crbrlfrost
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| posted on 27/6/06 at 05:45 PM |
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Actually, its quit simple Syd, unsprung weight is defined as all the mass that the coil spring has to react, which in the case of an inboard
suspension, also includes the same amount of the coil/damper assembly as normal (although since most dampers on an inboard suspension are monotube,
they can be oriented to take advatage of using the lighter, non-reservior end of the damper as unsprung), in addition to the linkage it has to react
force through to control the wheel. Is it not the spring that then has to push the bellcrank and in turn the pushrod to react force to the wheel?
Effectively you are adding mass between the A-arm and the end of the damper which all has to be controlled by the spring/damper. You can't look
at it as what is hanging off the dangly bits of the chassis. When the wheel is forced into bump or droop, the pushrod and bellcrank has a mass that is
accelerated just as the control arms and wheel hub assembly are. They are accelerated in direct relation to the spring/damper and not reacted directly
to the chassis. Thus, they are unsprung weight. The"Unsprung" weight is all masses that have to be reacted at the spring. The reason for
adding this weight is simply that the ends usually justify the means. Such as aero improvements on a race car (not just external,as is the case with a
formula car, but more room to flow air to the underfloor and brake/hubs in a sports racer), and better leverages on the damper (typical locost
probably see approximately .5-.7'' of travel at the damper of each 1'' of wheel travel rising rate, whereas a linkage can
provide 1:1 or even better). The bonus of a greater ratio is the fluid velocity in the damper. The greater the movement, the more fluid moves through
the piston causing easier tuning of the damper and less stiction per actuation. The other option to get the same amount of fluid flow on a typical
outdoor suspension is to increase the piston area, effectively making the outside of the damper larger and again reducing aero efficiency. As with
every other facet of engineering, designing a car is a compromise and the slightly added unsprung weight of an inboard suspension pays for itself in
other benefits. And as stated before, the ability to then shorten roll bars to react at the bellcranks or dampers instead out at the wheels will most
likely save enough weight that the mass of the overall system will probably be equivilant, the unsprung weight will almost always be higher. Cheers
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crbrlfrost
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| posted on 27/6/06 at 05:49 PM |
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PS, I may not have been at it for 20 years, but I also happen to make my living in engineering, and specifically automotive. And in all fairness, it
is a common misconception that inboard suspension reduces unsprung weight. But, I'm not smug, I'm opinionated but always willing to learn.
So if you'd like to get together and work out the physics, I'll bring the easel's. Cheers!
[Edited on 27/6/06 by crbrlfrost]
Oh, and just because I happen to be thinking about it, some very high end formula cars have managed to reduce unsprung weight slightly (although
whether it would be below outboard I don't know) by running their pushrod directly to the upright instead of the lower A-arm, which allowed them
to take the bending loads out of the A-arm and lighten it slightly, not to mention one less link between the wheel and the damper. Not that I would
recommend this to anyone as I haven't analysed the consequences. I would think you'd want it as close to the bottom of the hub as possible
to get the best angle, but it should also be inline with the steering axis to that steering movement wouldn't cause suspension binding. Oh well,
random ideas.
[Edited on 27/6/06 by crbrlfrost]
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Syd Bridge
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| posted on 27/6/06 at 06:21 PM |
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Trusty seppo...if you can't understand the simplicity, baffle 'em with bullsh1t.
No dynamics and fancy maths and arguments involved. You're confusing the simple weights involved with the dynamic situation. Two totally
different scenarios.
Weight and mass are simple things. Weight is mass under gravity. The weight of the coilover assembly is supported by the chassis and the wishbone,
equally, in a standard Locost. So is a (much lighter) pushrod. The spring also has to support the extra weight of the added mechanical linkages as
well. Otherwise, you'd be adding components, but not adding weight. Unobtainium, only available in the good ol'.....
When the coilover assembly is put inside the chassis, the weight of the coilover is then supported entirely by the chassis.
Therefore, the sprung weight is increased, and unsprung decreased. I think even the least educated on the forum can understand this.
It's really that simple.
If you have trouble with that, then you better go back to your books.
Cheers,
Syd. 
[Edited on 27/6/06 by Syd Bridge]
[Edited on 28/6/06 by Syd Bridge]
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JoelP
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| posted on 27/6/06 at 06:48 PM |
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what if you hung a 50kgs lump of lead on the end of the shocker syd? It doesnt matter if the shocker is inboard or outboard, for the wheel to move,
the lead must move. You could call it increased unsprung mass, but i dislike the term myself as it is an inaccurate description of what it commonly
represents. Im afraid that mr frost is correct here.
