Mountain Biking - Question about actual thickness in the actual frame's metal...

Is there a standard thickness that all metal is within the bike frames made nowadays? Reason I ask is when I took my seat off and the bracket to tighten it you could obviously look down into the seatpost of the bike. The metal I expected to be a little thicker, but hey I guess the manufacturer's know what they're doing. I wasn't sure if the extra heavy duty bikes use thicker metal or a different kind or what.

Kind of a strange question, I know. I just figured I'd ask.

Another side question: Does Giant use the same frame for all of their sport mountain hardtails?? (except the boulder which uses supersized steel). Reason I ask is the Boulder SE which MSRP's for 280 has the ALUXX SL butted aluminum frame. But even the Rainier, that MSRP's for 850 dollars has the ALUXX SL butted aluminum frame. I just figured the Rainier would have a different kind of frame. Is this saying the Boulder SE has a damn good frame for the price, the Rainier has a cheap frame for the price, or the frame is to a point it's so strong it doesn't matter how you use it so Giant puts them on all of the sport mountain hardtails?

Is there a standard thickness that all metal is within the bike frames made nowadays? Reason I ask is when I took my seat off and the bracket to tighten it you could obviously look down into the seatpost of the bike. The metal I expected to be a little thicker, but hey I guess the manufacturer's know what they're doing. I wasn't sure if the extra heavy duty bikes use thicker metal or a different kind or what.


A ton of factors:

1) intended use

2) frame material

3) butting

4) gusseting

5) diameter

my opinion anyway... :)

A ton of factors:

1) intended use

2) frame material

3) butting

4) gusseting

5) diameter

my opinion anyway... :)

Yeah I know, all of them in the description has the same material, butting, and gusseting... I know for a fact when I saw the Rincon in person the only difference was a different shifter and double walled rims.

I just wasn't sure if there was much of a difference. Because... I can't tell a single difference. But not just between these Giant models, with a lot of other frames out there. I mean sure diameter makes a difference and all, which I have noticed some other bikes differ. I guess it's hard to look inside the bike and see the thickness of the metal contained in the frame.

Yeah I know, all of them in the description has the same material, butting, and gusseting... I know for a fact when I saw the Rincon in person the only difference was a different shifter and double walled rims.

I just wasn't sure if there was much of a difference. Because... I can't tell a single difference.
Not sure...someone else with more experience will probably post later.

New question: I've been reading more about aluminum and steel frames. Everything I read, it's either one way or the other. It seems like whenever I find a different frame thats say steel, it just goes on and on about how great steel is. Same with aluminum. I've been having a hard time finding the actual DIFFERENCE between steel and aluminum frames.

I'm pretty sure steel is heavier, but I was under the assumption aluminum was stronger. What's the case? Can anybody clear up this confusion?

btw - what makes for a good frame? I came across this one. http://www.jensonusa.com/store/product/FR507A00-Jamis+Komodo+Fx+Frame+04.aspx
For the price, what are your impressions? (not planning on buying this, or a frame at all. Just trying to decifier the differences)

New question: I've been reading more about aluminum and steel frames. Everything I read, it's either one way or the other. It seems like whenever I find a different frame thats say steel, it just goes on and on about how great steel is. Same with aluminum. I've been having a hard time finding the actual DIFFERENCE between steel and aluminum frames.

I'm pretty sure steel is heavier, but I was under the assumption aluminum was stronger. What's the case? Can anybody clear up this confusion?

btw - what makes for a good frame? I came across this one. http://www.jensonusa.com/store/product/FR507A00-Jamis+Komodo+Fx+Frame+04.aspx
For the price, what are your impressions? (not planning on buying this, or a frame at all. Just trying to decifier the differences)
One major difference in material is rigidity. All specs being equal, Al is more rigid. This doesn't mean it's better.

One major difference in material is rigidity. All specs being equal, Al is more rigid. This doesn't mean it's better.

So in general it's not a big deal, but if I have a toss up aluminum is the way to go.

Hmmm...

What about the 6061? Is that the kind of aluminum it is? What about integrated gussets? Double butted welds, etc?

I'm just trying to know what to look for in a good frame, so if I go to a bike shop later on and see one I like I can firmly say "I'll take this one" without question.

One major difference in material is rigidity. All specs being equal, Al is more rigid. This doesn't mean it's better.

That's actually wrong. The reason why aluminum frame bikes are stiffer is because of the shape or rather the diameter of the tubing. Steel actually has a higher elastic modulus than aluminum (around about three times as much) and thus for the same diameter and thickness will deflect less when subjected to the same force. However, bikes made of aluminum generally have larger diameter tubes. This greater effective cross-section means the structure will be more rigid. The reason for this is twofolds.


