How light is too light

[gmdboston]

Originally posted by RandyO
ALL Other things being equal. yes I WILL START

OK, but just remember, you started it...lol

You are basing you statement on the equation F=MA ( force = mass x acceleration for the non mechanical types) and that is true, but the disscusion is about resultant damage in a motorcycle crash, not a steel ball impacting a concrete wall. Damage to a motorcycle is more dependant on the size, thickness, and choice of material, not just the total mass of the motorcycle. Lets look a typical crash where a bike hits stopped car in the passenger door at 20-30 mph.

Suzuki's SV 650 weighs about 435-440 wet and ready to ride. It comes with an aluminum frame and a 41 mm convetional fork. The frame is bolted to the engine in 6 locations. When these bike crash as stated above, they regularly bend or even break off the fork tubes at the lower clamp. The frames rarely bend, and the swing arms usually only twist a little and can esily be fixed.

Now take the same crash and substitute the GSXR for the SV. These bikes have 43 mm inverted forks (heavier than the SV's), and the motor bolts on in only 4 locations. The bike also weighs about 40-50 lbs less that the SV. In these same types of crashes the forks are less likely to bend, the triple clamps will be twisted beyond repair, and the frame will be bent in ( a steeper rake angle we call a "tuck under") and to the side. Also the lower steering head bearing race will be pushed up in the head stock casting and will lose it's press fit. Many times the plastics are still intact.

We used to cart wheel the old steel frame Honda CBR F2/F3 down the hill into the bowl at NHIS and just replace the handle bar and go. They weigh about 435 ready to race.

In these cases the lighter, stiffer chassis has sustained more damage than the heavier, more flexible chassis. This based on my observations over 12 years of chassis and suspension work on road, roadracing and dirt bikes, using a very sophisticated and accurite chassis measuring machine.

So back to your original statement, less mass=less inertia= less damage, is incorrect. Less mass = less inertia = less force, but not aways less damage.

[RandyO]

Like I said,ALL THINGS BEING EQUAL... not comparing a gsxr to a sv. they are not equal in construction

if the materals have the same sheer strength, compression strength, etc, ALL THINGS BEING EQUAL the lighter weight material will suffer less damage, lets compare apples to apples and oranges to oranges If you want to continue to compare apples to oranges, then you will get no arguement from me, they are beyond comparison

[richw]

Oboy happy turkey day

assume light is of equal strength then ok light is better.

i am talking to a bumer type like 5 mph tap should be zero dollars

and isn't inertia m (v x v) velocity squared

[TLRMan]

Originally posted by RandyO
Like I said,ALL THINGS BEING EQUAL... not comparing a gsxr to a sv. they are not equal in construction

if the materals have the same sheer strength, compression strength, etc, ALL THINGS BEING EQUAL the lighter weight material will suffer less damage, lets compare apples to apples and oranges to oranges If you want to continue to compare apples to oranges, then you will get no arguement from me, they are beyond comparison

Randy...you are thinking in 2 dimensions again.....

The angle of the dangle equals the square of the root.

Mass and velocity the same, it depends on where the frame takes the hit....too many structural equations to go thru, but a chain is only stronger at it's weakest link....So if one bike has beefier forks, the energy will be transmitted thru to the frame, and not hurt the forks whereas if the forks are lighter, they will take the brunt off the impact, and lessen the effects to the frame.

One other thing is how the engine is used as a "Stressed Member"...this also has a lot to do of what a frame is going to do if the bike gets binned....

But like Pete says, you have an infinate number of vectors you could go thru, and get different results...

[RandyO]

Mark...... apples to apples

2 different frames of same structural design but different materials, one lighter than the other

both get hit at same vector

the lighter one will get less damage.

isn't this whole discussion about making bikes with lighter weight materials? not about comparing bikes of different structural design

If you lighten a bike by changing it's structural design, then yes, it is very likey it will have more damage, but I don't compare apples to oranges

[TLRMan]

Originally posted by RandyO
Mark...... apples to apples

2 different frames of same structural design but different materials, one lighter than the other

both get hit at same vector

the lighter one will get less damage.

isn't this whole discussion about making bikes with lighter weight materials? not about comparing bikes of different structural design

If you lighten a bike by changing it's structural design, then yes, it is very likey it will have more damage, but I don't compare apples to oranges

2 different materials aren't apples to apples.....
What Pete said was that the Gixxer was lighter than the SV, but the gixxer sustained more damage...