Unsprung mass in an outboard situation is commonly added up as the hubs, brakes callipers wheels tyres, half the wishbones, half the spring and the
mass of the part of the shocker that is moving. You could even pisss about adding up half the brake flexis and some fluid. This isnt quite accurate
anyway, as for the wheel to move 1 inch, the shocker might only compress half an inch, depending on angle and leverage ratio, so you cant add it all
up as equal. Likewise, its not the literal weight of the wheel as it hangs free, because in an inboard scenario some of the mass of the rocker would
be pulling in the opposite direction. Imagine trying to weigh a seesaw as it pivots. Maybe rotational inertia would be more accurate for comparisons,
but again, its not quite right. The only perfect way to compare two different setups would be to measure the inertia vertically at the wheel, ie,
apply a specific force and measure how fast it accelerates. You could then use this to calculate a mass for comparison, but the calculated mass
wouldnt equal the sum of the components exactly.
Anyway, its all a little bullshitty. The fact is, the man wants to build an inboard suspension system.
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Syd Bridge
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| posted on 27/6/06 at 07:24 PM |
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quote:
Originally posted by JoelP
what if you hung a 50kgs lump of lead on the end of the shocker syd?
Simple, the spring would still have to support the 50kg WEIGHT in an inboard situation.
In a standard locost, it would depend which end of the coilover assy it was put. At the topend, totally sprung weight; at the bottom, totally
unsprung.
JoelP...you like to have a pop at me whenever you can, so have a go at this.
(Firstly a liability waiver. Proper tools and lifting equipment must be used for any activity involving the lifting of cars and their parts. ) That
bit's for those who can't tell that a MacDonalds coffee is hot.
Support your chassis, then remove the springs. Only do this at the front, for now. (using the aforementioned lifting equipment) Lift the car, and
remove the under supports. Now, lower the lifting gear.
What has happened? The car has dropped to the floor!(Well, unless you've overtightened your 'crush' tubes. ) Which bits
didn't move? If you've got a normal locost, it's the outer hub/wheel/tyre assembly, and the half of the wishbones attached to the
uprights, and the bit of the coilover also attached to the wishbone outer.
This shows that everything but the bits that didn't move is supported by the springs. SPRUNG WEIGHT, wow, a truly mind blowing revelation.  (
It really is difficult to be serious about this very basic stuff. )
Now, do the same with an inboard setup. Which bits drop, and which dont?? The bits that drop are sprung weight, the bits that don't, err, well,
aren't.
In an inboard setup, what happens if you remove the pushrod? What holds the coilover assembly/bellcrank up? It's all attached to the chassis,
which is held up by the spring!!! Sprung mass. You can move it up and down with the pushrods detached from the wishbones.
Even the spring has to support at least half of its mass. Otherwise, where does its weight go?
Does it have to be explained any simpler????
Cheers,
Syd.
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Gav
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| posted on 27/6/06 at 07:39 PM |
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Wow, you mean you have actually been served something hot from macdonalds? now THAT is a revelation
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JoelP
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| posted on 27/6/06 at 07:42 PM |
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well syd, its not that i like having a 'pop' at you, but IMHO, you're wrong, and i do love arguing unfortunately. But then, so do
you 
It would seem that you accurately describe unsprung mass then, though i might add that if you remove the shocker in an inboard situation and do what
you suggest in your post, the rocker too will be pulled down by the wheel. Removing the push/pull rod is like removing the lower bracket in an
outboard situation.
However, i still say you are wrong because, when people talk about reducing unsprung mass, they are aiming to make the wheel move easier over bumps.
You are describing literal unsprung mass, which is a worthless concept - who cares if the wheel doesnt drop at all (ie zero unsprung mass) if there is
a bloody neutron star perfectly balanced on the rocker? The wheel wont move at all whatever you do.
To get the wheel to move easier over bumps, you want a low inertia, as i described on my last post.
Anyway, lets not fall out over this. We might even end up arguing about antisquat!
Love, Joel.
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JB
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| posted on 27/6/06 at 07:48 PM |
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Sprung and Unsprung
It seems you both have different interpretations of what unsprung weight is.
My understanding is.... all that is controlled by the spring / damper. So this includes the pushrods and rockers (or a proportion of).
In most cases an inboard set up increases unsprung weight due to the extra pushrod and rocker.
Suspension is all about compromise and I am willing to sacrifice extra unsprung weight for a 1:1 motion ratio by using a rocker suspension.