Stiffness - A small diameter aluminum bike is very noodily. Ask anyone who's ridden early aluminum road bikes or anyone who's ridden one of the Trek aluminum MTBs from the early 1990s. Increasing the size of the aluminum tubes makes the structure as a whole much stiffer. This was the hallmark of big-tube aluminum frames as popularised by Cannondale and Klein.
Lifespan - Aluminum unlike steel has no endurance or fatigue limit. This means that unlike steel which will plateau at a certain fatigue strength when cycled a certain number of times, aluminum's fatigue strength will continue to decline the more it's cycled. Once you hit steel's endurance limit, you can continue to cycle the material at or below that load with impunity... forever. With aluminum, it will eventually fail because at some point the S-N (stress to cycle) curve dictates that the material can no longer support any cycles regardless of load. The answer to this is to design the structure in such a manner that it is extremely stiff and thus will never see a load high enough to cause a failure within a respectable lifetime. One way to keep the loads low is to use large cross-sections or effective cross-sections of material.

Khuon, I'm sorry... I lost you somewhere in your response.

Bottom line: If I were to buy a new frame, what would you suggest? And what features on a frame regardless of the kind of metal should I look out for? (as far as weld quality, etc).

Khuon, I'm sorry... I lost you somewhere in your response.

Bottom line: If I were to buy a new frame, what would you suggest? And what features on a frame regardless of the kind of metal should I look out for? (as far as weld quality, etc).

There's too many variables for me to give a single answer. It all depends on your criteria. Each frame material has its pros and cons. What are you looking for specifically in a frame. Additionally, the material is generally immaterial. The construction and design matter most.

There's too many variables for me to give a single answer. It all depends on your criteria. Each frame material has its pros and cons. What are you looking for specifically in a frame. Additionally, the material is generally immaterial. The construction and design matter most.

I just want something that will last a good long time, but most importantly be able to support a few hard hits if I decide to take it on some heavier trails. I'm not going to be doing any 10 foot jumps but I woulnd't mind hitting a few hard logs or rocks too.

Something that just has good overall functionality.

Please don't take offense but I would suggest you not try to engineer the bike yourself. That is to say that you should concern yourself with the ride quality, fit and usage parameters that the manufacturers and thus the designers have specified. Trust in the bike designers to have done their job in picking the right materials and determining the right design and geometry. Generally speaking if you use the bike within its intended scope of application then you should be okay. In general, most people will tell you that aluminum bikes are designed with a lifespan to be ridden hard (at their design limits) for anywhere between three to five years. If you're not being especially harsh on the bike then it will last longer. Steel bikes usually last a little longer. That said, I've seen MTBs of both steel as well as aluminum that are well over 10 years old that have seen extensive trail time. I've also seen bikes of both materials last no more than a couple of months. The durability and longevity is less a function of material and more of overall design and use/care.

Please don't take offense but I would suggest you not try to engineer the bike yourself. That is to say that you should concern yourself with the ride quality, fit and usage parameters that the manufacturers and thus the designers have specified. Trust in the bike designers to have done their job in picking the right materials and determining the right design and geometry. Generally speaking if you use the bike within its intended scope of application then you should be okay. In general, most people will tell you that aluminum bikes are designed with a lifespan to be ridden hard (at their design limits) for anywhere between three to five years. If you're not being especially harsh on the bike then it will last longer. Steel bikes usually last a little longer. That said, I've seen MTBs of both steel as well as aluminum that are well over 10 years old that have seen extensive trail time. I've also seen bikes of both materials last no more than a couple of months. The durability and longevity is less a function of material and more of overall design and use/care.

I understand. I'm just trying to understand frames more so I know what to look for IF I'd get a new frame. I don't plan on getting a new frame, but hell if mine cracks in half then I want to go to the bike shop and be able to pick one up. It's just I don't understand the difference from one to another, that's all I'm trying to do is to be able to decifier what's suitable for me, what materials work better for me, etc etc etc.

I'm sticking with my frame until it dies. But when/if that time comes, I just want to have enough knowledge to do the deciding on my own. :)

Lifespan - Aluminum unlike steel has no endurance or fatigue limit. .

May want to double check how you phrase that.

May want to double check how you phrase that.

Hmmm... what's wrong with how it's phrased?

I'm wondering the same thing. You pretty much explained the definitions 4.0

That's actually wrong.
I know about Young's Modulus too.