Now, lets take 2 frames that are identical, one of CF, and the other of Alum. depending on how the lay of the CF is run, will determine how much strength the frame will have. Temperature of the frame is another issue. (we tried to make tuned 2 cycle pipes from CF).....anyhow....to make the CF frame as structually sound as the Alum, one would force you to have to change the diameters of the mounting bosses, and diameters of the CF. in other words, a lot more redesigning going on....so....if you could just cast a CF frame IDENTICAL to the Alum one, the CF frame would fail miserably.....Remember that America's Cup racer from Austrailia? Made of CF, was fine being driven in a straight away fashion, but when the angle got too great, it snapped the hull in half.

[gmdboston]

We can talk about differences in design and manufature all day and still differ in opinions. Lets stick to the original context of the thread. Bikes are being made lighter by reducing wall thicknesses of many parts, using less massive castings of stiffer yet more brittle materials, reducing the number of fasteners, new casting techniques that use less material (controlled flow if you've been reading the magazines), drilled bolts, titanium parts, improved welding processes, and a host of other weight reduction techniques. As the bike are getting lighter the components that take the brunt of the impacts, such as frames, wheels, forks and swing arms, are getting less and less capable of disapating the energy transmitted through them in a crash. The result is that even though the overall mass of the bike is reduced, the total number of parts and the amount of damage is increasing. This also has a direct correlation to repair costs.

I agree that if you take any object and drop it on the floor you get a certain amount of damage. How ever, if you make that same object lighter, and drop it from the same height, it will impact with the same velocity, and less force, but it may suffer more damage due to the decreased mass. In an impact the kenetic energy of the object is converted to heat, or light if it's velocity is high enough, the less massive object is less capable of disapating the energy to the atmospere, and more of the energy is disapated by deforming the object. The catch here is that motorcycles are not solid objects, and the weight reduction comes from making the structural parts smaller, thinner, and lighter.

If we look at your statement as it applies to the orginal context of the thread, as bikes get lighter will they sustain more damage, the answer is yes they will. Taking your statement to the extreme, I should be able to make a bike so light that I can run it into a wall, and it would sustain no damage. We know from real world experience this is not true.

Take the case of a solid steel ball hitting the ground from say 10 feet. When it hits the ground, it disapates the energy by getting a little warmer, but there is no noticable damage to the shape of the ball. Now reduce the mass by hollowing out the ball untill the wall thickness is say 0.0001 thick and drop it again from 10 feet. That ball will dent beyond repair suffering catasrtophic damage. You said "all things being equal", but the problem is all things can never be equal. To reduce the mass, we had to reduce the amount of material. We could say that a hollow ball is also a change in design, but so would internal bracing, honeycombing, or any thing other than a solid sphere. So that leaves a change in material as the only way to reduce mass and keep the same design, how ever we now have changed the structural integrity due to different material properties. The hollow ball hits the ground with much less force, but suffers more damage.

Motorcycles are no different, just far more complex than a simple steel ball. As engineers and designers make the bikes lighter, they are suffering more damage than the older, heavier machines.

If you want a bike to with stand the impact from a crash better, you will need to make them lighter AND stronger than they are now. The GSXR/SV comparison was an example of real world crashes, but I will tell you that the new GSXR's bend frames more easily than the old ones.

Less mass=less inertia=less force, is a true and quantitative statement.
Less mass= less inertia= less damage is incorrect and tries to combine the quantitative with the qualitative.

Damage can be defined as the number of parts deformed, the amount a particular parts is deformed, or the total cost of repair. To go further I'll ned to know your definition of damage.

[RandyO]

The problem here is you guys are talking about lightening the frames by compromising structural integrity, making thinnner walls using less material etc.

I am suggesting lightening the frames, engines etc by developing a lighter more exotic material that retains structural integrity...

what did I say in my previous post..... all things being equal... and specificly mentioning sheer strength, compression strength etc.

If you lighten the frame by compromising the structural integrity, it's a no brainer

[TLRMan]

Pete......
I'll meet you for a beer eh?

[highsider]

Originally posted by RandyO

I am suggesting lightening the frames, engines etc by developing a lighter more exotic material that retains structural integrity...

If you lighten the frame by compromising the structural integrity, it's a no brainer

What he said.

[Rye]

Originally posted by RandyO
less mass = less inertia = less damage

But not necessarily less cost!

[TLRMan]

Originally posted by RandyO
The problem here is you guys are talking about lightening the frames by compromising structural integrity, making thinnner walls using less material etc.

I am suggesting lightening the frames, engines etc by developing a lighter more exotic material that retains structural integrity...

what did I say in my previous post..... all things being equal... and specificly mentioning sheer strength, compression strength etc.

