  lantius Mar 7 '11 at 7:39
    
@Lantius The frame does deform, though different frames will deform at different rates depending on construction and materials used. The frame flexes, and then it springs back. Some of the energy is lost in heating, but that's fairly minimal. Note that the deformation is very small, especially on very brittle frames. You could see the deformation with strain gauges, for instance, but it's not something you'd be able to easily see visually since the deformation is very slight. Aluminum tubing acts like a spring when compressed lengthwise, but only for a few mm. –  Adam Davis Mar 7 '11 at 15:29

I had a run of bad luck with road frames quite a few years ago, going through about three in rapid succession. Like you, the faults were always in different places. Since then I haven't had any troubles, but I did start using a slightly higher upgrade of frame materials. I currently ride about 120K a week,mainly commuting, doing track stands wherever possible.

My advice would be to perhaps try a slightly better grade of steel frame next time. I was using low grade steel, then a couple of manganese alloy based frames, before going onto Reynolds (not too sure of the number, early 531 I think) and Columbus No.2 frames. No problems with them.

I currently ride a composite frame, aluminium main tubes with carbon forks and rear stays. Going strong since 2005. I am also not particularly light, being over 85kg at the moment (must train more!)

I just have troubles with wheels now :-(

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I was thinking about a bike with the same specs, but was worried that it might be worse than steel, with aluminium and carbon having the tendency to catastrophically fail instead of tearing like steel. –  stib Dec 20 '10 at 4:56

There are certainly techniques that will put unusual strains on the bike, track stands could be, I certainly think that excess use of a turbo trainer does. I (try) to do track stands where possible and my commute bike (~150k per week for a number of years) only died when I crashed it ...

Quality of the ingredients is certainly one factor. Another could be the manufacturer (although you have already mitigated a little for that in your question). Many people, in particular those who come to cycling from other sports, might try to deploy their power in different ways. I used to row and when I was looking at a new bike, I spotted a lovely looking candidate, but the guy in the shop said "I won't sell you that, it's a Bianchi, and I find that all big rowers break Bianchis", his theory was that lugs like me (I'm only 6' and 200lb but that's big for a racing cyclist) tend to grind out in the bigger gears while the Bianchi tended to favour the lighter rider who'll spin it higher, but in a lower gear.

So the chances are that it probably is something about how you ride, but that doesn't mean changing your style, just finding a bike designed around you.

Or maybe you should change your style ...

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I can see that being a problem with Al frames. I'm 6'2" and 210lbs. My CAAD7 roadbike frame flexes like mad when I'm really getting on it... I keep checking that one for cracks. None yet, but I guarantee it'll happen eventually. Al does NOT like repeated flexing. –  Brian Knoblauch Dec 16 '10 at 16:11
    
Hey, I'm an ex-rower. Maybe I need to learn to spin a bit higher. –  stib Dec 20 '10 at 4:47

I can't imagine what you'd be doing to it, must be defective equipment? My ancient, cheap, steel frame beater mountain bike hasn't cracked yet and it was routinely subjected to hard impacts/landings (back in my younger days... the body can't take that anymore).

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I broke two steel frames in different ways, but both were used for commuting under heavy loads.

  1. I stretched the rear dropouts of a frame built for a 7 speed hub to fit a 9 speed hub, and this put stress on the chain stays just behind the rear bottom bracket. After about 6 months of daily riding, the right chain stay cracked.

  2. I rode my bike head on and it crimped the downtube just barely enough to notice - I could only tell if I ran my thumbnail over it - and about three years later, the down tube cracked at this spot.

The bottom line is, steel (or any metal) fatigues; but in both of these cases it was helped along by my own abuse - both were learning experiences for me.

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As an avid cyclist and every day NYC bike commuter, I had a similar problem with road frames. Aluminum frames would last about 9-12 months and steel TIG welded frames generally lasted about 18-24 months before cracking at the bottom bracket (full disclosure, I'm 6'1" and 210 with all my gear).

Alas, there is a solution, with the advent of twenty-niner mountain bikes you can now get a good rugged frame (Surly Karate Monkey is my favorite) and build it up with road tires (I'm partial to Continental Ultra Gatorskins in the 25cc variety) with nice rugged mountain bike wheels (I'm using XT hubs with 700c Mavic rims). Sure your frame will weigh about 2 pounds more than a road steel frame, but it won't break.

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