Steel actually has a higher elastic modulus than aluminum (around about three times as much)
...and weighs nearly 3 times as much

Hmmm... what's wrong with how it's phrased?
Aluminum does have an initial rated endurance and fatigue life, the rest is dead on.
I watch those Engineering Disaster shows on the History Channel and I've seen the Airline Metal Fatigue one a dozen time or more so I know that AL is rated

Aluminum does have an initial rated endurance and fatigue life, the rest is dead on.

It has a rated endurance and fatigue life but it does not actually have an endurance and fatigue limit. The curve just keeps dropping unlike with steel which plateaus at a certain fatigue strength after a certain number of cycles. For purposes of designing an aluminum structure, the fatigue strength and endurance limit is "effectively considered" to be at 500 million cycles which is to say that those values are taken into account when a structure is designed. Thus a conservative design will try to limit the loads on the structure to that less than the fatigue strength of the material at 500 million cycles.

It has a rated endurance and fatigue life but it does not actually have an endurance and fatigue limit.
See that's what I was having an issue with, the whole "limit vs. life" bit can be a touch confusing for some and I wanted you to clarify a bit. Aluminum also has load stress limits just like steel and pound for pound steel is generally stronger.

You know your stuff Khoun (especially when it comes to computers and planes ;) ) I just want you to expound a bit

I'm a little confused.

What the hell is a fatigue limit? If my bike reaches that, does it just explode or something? :D

That's actually wrong. The reason why aluminum frame bikes are stiffer is because of the shape or rather the diameter of the tubing. Steel actually has a higher elastic modulus than aluminum (around about three times as much) and thus for the same diameter and thickness will deflect less when subjected to the same force. However, bikes made of aluminum generally have larger diameter tubes. This greater effective cross-section means the structure will be more rigid. The reason for this is twofolds.


Stiffness - A small diameter aluminum bike is very noodily. Ask anyone who's ridden early aluminum road bikes or anyone who's ridden one of the Trek aluminum MTBs from the early 1990s. Increasing the size of the aluminum tubes makes the structure as a whole much stiffer. This was the hallmark of big-tube aluminum frames as popularised by Cannondale and Klein.
Lifespan - Aluminum unlike steel has no endurance or fatigue limit. This means that unlike steel which will plateau at a certain fatigue strength when cycled a certain number of times, aluminum's fatigue strength will continue to decline the more it's cycled. Once you hit steel's endurance limit, you can continue to cycle the material at or below that load with impunity... forever. With aluminum, it will eventually fail because at some point the S-N (stress to cycle) curve dictates that the material can no longer support any cycles regardless of load. The answer to this is to design the structure in such a manner that it is extremely stiff and thus will never see a load high enough to cause a failure within a respectable lifetime. One way to keep the loads low is to use large cross-sections or effective cross-sections of material.



khuon you're making me miss my materials science and machine design classes. Good times.

I'm a little confused.

What the hell is a fatigue limit? If my bike reaches that, does it just explode or something? :D

Do you know the scene in the Blues Brothers when they park the car for the last time? Its sort of like that. Try to be off the bike when it happens :D

Do you know the scene in the Blues Brothers when they park the car for the last time? Its sort of like that. Try to be off the bike when it happens :D

I've never seen the Blues Brothers...................

That's actually wrong. The reason why aluminum frame bikes are stiffer is because of the shape or rather the diameter of the tubing. Steel actually has a higher elastic modulus than aluminum (around about three times as much) and thus for the same diameter and thickness will deflect less when subjected to the same force. However, bikes made of aluminum generally have larger diameter tubes. This greater effective cross-section means the structure will be more rigid. The reason for this is twofolds.


Stiffness - A small diameter aluminum bike is very noodily. Ask anyone who's ridden early aluminum road bikes or anyone who's ridden one of the Trek aluminum MTBs from the early 1990s. Increasing the size of the aluminum tubes makes the structure as a whole much stiffer. This was the hallmark of big-tube aluminum frames as popularised by Cannondale and Klein.
Lifespan - Aluminum unlike steel has no endurance or fatigue limit. This means that unlike steel which will plateau at a certain fatigue strength when cycled a certain number of times, aluminum's fatigue strength will continue to decline the more it's cycled. Once you hit steel's endurance limit, you can continue to cycle the material at or below that load with impunity... forever. With aluminum, it will eventually fail because at some point the S-N (stress to cycle) curve dictates that the material can no longer support any cycles regardless of load. The answer to this is to design the structure in such a manner that it is extremely stiff and thus will never see a load high enough to cause a failure within a respectable lifetime. One way to keep the loads low is to use large cross-sections or effective cross-sections of material.