John
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JB
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| posted on 27/6/06 at 08:04 PM |
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Sprung Unsprung ......Google
I have just done a Google search on inboard suspension unsprung weight.............
Most say that you get a reduction in unsprung weight with an inboard suspension.....even the Porsche website.
HOWEVER I found a posting from a top Formula Student judge who concurs with my thinking.
"Dear Pat,I have been reading your tech introduction paper for beginner Formula SAE teams, and I think Idisagree with something you have
said.When you wrote about the virtues of mounting the shock absorbers inboard, one virtue youmentioned was a reduction in unsprung weight.I cannot
understand that, as I think that anything that moves when the wheel moves up and down isunsprung weight. In this case, the shocks would be unsprung
regardless of being mounted inboardor outboard.Am I wrong, or is there something I have failed to take into the equation. I look forward to
yourresponse.Regards(Name withheld by request)
Hi,Thanks for the feedback. You don’t know how good it feels to have proof that someone actually reads the stuff Iwrite.You are correct of course,
anything that moves with the wheel is unsprung, or a percentage is depending on thesuspension motion ratio.Having reread the article, I see I
was less than clear on that point. What was in my head at the time was thatwhen coil-over suspension units are mounted outboard, usually the damper
body end is mounted to thesuspension and therefore is ‘live’, whereas when the coil-over units are mounted inboard, usually the heavy end ismounted to
the chassis, and the lighter shaft end is ‘live’. This is why I wrote there is ‘usually a reduction inunsprung weight’.Of course, there is no reason
that outboard dampers cannot be mounted with the body end to the chassis, as longas these dampers are suitable for inverted use. I didn’t take into
account the unsprung weight of the actuating rodand the bell-crank, so all in all, there is probably very little saving in unsprung weight with
inboard mountedsuspension.Again, thanks for the feedback, and next time I revisit that document, I will correct it.RegardsPatTech Q & A – Pat
ClarkeFormula SAE-A Newsletter – Page 6August 2003
I have been a chief design judge so know Pat and he has good credentials.
I hope this clears up the argument.
John
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Syd Bridge
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| posted on 27/6/06 at 08:16 PM |
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Thank You for the kind u2u's, you know who you are. And to the dear gentleman with the suggestion re my head and anus; I would if I could bend
that far.
I just love it when people fail to grasp simple things, then resort to those blessed Staniforth books.
The best analogy of what is going on is a piston and conrod in an engine.
They whizz about at great speed exerting great force on the crank.....BUT...they still weigh something. They still have to be supported by something.
Otherwise, when the engine was running it would weigh less than when it was not. As the crank turns it has to push the piston up against its own
weight. As the piston comes down, it still exerts its own weight on the crank. Doesn't it??????
The confusion here is between simple weight(mass under gravity), and the dynamic forces when it all moves. Two completely separate sets of numbers.
Whilst one involves some of the other(and at my age a bit of 'the other' is a non-occurrence. ), the converse does not apply.
These foreigners do so like to get all unnecessary with themselves.
I wonder if Mummy will send him to bed with his boxing gloves on tonight?????
Cheers,
Syd.
[Edited on 28/6/06 by Syd Bridge]
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TheGecko
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| posted on 27/6/06 at 11:43 PM |
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quote:
Originally posted by Syd BridgeThe confusion here is between simple weight(mass), and the dynamic forces when it all moves. Two
completely separate sets of numbers.
Uhmmm....
Weight and mass are not the same thing! Perhaps the confusion here is the use of terms like "unsprung weight" when "unsprung
mass" would be more accurate. My understanding of this subject has always been that it is ONLY about the dynamic situation i.e. it's
about the inertial mass of the components NOT the gravitational mass (aka weight). Syd's example a few posts back seems to mix the two a bit,
to no-one's benefit.
quote:
These foreigners do so like to get all unnecessary with themselves.
I wonder if Mummy will send him to bed with his boxing gloves on tonight?????
This sort of pompous, Victorian, attitude (e.g. "Those
savages in the colonies have no idea, really" ) is quite amusing to the >99% of the world's population that live somewhere other than
the UK. Note: a sense of superiority is very often not accompanied by actual superiority.
Dominic
Brisbane, Australia
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crbrlfrost
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| posted on 28/6/06 at 01:19 AM |
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Thank you Joel, not for agreeing with me, but for not taking things on blind faith. Gecko, I realize mass and weight are not the same thing, but often
for these forums they are close enough for banter. Anyway, while driving around today, taking the 325 for a spin through the hills, I figured one of
the mental blocks for some might be the fact that in reality, the bellcrank's mass is (when static) completely supported by the chassis.
