Empire bikes

Author Message
flag fishizzle
Posted: Nov 5, 2007 at 9:04 Quote
r-m-r wrote:
Torsional stiffness is very important to how solid a bike feels. The loading is a lot less than the in-plane loading, but it's still a real concern.

It's true that eliminating welds is a good thing, but drawn and cold-worked tubes are a lot better than cast metal. I'm not sure how those two factors offset one another.

I thought about it now and i think i have some ideas how it counters these problems.
First of all the I beams are both arched which is going to improve there stiffness in vertical planes which of course relates to torsional forces. Secondly surely by having two I beams any torsional forces will try to force the I beams upwards or downwards as they resist being twisted over each other which is a plane in which they have improved strength.

You mentioned the cold worked tubes, I take it you mean this creates better grain uniformity. Empire mentioned the frames are heat treated for something ridiculous like 2 days. After all the way this frame is made is the same as components like the landing gear are on jumbo jets etc. This stuff can take the abuse. When was the last time you saw something like that made of welded tubes?
flag frdh
Posted: Nov 5, 2007 at 9:22 Quote
fishizzle wrote:
r-m-r wrote:
Torsional stiffness is very important to how solid a bike feels. The loading is a lot less than the in-plane loading, but it's still a real concern.

It's true that eliminating welds is a good thing, but drawn and cold-worked tubes are a lot better than cast metal. I'm not sure how those two factors offset one another.

I thought about it now and i think i have some ideas how it counters these problems.
First of all the I beams are both arched which is going to improve there stiffness in vertical planes which of course relates to torsional forces. Secondly surely by having two I beams any torsional forces will try to force the I beams upwards or downwards as they resist being twisted over each other which is a plane in which they have improved strength.

You mentioned the cold worked tubes, I take it you mean this creates better grain uniformity. Empire mentioned the frames are heat treated for something ridiculous like 2 days. After all the way this frame is made is the same as components like the landing gear are on jumbo jets etc. This stuff can take the abuse. When was the last time you saw something like that made of welded tubes?
yeah I saw an article on them a while ago, it told about how they had a hard time finding a place that would cast their frame for them because they were such a small company compaired to all of the airline manufacturers that have landing gear cast in the same way the bike is. Its gonna be sick when it comes out, kinda looks like the Honda gcross frame..
flag pbuser16709
Posted: Nov 5, 2007 at 16:37 Quote
fishizzle wrote:
r-m-r wrote:
Torsional stiffness is very important to how solid a bike feels. The loading is a lot less than the in-plane loading, but it's still a real concern.

It's true that eliminating welds is a good thing, but drawn and cold-worked tubes are a lot better than cast metal. I'm not sure how those two factors offset one another.

I thought about it now and i think i have some ideas how it counters these problems.
First of all the I beams are both arched which is going to improve there stiffness in vertical planes which of course relates to torsional forces. Secondly surely by having two I beams any torsional forces will try to force the I beams upwards or downwards as they resist being twisted over each other which is a plane in which they have improved strength.

You mentioned the cold worked tubes, I take it you mean this creates better grain uniformity. Empire mentioned the frames are heat treated for something ridiculous like 2 days. After all the way this frame is made is the same as components like the landing gear are on jumbo jets etc. This stuff can take the abuse. When was the last time you saw something like that made of welded tubes?

There are many differences between airplane landing gear and bike frames. That may or may not be a good analogy.

Now, you say:

"...going to improve there stiffness in vertical planes which of course relates to torsional forces"

I don't know how to say this nicely, but that statment shows a lack of understanding of mechanics. Better than most, of course, but a little knowledge is a dangerous thing, as the saying goes. In-plane and torsional stiffness are not related and it's confusing to start casually associating the terms "force" and "stiffness".

