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Old 04-23-2004, 09:35 PM   #31
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yeah dude. that is a big part of the equation. sudden changes are not usually what your chassis wants to see.

ever see a tamiya mini class run? we had some and the fast quys let the car roll like crazy. stiffen the springs with that small wheelbase and the RATE that the transfer occurs upsets the car so much that you can't keep it on it's wheels.
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Old 04-23-2004, 09:59 PM   #32
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how about this? (i'm still raging over here )

according to the article, low roll centers transfer more weight to the outside. i know i've already covered this, but check it.

i think even the pure empiricists (track only guys) would agree that high roll centers cause increased susceptability to traction rolling. traction rolling can only occur when 100% of the weight of the car is transferred to the outside. how then, do low roll centers cause more weight transfer (more than 100% ???), but less traction rolling?

gimme a break already. is someone gonna say that you can achieve 110% to play with if your roll center is low enough? arggghh.

man, i'm all riled up.
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Old 04-23-2004, 10:00 PM   #33
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Ok one thing that we have to take into account is that a "low" roll center and a "high" roll center is all relevant to the chassis at which they are used on and the suspension they use. I cant speak for Joel as Im not him but maybe just maybe he's thinking in reference to the Losi Street Weapon....might be one of the last cars he really raced so that's where I came up with that???? So on that car(the Street Weapon) the standard roll center would be considered "Low" to today's standards....as in its stock form it had a roll center point that was under ground level......now think about the time period when this car was made.....Sedans were raced on parking lots and that's about it maybe carpet here and there but not like today. Then Sedan racing gets more involved and tires advance and the grip levels get higher.....now with that SW in its stock form you could not get springs stiff enough to keep it from rolling with its LOW roll center. So what happens they RAISE the rear roll center and wow its not rolling as much. So there is not one way to look at how a roll center effects a car b/c there is many more variables at work.....and one cars LOW is another cars HIGH.....so whose right? Just look at most cars out there the XXXS High roll center is a lot higher then the TC3 standard roll center...which might be considered HIGH. This needs to be looked at a car by car and suspension by suspension basis. I know from my experience with a SW and a XXXS that the lower you make the rear roll center the more traction the car has and the faster it would change direction back and forth. And when the grip would get higher I would RAISE the rear roll center to stop traction rolls. So the way that I look at it Joel is correct.....but its all up to how and what your perceive as a "Low" and "High" roll center. These are just terms that are car specific.....like stated before a Losi XXXS high is not a TC3 High....so its not like a standard system can be used from car to car....you just need to understand whats going on and when making a change from one to another you know what it does to your car.
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Old 04-23-2004, 10:14 PM   #34
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Let me quote from J-"we all confused K"-MIBII

Anyways-Seaball-your amazing. I am proud to call you friend. Just wont admit it in polite society!!!

So-as this weekends racing approaches and our tracks level of grip is 50% of the Nats, I am inclined to raise my roll centers front and rear to achieve more mechanical grip.

But now it seems that I have been wrong all this last 6-months. Maybe it has worked for me at times-but not for the reasons I thought.

Also-KevinK-great point about relative termninology and I do agree that Joel put it in terms that I am sure he thought the average subscriber could ingest and keep down.

And it also seemed biased towards heavy Nitro sedans.

If Seaball wrote the article-theyd get 10,000 e-mails with the subject line:??????
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Old 04-23-2004, 10:14 PM   #35
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seaball, I'm tired and don't feel like disputing everything that needs discussion on your post, but I'll give you an example so you can do a little ciphering on your own ideas.