However, the moment it starts to move, and thus develope inertia, that force must now be reacted by the spring/damper and adds the the inertial
reaction caused by the acceleration of the unsprung "mass."
Sorry Syd, none of this is BS, but since I don't have a good picture, a 1000 words will have to do. As I said, I would be more than happy to
argue this out using math, but it might not go well on the forums. Besides, you don't have to take Stanifoth's or my word for it either,
you can gladly check out most engineering texts, VanValkenburg, Rowles or Milliken and Milliken. Cheers!
Ps, I thought you had more things you wanted to argue than just unsprung weight. Or are we to busy with this already?
Oh, sorry to interrupt again, but I had a thought. While we're raising and lowering cars for giggles lets analyse another scenario. We've
agreed that if you take the spring damper out of an outboard suspension, then the sprung mass falls to the ground. We've also agreed that if we
remove the pushrod from an inboard suspension, the mass again falls to the ground with the spring/damper removed from the system and thus part of the
sprung mass. But since we seem to be getting a little more technical these days, lets compare apples to apples. If we take the same inboard
suspension, and remove the spring/damper just as we did with the ouboard suspension, and leave the pushrod in place, what happens? The sprung mass
falls to the ground. Ooops, thats made to much sense.
[Edited on 28/6/06 by crbrlfrost]
[Edited on 28/6/06 by crbrlfrost]
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Syd Bridge
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| posted on 28/6/06 at 08:50 AM |
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Ok, I've been mixing mass and weight.
Try this....
Just take the spring out of any of the systems, what happens?
What falls towards the ground under its own 'weight', relies on the spring to hold it up. Sprung 'weight'.
'Weight' because it has gravity acting on it. All things have weight, so it can't be ignored, as you seem to be want to.
What doesn't fall, doesn't rely on the spring, so is 'unsprung weight'.
The bits that don't quite do either, are partially 'sprung weight' and partially 'unsprung weight'.
When it is all moving, we come into the realms of dynamics, where everything attached to the bit that finally pushes on the ground, is dynamic
'mass'. But note, this mass does not include the damper body(unless it moves and is not fixed to the chassis), and this 'mass'
still has to be supported statically, so exerts a 'weight' on something.
Just because it starts to move, doesn't mean it loses its 'weight'. eg. The bellcrank...When moving, it is still supported by the
pivot, so exerts its 'weight' on the pivot. It doesn't stop having 'weight', just because it starts moving!!! But, it
does start to exert more and different forces on the components it is attached to, due its momentum and thereby inertia.
You are failing to separate the static situation from the dynamic. The two are real, and separate, and different.
There, simple enough?
And I am personally well aware of the texts you quote, even one of the writers. None would disagree with what I have just put above.
Now you can go and have another look at your polar stuff.
Cheers,
Syd.
[Edited on 28/6/06 by Syd Bridge]
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Syd Bridge
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| posted on 28/6/06 at 09:12 AM |
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quote:
My understanding of this subject has always been that it is ONLY about the dynamic situation i.e. it's about the inertial mass of the
components NOT the gravitational mass (aka weight).
Everything exerts weight, and to ignore it is poor engineering indeed.
quote:
Note: a sense of superiority is very often not accompanied by actual superiority.
Who is that aimed at? You better watch out that a mirror doesn't suddenly appear in front of you.
Cheers,
Syd.
And I'm a true blue aussie passport carrier! And will be a lot closer to you than now in but a few short months. Sunshine, heat, sea breezes and
a warm sea. AHHH
[Edited on 28/6/06 by Syd Bridge]
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TheGecko
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| posted on 28/6/06 at 02:14 PM |
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quote:
Originally posted by Syd BridgeEverything exerts weight, and to ignore it is poor engineering indeed.
I'm not suggesting that the weight of components is meaningless but, in the context of sprung:unsprung mass ratios it might as well be, because
any attempts to maximise that ratio are in search of dynamic benefits, rather than static. It's about the ratio of the moving suspension mass
to the (hopefully) non-moving suspended mass (ie the chassis et al).
To return to the question, I believe that inboard suspension probably comes out about even with outboard for unsprung mass and a little more for
overall weight.
quote:
Who is that aimed at? You better watch out that a mirror doesn't suddenly appear in front of you.