None of us know the properties of the material and none of us know the strength or stiffness of this bike. The only statements I'm making are:

1. The I-beam is the best cross-section for in-plane loads, but it is not an ideal shape for torsional loads. It is possible that the design has taken all properties into account and has resulted in good strength and stiffness in all loading scenarios at a reasonable weight, I'm just concerned about the use of a shape that's not usually ideal for torsional loads.

2. Casting generally results in metal that is not as strong as drawn tubes of the same material. On the other hand, it can be used with non-weldable alloys and casting eliminates local brittleness around welds, which could offset the negative aspects of casting. None of us know the details on that and I'd even be hesitant to believe information from the manufacturer because they are certainly not an unbiased source.
flag fishizzle
Posted: Nov 5, 2007 at 17:16 Quote
yeah cause although its an I beam its an arched I beam so you have to treat it differently. Torsion after all is simple twisting forces(don't know why you can't see the relation, you said an I beam takes loads well in single planes which is true, but an arched I beam must be different as it starts at one angle and goes through into another angle. That means the I beam resists forces through all those planes, thus it is a lot stiffer then a regular I beam non?

They other point i was making is essential for any side loads to cause torsion the I beams would have to move sideways which surely is another plan in which they are very stiff.

Are bike frames a lot more different to landing gear? they have wheels,suspension and carry a load. Its seems quite relative to me. You've got little argument when this technology is being employed by all the big motorcycle brands.
flag pbuser16709
Posted: Nov 5, 2007 at 17:25 Quote
fishizzle wrote:
yeah cause although its an I beam its an arched I beam so you have to treat it differently. Torsion after all is simple twisting forces(don't know why you can't see the relation, you said an I beam takes loads well in single planes which is true, but an arched I beam must be different as it starts at one angle and goes through into another angle. That means the I beam resists forces through all those planes, thus it is a lot stiffer then a regular I beam non?

Non.

fishizzle wrote:
They other point i was making is essential for any side loads to cause torsion the I beams would have to move sideways which surely is another plan in which they are very stiff.

Torsion and lateral bending are different. Non again.

fishizzle wrote:
Are bike frames a lot more different to landing gear? they have wheels,suspension and carry a load. Its seems quite relative to me. You've got little argument when this technology is being employed by all the big motorcycle brands.

The same is true of deep-sea fishing reels. Non again.

A little knowledge is a dangerous thing.
flag potvinwannab
Posted: Nov 5, 2007 at 20:42 Quote
i doubt torsional stiffness will be an issue with this much metal. A forged design would be stronger (for what reason, i dont know) but the way i see it i feel my bike would be alot stronger if i filled all the tubes with pure metal (yes i know the weight would be tremendous but technically it would be stronger). Its like riding a giant crank arm, with wheels and a shock and what not. Especially no welds to screw up and crack. Althought once again, i would have liked to see a forged frame-as hard as it may be.
flag aniyn
Posted: Nov 5, 2007 at 20:49 Quote
You'd think a cast frame would be quite cheap, since you don't need welders and pipe benders and whatnot, but $4000? Seems like an awful lot to me.
flag pbuser16709
Posted: Nov 5, 2007 at 22:19 Quote
potvinwannab wrote:
i doubt torsional stiffness will be an issue with this much metal. A forged design would be stronger (for what reason, i dont know) but the way i see it i feel my bike would be alot stronger if i filled all the tubes with pure metal (yes i know the weight would be tremendous but technically it would be stronger). Its like riding a giant crank arm, with wheels and a shock and what not. Especially no welds to screw up and crack. Althought once again, i would have liked to see a forged frame-as hard as it may be.

Forging does good things to the grain structure in the metal. We'll leave it at that.

I agree with you that a forged frame has serious potential. It's still all but impossible to do hollow shapes, though (even more so with forging).

You're right that it's not at all difficult to make a frame strong. Ignoring suspension function and just looking at strength and stiffness, the definition of design optimization is to do more (strength, stiffness, durability) with less (mass). Any monkey could make strong frame if there's no weight restriction; it takes considerable knowledge and smart application of that knowledge to make a good frame without resorting to using excess metal.

