Mountain Biking - softail frame durability

Hi everybody. I just snagged a frame from a buddy of mine while he upgraded to a SWEET ellsworth truth. My new frame is a steel DEAN jester softail, with a stratos XC pro shock in the back and about 1.8 inches of travel. the frame rocks, is very light, fits me great, and in general is a whole lot of fun.
Now, my worry is that this is a 6 year old steel softail, and those chainstays have been flexing a whole bunch. should I be concerned about these guys snapping off on me or anything?
I don't take it off 4 foot drops, just general XC riding.
anyone have experience with these before?
thanks
travis

With steel so long as you stay inside the design parameters you're fine. Aluminum would fail eventually.

A fatigue limit is the load bearing limit of decline in strength a material reaches after it has been fatigued/cycled a certain number of times. This strength is also known as fatigue strength. Having a fatigue limit is a good thing. It means that the strength cannot drop any lower as the material is continued to be cycled. The fatigue limit can often be seen on an S-N plot. Here's a generalised S-N plot comparing steel and aluminum. Stress is on the Y-axis and cycles is on the X-axis.

http://ussautomotive.com/auto/images/steelvsal/fatigue_comp.gif

Notice the fatigue or endurance limit of steel. This plot shows that as long as the loading for steel is below that fatigue strength, it can be cycled forever. You don't have to take into account lifespan. However, if you look at aluminum, you must always ensure that your loading follows underneath a continually falling curve. Since you can't always ensure that then you need to design the structure more conservatively to keep the loading underneath the curve for a given lifespan. So let's say you assume the "established" cycle-life of aluminum (500 million cycles). You will then want to keep the loading less than the fatigue strength of aluminum that's rated at 500 million cycles. In this case that would be maintaining a stress load below 124MPa or about 18,000PSI. However, because of the way the curve goes, if you introduce greater than 124MPa to the material that has been cycled beyond 500 million cycles then it will wail. I hope this clears things up a little bit.

Can we sum this up into a very blunt bottom line? Because reading 2 paragraphs of text loaded with scientific terms doesn't really... help...

Is this basically saying I can beat the crap out of a steel frame and it will last longer than an aluminum frame under the same abuse?

Can we sum this up into a very blunt bottom line? Because reading 2 paragraphs of text loaded with scientific terms doesn't really... help...

Is this basically saying I can beat the crap out of a steel frame and it will last longer than an aluminum frame under the same abuse?


I guess that's what he's saying. Unless of course the steel frame gets killed by RUST first! :)

I guess that's what he's saying. Unless of course the steel frame gets killed by RUST first! :)
With proper care a steel bike will last forever
An aluminum bike has a point at which it WILL fail. (Which is why myself and others advicate replacing aluminum after about 5 years) Abuse will kill any frame due to the fact that you're loading it beyond it's designed parameters.

With proper care a steel bike will last forever
An aluminum bike has a point at which it WILL fail. (Which is why myself and others advicate replacing aluminum after about 5 years) Abuse will kill any frame due to the fact that you're loading it beyond it's designed parameters.


Granted. Abuse will kill any frame regardless of what it's made out of. But I'm just trying to understand what you are trying to say.

Are you saying that with everyday easy easy easy easy road riding to the supermarket, an aluminum frame will die first?

Heavy riding? Competition? Jumping a few curbs? I'm not seeing the big jump from steel to aluminum here...

Are you saying that with everyday easy easy easy easy road riding to the supermarket, an aluminum frame will die first?



Aluminium will fail eventually, how soon depends on how it's used. But don't make the mistake of assuming steel is indestructible, some people are pushing steel so far in an attempt to compete with aluminium on weight that failures aren't unheard of. I've seen newish steel road frames fail catastrophically, and my Pashley trials frame definitely wasn't indestructible.

I don't know much about Dean Jester bikes to comment about your particular frame but as long as there are no visible cracks the flexiness is almost certainly no worse than it was when the frame was new. You'll just have to trust that the designer took the fatigue limit of the material he used into consideration.

thanks everyone, I'll let you know if it falls apart.
with regards to the steel VS aluminum, how does titanium measure up? will the Ti frame last forever?
thanks
-t

how does titanium measure up?

I don't have any graphs or charts but you can think of titanium as lighter steel that has a higher corrosion resistance

Titanium is nice, I would get it if i could afford it. One of the people i ride with sometimes has a titanium frame, and I think he has had it for nearly 10 years. Also, money is less of an issue with him

Titanium is nice, I would get it if i could afford it. One of the people i ride with sometimes has a titanium frame, and I think he has had it for nearly 10 years. Also, money is less of an issue with him


So I assume he has special tools for that bike? I heard that you can't use normal tools with Titanium because it corrodes the metal. Like for the SR-71 Blackbird spy plane :D

Steel frames do not last forever any more than alu or cf or ti. Weight limits prevent you from building a steel frame where loads stay below the fatigue limit.
See http://www.damonrinard.com/EFBe/frame_fatigue_test.htm

With steel so long as you stay inside the design parameters you're fine. Aluminum would fail eventually.

If you don't know what the 'design parameters' are and don't know how to stay within them, your statement has little practical use.

If alu is flexed it has a limited life.
Steel may flex for a long time with no problems.
Steel bikes are designed to flex, keeps the welds together.
Alu bikes the flex is designed out or makes a finite lifespan.
Probably with the seatstay stresses, the shock will help the bike last longer.
There are a few designs by HQ mtb builders, small production #'s.
http://www.oldmountainbikes.com/cgi-bin/bikes.cgi?bike=S0P%200379 A nice one.

I ride a 2000 Jester. Great Bike

The frame rocks, is very light, fits me great, and in general is a whole lot of fun.

Ride it until it breaks!

Seriously, have fun with it, and just don't do any foolish 5 foot drops. The frame should be fine. If not ...... they make them every day. :)

Do you have any pix??????

So I assume he has special tools for that bike? I heard that you can't use normal tools with Titanium because it corrodes the metal. Like for the SR-71 Blackbird spy plane :D

Specialis tools as in regular tools you would use to tune a bike? I wouldn't think so since generally when you tune your bike, the tools don't really touch the frame a lot. But if you were building up the frame and had to face the BB and chase all the threads and what not, I am not sure if you would need diff. tools...