If you lighten the frame by compromising the structural integrity, it's a no brainer

Looks like you have to read what I wrote then....

....to make the CF frame as structually sound as the Alum, one would force you to have to change the diameters of the mounting bosses, and diameters of the CF. in other words, a lot more redesigning going on....

[Degsy]

No-one has thrown in the argument of how much cheaper frames have become.

I can get a brand new frame for my F4i for $700. If I paid the shop labor to replace it I would be looking at $a few hundred for that, but I can do it myself. Plus $150 or so to have Peter measure it (they come bent from the factory sometimes).

derek

[TLRMan]

Originally posted by Degsy
No-one has thrown in the argument of how much cheaper frames have become.

I can get a brand new frame for my F4i for $700. If I paid the shop labor to replace it I would be looking at $a few hundred for that, but I can do it myself. Plus $150 or so to have Peter measure it (they come bent from the factory sometimes).

derek

The best solution for all of this is plain and simple...

DON'T CRASH!

[gmdboston]

Originally posted by Degsy
No-one has thrown in the argument of how much cheaper frames have become.

I can get a brand new frame for my F4i for $700. If I paid the shop labor to replace it I would be looking at $a few hundred for that, but I can do it myself. Plus $150 or so to have Peter measure it (they come bent from the factory sometimes).

derek

GSXR frames are $2400 retail $1700 Dealer. most dealers charge 12-16 hours @ $75/hour for labor on the frame swap. Thats $3450 average cost.....for JUST the frame..... now add front wheel, plastics, forks...... hello Argo cycles,can I help you?

[Rye]

Originally posted by gmdboston
GSXR frames are $2400 retail $1700 Dealer. most dealers charge 12-16 hours @ $75/hour for labor on the frame swap. Thats $3450 average cost.....for JUST the frame..... now add front wheel, plastics, forks...... hello Argo cycles,can I help you?

Would there also be an issue with the frame being stamped? I thought new frames had no VIN...or is there race stock that has no stampings? I would have issue buying a bike with a frame that's been replaced if I couldn't get a resale the same as the oem. BTW Pete, you've got mail....

[brewmaster]

So in short that good old steel trelis frame maybe heavier but is more durable in a crash? Pete whats your opinion? I'm thinking track bike here, you know the drill. Durability would be a more important feature than absolute lightness.

I guess I'm going off on another tangent and or maybe I should turn this into a new thread. But IYHO what are the better track bike/am. racing choices based on durability?

[RandyO]

Originally posted by TLRMan
Looks like you have to read what I wrote then....

....to make the CF frame as structually sound as the Alum, one would force you to have to change the diameters of the mounting bosses, and diameters of the CF. in other words, a lot more redesigning going on....

Sure if you use carbon fibre.... but what about a new alloy of aluminum that hasn't been invented yet.... like "transparent"aluminum.....

My point is the answer to the post " How Light is too Light?" I don't think there is such a thing as "too light" ... are the alloy's that are used today the same as the alloys used a few years ago... NO, nor are the compsite materials, One of the reasons I support government spending in space is because of all the new metals and technologies that have come about, that wouldn't have otherwise... Have we achieved the ultimate technology yet.... not likely

[gmdboston]

Originally posted by brewmaster
So in short that good old steel trelis frame maybe heavier but is more durable in a crash? Pete whats your opinion? I'm thinking track bike here, you know the drill. Durability would be a more important feature than absolute lightness.

I guess I'm going off on another tangent and or maybe I should turn this into a new thread. But IYHO what are the better track bike/am. racing choices based on durability?

The best race or track bike is........some one elses!!!!!!!!!!
(see triumph....)

[bentbryan]

Originally posted by gmdboston
The best race or track bike is........some one elses!!!!!!!!!!
(see triumph....)

you mean the triumph hangin' in the tire wall right before T9?

[TLRMan]

Originally posted by RandyO
Sure if you use carbon fibre.... but what about a new alloy of aluminum that hasn't been invented yet.... like "transparent"aluminum.....

One of the reasons I support government spending in space is because of all the new metals and technologies that have come about, that wouldn't have otherwise... Have we achieved the ultimate technology yet.... not likely

Guess what I do for a living......

[RandyO]

Originally posted by TLRMan
Guess what I do for a living......

So, why haven't you invented transparent aluminum yet ?

[TLRMan]

Originally posted by RandyO
So, why haven't you invented transparent aluminum yet ?

You've been watching too many Star Trek movies....
But composites are a reality....I just do a lot of prototypes for Gen Dynamics, Mac Douglass, done a couple spaceflight packages for Nasa, and other stuff for MIT....Nothing that special..