Factoring in price, you can build a good frame with expensive materials and simple construction techniques or less expensive materials and more expensive construction. Once again, it wouldn't take much engineering talent to make a strong frame if you used exotic materials and NASA-grade construction techniques with some clumsy design.

So, that brings us back where we started: Is casting a good way to make a frame? I have no idea and neither does anyone else! I'll just restate my concern that the I-beam isn't an optimal shape for torsional loads and I'd be interested to see how that frame compares to some of the best tubular frames.

aniyn wrote:
You'd think a cast frame would be quite cheap, since you don't need welders and pipe benders and whatnot, but $4000? Seems like an awful lot to me.

Well, casting can be cheap, but some casting processes are better than other others. Similarly, you can get welded, tubular lawn furniture for twenty bucks, but it's not quite the same level of stuff as you'll find in a $4000 titanium road frame.

Also, casting involves expensive molds, so it gets cheaper (per item produced) at high production volumes. A large part of the costs of low-volume molded items are the molds.
flag fishizzle
Posted: Nov 6, 2007 at 10:51 Quote
I think your thinking too laterally.
flag pbuser16709
Posted: Nov 6, 2007 at 12:16 Quote
fishizzle wrote:
I think your thinking too laterally.

umm...what?
flag fishizzle
Posted: Nov 7, 2007 at 18:23 Quote
r-m-r wrote:
fishizzle wrote:
I think your thinking too laterally.

umm...what?

Well its really simple If I beams are stiff in the vertical and horizontal planes then two I beams together are stiff torsionally because they resist moving when the frame twists, as for any torsion to occur between the front and rear of the frame would cause the I beams to distort upwards and sideways.
flag pbuser16709
Posted: Nov 8, 2007 at 6:44 Quote
fishizzle wrote:
r-m-r wrote:
fishizzle wrote:
I think your thinking too laterally.

umm...what?

Well its really simple If I beams are stiff in the vertical and horizontal planes then two I beams together are stiff torsionally because they resist moving when the frame twists, as for any torsion to occur between the front and rear of the frame would cause the I beams to distort upwards and sideways.

Torsion is NOT the same as lateral motion. It causes a lateral deflection, sure, but they are NOT equivalent.

It's true that a few I-beams oriented in different directions will help stabilize the structure, but by that point, you'll have added so much metal that it would've been better to use a tube...hence my repeated statements that tubes are more efficient (MUCH more efficient) and handling torsional loads.

I-beams aren't bad at lateral loads, so their lack of torsional stiffness is NOT just a lack of lateral stiffness.

Let me say yet again: My concern is about torsional stiffness, not lateral stiffness and certainly not about in-plane stiffness. This bike might be the best bike in history, for all I know, I'm just saying the use of I-beams raises concerns that may or may not have been adequately addressed in the design.
flag ganga
Posted: Nov 8, 2007 at 7:10 Quote
i sat on the prototype one when i was in les gets this summer it seems super stiff, light and the geomitery is really nice if i could aford one i would get one.
flag pbuser16709
Posted: Nov 8, 2007 at 7:15 Quote
ganga wrote:
i sat on the prototype one when i was in les gets this summer it seems super stiff, light and the geomitery is really nice if i could aford one i would get one.

That's more than I've done, but I'm still going to wait until some more thorough reviews come in.
flag fishizzle
Posted: Nov 8, 2007 at 15:29 Quote
i really don't think bikes need that sort of torsional rigidity, but I suppose we'll see. It has to be said I've never seen a bicycle in history made of anything but tubes and most cars that still have chassis use box section. Theres no doubt this is a very strong bike in every other way. They base tested it with a weight of 20 stone dropping 3 metres without suspension and the rear swing arm has a safety factor of 5, so theres plenty of room to shed weight.

 


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