NHRA Super Stock classes. The front suspensions on these cars are usually very tunable but still in a stock "style" configuration. Almost all of them run suspension limiters on one or both front wheels. This does the same a our droop screws. The bolts or cables stop the suspension from extending at a set point. So why is it that we see these cars doing the huge wheelies for 100' after leaving the starting line when most good suspension tuners know that huge wheelies are a waste of forward energy and result in lowered E.T.'s? Simple- because if they don't get the full weight of the car on the rear wheels as the car comes into it's torque curve and begins to lay big power to the track it will simply blow the tires off. According to your theory there's no need for the wheel stand because all of the weight is on the rear tires when the car begins to accelerate. This is incorrect. You are assuming the tires will stay within their slip angle until full weight tranfer has occurred no matter how quickly that happens. If you fully limit the front suspension and don't allow weight transfer to happen gradually then the slip angle of the tires doesn't expand and you have a loss of traction. The trick is to get the weight to tranfer faster than the need for added traction while wasting as little energy as possible. That's where the limiters come into play. By setting the limit height you dictate how far the front springs assist in weight transfer before they fully load the rear suspension and begin to slow the upward movement of the front of the car. Take them off and the suspension assists in trasfer and upward motion all the way to full extension and the car gets over on the bumper.

All of your conlusions seem to assume the car can reach full weight transfer while staying within it's slip angle. If that were true we wouldn't need suspensions, we would just run flat pan cars.

In regards to your last traction rolling question- high roll centers lower the roll moment and thus decrease leverage of the CG over the RC and LESSEN the roll. You stated it backwards. But to further answer your question with the assumption of what you were trying to ask, raising the roll center (lowering the roll moment) decreaes the weight tranfer which makes the slip angle smaller and hopefully allows the tires to reach a point just over the slip angle where they begin to break traction right before the car tries to traction roll.
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Old 04-23-2004, 10:16 PM   #36
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the very problem is that our largest r/c magazine is treating what advice comes from the author as general statements. your right. and that is a problem. no kevin, not that you are right, but if his understanding comes only from a few cars. if he speaks from years of experience, i want to know what vehicles he speaks of so that i can disregard it if mine is not on the list. when the laws of physics come into play, your vehicle is never omitted from the list.

it did appear, however, to imply that high and low was relative to each car. meaning it doesn't matter what car you have! a lower roll center will do...etc. lower than you previously had on your vehicle. it made no mention of switching between vehicles as a tuning method of changing your roll center. the article presented the high and low connotations as relative to what you could achieve within the constraints of your vehicle. as a method of tuning.

yes, there are many things going on simultaneously when we are on the track. and the article did give that it's proper dues. what i am targeting are the very fundamentals that are essential to understanding. there are multiple statements written that, put bluntly, are just lies. not malicious or purposeful, but certainly speak toward a huge duality between driver skill and driver understanding. very dissappointing when those words fall on so many eyes.
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Old 04-23-2004, 10:26 PM   #37
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Seaball I see your point, but look at the article from a different point of view. I think we can safely say that only about 5% of the people that read that article know enough about suspension tuning to even attempt to argue it much less dispute it. Maybe another 20% have a knowlege of suspensions and can grasp the ideas easily. The other 75% have no idea what it says the first time they read it and must read it many times and ask questions or read other material to even understand the terminology. So if you were writing an article, would you direct the technicalities toward the 5% that fully understand it, or would you simplify and generalize to give the 75% a beginning point to learn about suspension tuning?

I mean, do you need to be told to clean and wash a body before painting on every issue of RCCA? No, but 50% of the people reading that article DO need to be told.
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Old 04-23-2004, 10:47 PM   #38
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Seaball...Like what Big Dogg said the article is geared more towards a newbie audience.....For the same reason that your local news paper or USA today is written at a 5th grade level...so everyone can read and understand it.

I have yet to read the article but Im sure that its not LIES its just printed in a way for most to get the concept of what does what. And Im sure that if you went and took your TC3 or what car it is that you drive and LOWER the rear roll center it will have more rear traction and then when the grip level gets higher it will flip....then raise it back up and it will stop flipping as easily.....and from what I have read in here is what most people are saying is wrong.....when its not the case.


Quote:
So-as this weekends racing approaches and our tracks level of grip is 50% of the Nats, I am inclined to raise my roll centers front and rear to achieve more mechanical grip.
Ray....are you talking about raising your roll center of your camber link location? B/c if you are thats the only way that you will have more mechanical grip and thats because of the camber change and the tire staying flatter and in contact with the ground. Now if you go and raise your roll centers for your lower A arms your car will less mechanical grip. Try it this weekend and see what happens.