Gee Syd, I thought it was pretty obvious that it was aimed at you and your "foreigners" remark, and the implication that, because someone
was from the USA and disagreeing with you he was a stupid wanker.
Re mirrors - I have no delusions of superiority over anyone
D
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crbrlfrost
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| posted on 28/6/06 at 03:44 PM |
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Well, frankly, I'm tired of beating a dead horse. It's gone from simple fact to symantics and without a specific system we can't
even argue exact masses. Ignornace must be bliss Syd. Anyway, I have a formula car and a prototype hybrid to attend to. And then, the coolest project
of all, a soapboxer for 4th of July. Fireworks, beer and gravity. Will the good life ever cease? Cheers guys!
[Edited on 28/6/06 by crbrlfrost]
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Syd Bridge
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| posted on 28/6/06 at 05:49 PM |
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All very sad really.
You see, I understand what you fellas are saying, what it's about, and know the subject area.
The sad thing is, you don't understand what I'm saying, don't seem to want to, and just keep saying I'm wrong. Without
understanding what I'm saying!
If it's not in the little that's in your books, it just don't exist. Thing is, the fellas that write the books and who are actively
working in the industry, rarely publish all they know. You get the rest at seminars and over a beer after a long testing and development session.
I'll leave you lot in your own little blissful worlds.
Cheers,
Syd.
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crbrlfrost
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| posted on 28/6/06 at 07:26 PM |
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Arrogance knows no bounds. I know exactly what you're saying and thoroughly disagree on the basis that I've done the computations, and
testing, and the modelling, and frankly, that has nothing to do with the books. I've also talked to many old race engineers, and the funny thing
is, is that even they disagree with each other. The obnoxious thing about your arguments is the lack of basis in the actual science of it and your
smugness. Frankly, I wouldn't want a lawn mower based on those priciples. But to each their own. On the matter of moment of inertia, that is
actually one topic where you are right. If the rest of the package is already optimized the relocation of the dampers can have a good effect, but
primarily in a small package (formule type car). Versus a Locost where the movement of the engine by an inch would have a far more drastic effect.
Anyway, go bury your head in the sand. Cheers
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JoelP
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| posted on 28/6/06 at 07:29 PM |
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just to get one thing straight syd, i have read no books on the subject, nor have i seen this subject on the internet. The stuff I posted, I actually
worked out myself, and it is quite simple. One minute you say we are wrong and the next, you agree its about inertia.
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crbrlfrost
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| posted on 28/6/06 at 08:08 PM |
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Darn Joel, you beat me to it. I was just going to say that if someone wanted to choose for themselves to simply do the sums. The accelerations are
easy to figure, the moments of inertia calcs can be found by anyone in a machinist handbook or statics book and the masses are easy to estimate. Happy
building/engineering. Cheers
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Syd Bridge
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| posted on 28/6/06 at 08:27 PM |
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No, No,NO,No,No. I will not continue!!
But this won't be the last post on this, as there's at least one person who can't be seen to be wrong.
Cheers all,
Syd.
You keep believing that stuff and my work will be secure for a long time.
[Edited on 29/6/06 by Syd Bridge]
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ChrisGamlin
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| posted on 30/6/06 at 08:37 PM |
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Rather than dropping either car to the ground to demonstrate, imagine holding the chassis still by bolting it to the floor and jacking up one wheel.
All the bits that move despite the chassis being bolted to the ground are unsprung or partially unsprung, all those that stay still are sprung.
Chris
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datz510
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| posted on 5/7/06 at 04:06 PM |
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Just an update.. I got both sides of the front suspension together with the new 2005 Yamaha R6 shocks and checked the wheel rates. The wheel rates
came out to right at 200lb/in at each wheel.
The suspension appears to work very well. I still have some fit and finish work to do (making spacers for all the heim joints), but for now, the
front suspension is good to go.
For all the naysayers: Many 
in your general
direction..
Only kidding...  
I know there will always be people that disagree with the way others build their cars. If we all did them only one way, it would make for a very
boring hobby, don't you think?
[Edited on 5/7/06 by datz510]
Hang on, we're goin for a ride!
1972 Datsun 510 (1600) w/ 200hp 3.0L V6
1995 Nissan Pathfinder rock crawler
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datz510
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| posted on 6/7/06 at 06:15 AM |
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Couple photos of the suspension. The car is sitting on the front suspension in these photos:
[Edited on 6/7/06 by datz510]
Hang on, we're goin for a ride!
1972 Datsun 510 (1600) w/ 200hp 3.0L V6
1995 Nissan Pathfinder rock crawler
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