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Old 12-24-06, 08:02 AM   #1
wheelhot
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Stainless Steel Mountain Bike and low center of gravity?

Heya, I was wondering what you guys think of a Mountain Bike which has a Stainless Steel frame? My dad told me that stainless steel if cut properly could be as light as aluminium, is this true? Because he want me to design my own Anthem Swingarm using stainless steel since he want me to learn about making product out of aluminium. Haha and since I love bicycle soo much he ask me to design some parts out of stainless steel.

My second question is why the lower your shock the lower the center of gravity? How could shock placement determine your point of gravity?
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Old 12-24-06, 08:09 AM   #2
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Originally Posted by wheelhot
My second question is why the lower your shock the lower the center of gravity? How could shock placement determine your point of gravity?
I feel that there is a lot left out here, where did you read/hear this? were they talking about just the weight of the shock, and it's effect on the center of gravity? were they talking about a specific bike? Give us more info please!
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Old 12-24-06, 09:09 AM   #3
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well, I remember reading about some bikes that because of the high pivot or shock placement like Blur it feels different when going downhill comparing to bikes with a lower pivot or shock placement like Giant Anthem. Im not sure if this fact is true though because a guy say that Giant Anthem feels more stable when going downhill then Giant NRS is because of the pivot/shock placement
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Old 12-24-06, 09:48 AM   #4
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Aermet steel, an *aerospace version* of stainless, has been used for some high-end frames. It was pretty hard to work with as a framebuilding material, hence it's very limited market share.
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Old 12-24-06, 11:00 AM   #5
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I'm going to put this in the category of not recommended. At least for you. Changing the shock mounting position can lower the bike's bottom bracket, thus lowering your center of gravity. When you make geometry changes like this, you're not just changing one variable, though. The head angle will also become slacker, affecting the bike's steering. If you're racing XC, you probably don't want a lower BB and slack head angle. I'm suggesting you do not attempt this for several reasons. 1) If you're asking here what the net effect will be, that's not a good sign that you know what you're getting into. 2) Forget about any warranty on your bike's frame if you ever break it. 3) Making it out of steel is going to add weight of the stock configuration which is taking away from your goal of making a faster XC bike.

Big question: Have you ridden your bike yet, and if so, what is wrong with it's current geometry?
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Old 12-24-06, 01:05 PM   #6
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Originally Posted by ghettocruiser
Aermet steel, an *aerospace version* of stainless, has been used for some high-end frames. It was pretty hard to work with as a framebuilding material, hence it's very limited market share.

Aermet isn't an aerospace version of stainless steel at all. I'm not sure where you heard that from, but they are wrong.

Aermet is an unusual, high hickel, high cobalt steel which is strengthened by a lot of cold work and very fine dispersion of stable carbides which makes it a pain in the bottom to machine or draw, which is why it is so difficult to use for framebuilding.
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Old 12-24-06, 01:52 PM   #7
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Go check out the frame building forum - Reynolds now has a stainless steel tube set for bikes.

And all other considerations aside, if your design has the linkage and/or shock lower in the frame, then OF COURSE your center of gravity will be lower. How much difference that makes to the way the bike handles is debatable. Designing a full-suspension bike, like a lot of design problems, is all about trying to optimize lots of conflicting variables. Try designing a full suspension bike that weighs under 20lbs, can withstand 10 foot drops onto flat surfaces, and costs less than $500. You can't do it, but all of us want light bikes that are also tough and cheap.
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Old 12-24-06, 02:00 PM   #8
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But only available in road tubesets for a while, Thor. Any other diameters won't be available, Reynolds tell me until late into next year.
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Old 12-24-06, 05:53 PM   #9
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Aluminum is just fine for mountain bikes. It's relatively cheap and the stiffness is not a detriment to the ride comfort due to the large tires and the suspension. It doesn't rust. There has to be an economic or performance benefit to another material and I don't see any for SS in an ATB .

Lower center of gravity generally means low ground clearance. It's not all that productive to hit your pedal on rocks and roots, so there is a lower limit. My 2003Speciaized FSR, designed for XC is about as low as I'd want to go.

Center of gravity is generally set by the bottom bracket height as when one is riding the rough stuff, he's on the pedals and most of the rider's weight is on the bottom bracket. The rider is "live weight" meaning the riders center of gravity moves due to the body English used to maneuver and stabilizes the bike in the rough stuff, turns and in the air. The height of the center of gravity is not all that important. it's more a function of how the rider moves his CG than the actual height.

My FSR is much faster in the turns, yet I sit higher than my old hardtail. It also has two positions for the lower shock bolt. By moving the the shock to the more rearward bolt position, I reduce the travel and the initial height by 15mm.

Al
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Old 12-24-06, 09:15 PM   #10
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Oic, well the swingarm project is for fun. My dad believes that since stainless steel is stronger then Aluminium, you can cut it to be thinner so its weight would be almost identical to aluminium. Oh yeah and im not planning to change its geometry, just redesign the swingarm without changing its pivots. Now time do research on aluminium bonding

And thanks for the tip about low centre gravity. Kinda get it
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Old 12-25-06, 03:31 PM   #11
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Originally Posted by Falanx
Aermet isn't an aerospace version of stainless steel at all. I'm not sure where you heard that from, but they are wrong.
Right you are. I put in in the quote as I half expected someone with a metallurgical agenda would call me on my bad terminology. I knew a guy who worked with it as a framebuilder back in the 90s, and eventually gave up due to the material being so hard to work with.
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Old 12-25-06, 03:41 PM   #12
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Originally Posted by wheelhot
Oic, well the swingarm project is for fun. My dad believes that since stainless steel is stronger then Aluminium, you can cut it to be thinner so its weight would be almost identical to aluminium. Oh yeah and im not planning to change its geometry, just redesign the swingarm without changing its pivots. Now time do research on aluminium bonding

And thanks for the tip about low centre gravity. Kinda get it
Irrespective of the material, you are lucky to have the opportunity to do this kind of work. Great learning experience and, you will gain a lot of usefull insight by experimentation. If nothing else, you can tailor the bike to what you like and change it as you progress.

Al
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Old 12-25-06, 05:33 PM   #13
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I would not do any thing to your Anthem, sence it is your primary bike (and a very sexy bike). If you have the being to build a FS bike with your swing arm on it! That would be an awsome thing to do! I have always wanted to build a bike from the ground up, but dont have the right stuff.

Good luck!
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Old 12-26-06, 12:03 AM   #14
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thanks , now I need to learn using AutoCAD professionally (that why my dad actually wants, he gives me this project so I can help him in the future )
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Old 12-26-06, 11:57 AM   #15
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hey we use CAD systems at school! Not very good, too much stuff to think about. I like the blue print and electrical stuff
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Old 12-26-06, 01:03 PM   #16
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Wheelhot, have you even had the chance to ENJOY the bike as it was meant to be? I understand the urge to learn about things but honestly you really should have just designed a new bike for yourself starting with paper and pencil. You will never be happy with this Anthem.
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