Okay Mr. Wizard...I didn't realize everything had to be perfectly scientific on this site, but I'll keep that in mind before I let my fingers start pecking next time. :D I was simply trying to give Roasted a very "lay" answer. Fact is, Al frames are usually more rigid.

Okay Mr. Wizard...I didn't realize everything had to be perfectly scientific on this site, but I'll keep that in mind before I let my fingers start pecking next time. :D I was simply trying to give Roasted a very "lay" answer. Fact is, Al frames are usually more rigid.

Hey! Thanks. That's a little more blunt and understandable from my point of view. :D

What are the differences between butting and gusseting? I had a welding class in high school but I think that was on a higher league than what we learned because it doesn't sound familiar.

Hey! Thanks. That's a little more blunt and understandable from my point of view. :D

What are the differences between butting and gusseting? I had a welding class in high school but I think that was on a higher league than what we learned because it doesn't sound familiar.
Well, I'll attempt this....but I am not a fabricator.

butting-- varying wall thickness to accomadate different stresses

gusseting-- extra material added at joints for reinforcement

I think that is about right

Yep. A butt is more subtle.. it's an increase in the thickness of the tube at a certain point, either on the inside (you can't see it) or the outside (you can see it if you look really carefully). A gusset is a sort of jerry rigged butt, achieved by welding a hunk of extra material to the tube. Some frame builders like Yeti pride themselves on not using gussets and instead using (expensive) custom butted tubing, but on most less expensive bikes, you'll see both gussets and butts.

As the steel vs aluminum question, to put it simply, aluminum frames tend to be stiffer than steel. This means that the frame will usually have a harsher ride, but won't flex much laterally (side to side) either. If you're big, heavy, and powerful, you might like this. If you're not, steel will be plenty stiff and will be more pleasant to ride on.

Aluminum isn't as strong as steel, and therefore the frames tend to be built using more material and larger tubes (which explains the stiffness). A good steel frame will last longer than a good aluminum frame, but a good aluminum frame should last for years anyway, if you don't abuse it.

Good aluminum frames tend to be just a little bit lighter than good steel frames, but not by that much.


Personally (and this is just my opinion), if i was getting a hardtail, i would prefer a steel bike, but if i was going for full suspension, aluminum makes more sense since it's a little lighter and the suspension system would determine the ride quality much more than the frame material.

You see many more aluminum bikes than steel ones in the mid-quality range mainly because it's trendy right now, and everyone understands '1 lb lighter', but not many people understand 'sweet riding characteristics', so the big bicycle conglomerates spec aluminum frames.

Good titanium frames combine the feel of steel with the weight of aluminum (or better), but they cost a big chunk of change.

Yep. A butt is more subtle.. it's an increase in the thickness of the tube at a certain point, either on the inside (you can't see it) or the outside (you can see it if you look really carefully). A gusset is a sort of jerry rigged butt, achieved by welding a hunk of extra material to the tube. Some frame builders like Yeti pride themselves on not using gussets and instead using (expensive) custom butted tubing, but on most less expensive bikes, you'll see both gussets and butts.

As the steel vs aluminum question, to put it simply, aluminum frames tend to be stiffer than steel. This means that the frame will usually have a harsher ride, but won't flex much laterally (side to side) either. If you're big, heavy, and powerful, you might like this. If you're not, steel will be plenty stiff and will be more pleasant to ride on.

Aluminum isn't as strong as steel, and therefore the frames tend to be built using more material and larger tubes (which explains the stiffness). A good steel frame will last longer than a good aluminum frame, but a good aluminum frame should last for years anyway, if you don't abuse it.

Good aluminum frames tend to be just a little bit lighter than good steel frames, but not by that much.


Personally (and this is just my opinion), if i was getting a hardtail, i would prefer a steel bike, but if i was going for full suspension, aluminum makes more sense since it's a little lighter and the suspension system would determine the ride quality much more than the frame material.

You see many more aluminum bikes than steel ones in the mid-quality range mainly because it's trendy right now, and everyone understands '1 lb lighter', but not many people understand 'sweet riding characteristics', so the big bicycle conglomerates spec aluminum frames.

Good titanium frames combine the feel of steel with the weight of aluminum (or better), but they cost a big chunk of change.
Good post

I'm a little confused.

What the hell is a fatigue limit? If my bike reaches that, does it just explode or something? :D

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.

I've never seen the Blues Brothers...................
What the heck is WRONG with you? :eek:
That movie is a classic must see movie! Next you'll tell me you've never seen The Rocky Horror Picture Show, or Labyrinth, or the friggen Goonies!

Frightening ::eek: :D