Does it say in the article that Joel is talking about lower A Arm roll center and not the camber location roll center? This might be where some of us are getting confused about things. The Higher camber link roll center will have higher traction....and a lower one will have less....but this is effecting the camber change most of all.
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Old 04-23-2004, 11:07 PM   #39
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thanks ray, but i'm surely not. i think big dog would back me here. hey big dog. whattup?

i actually meant every word of what i said. i think you are reading, or perhaps inferring, things incorrectly.

firstly i never, in all of those words, talked about the roll moment. i have full understanding of the inverse proportionality that exists between the roll moment and the roll center height.

lowering the roll moment does not decrease the weight transfer! period. if the rc and cg were colinear (roll moment=0 and the car would not budge) the weight transfer would still be present in the exact same value it would in any normal roll center configuration. only this transfer would happen instantaneously as there would be no suspension to dampen the transfer over time. that's a big fundamental that can't be screwed up. for beginners or experts. it's ground work.

and you actually supported my conclusion on droop. the only way for all the of the weight to be on one side is if there is none on the other side. yes, that would define a wheel stand. my only point is supported by your example in that by allowing the droop to exist in large quantitites, you change the time that it takes to transfer whatever weight is going to transfer due to accelleration, and not the amount. umm, i can't believe that i would ever state, or imply, that all the force is on a particular end before any accelleration takes place. it is this very accelleration that creates the force transfer! weight transfer is proportional to accelleration. f=ma chapter two i'm guessing. it's easy... if you want f, you'd better have a non zero value for both m and a.

EDIT:
Quote:
what happens when your car is not done pitching forward, and the rear droop screws catch the chassis? the chassis motion suddenly takes the force that the rear tires had on the ground and lifts them, inturn adding what force it took from the rear to the front.
actually the above excerpt of mine does imply that all of the weight from the rear is transferred when the screws contact the chassis. i used poor terminology as to lift does imply "from the ground". i should have written - "chassis motion suddenly takes the force that the rear tires had on the ground and ACTS WITH A LIFTING FORCE on them. sorry, and thanks for pointing that out.

i dunno. i don't think we need anymore examples of unexplicable phenomenon. i think we need trustworthy answers for the much too many that already exist within our hobby.

lets focus our efforts in working together to put newton's findings with what our eyes are seeing. it's all happening just as he said it would, but we are failing to recognize alot of it. granted with these things being 1/10 size, we've got our work cut out for us. i consider it fun task. please help me and anyone interested.


i am not trying to be above and beyond anyone. i would have been fine reading general guidlines of what to do and when, with NO explanation of why. but to read some bogus stuff is just not cool to me. and i can agree that targeting beginners or novice is great. guys like us do just this to find the "extras".

but the guy responsible for this whole thread was baffled after what...4-5 years in this hobby and some good accomplishments as well? that's not good.

man, i'm not looking to make enemies with anyone. i just hate guessing.
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Old 04-23-2004, 11:08 PM   #40
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kevinK-I usually dont change the height of the camber links as much as I try long or short-but always in the higher row of holes (Tc3).

But now that I have the pro4-I am more incllined to try raising and lowering the ballstuds both inboard and outboard. I have tested and felt the remarkable changes from making the front and rear camber links longer and shorter!!!
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Old 04-23-2004, 11:29 PM   #41
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I think it's time for a reality check on some of this -- thank you, Kevin! -- and I can definitely sympathize with Joel, because I just wrote a similar article.

As a writer, you have 3-4 pages to summarize a very complex concept in a way that the average racer is going to understand. The average racer does not care WHY some of this stuff happens, they just want to know what some of these changes are going to do to their car.

That said, there are certainly more advanced topics to be discussed about roll center, but many of the ones mentioned here stray far from that topic and more into vehicle dynamics and other theories.

I will touch on one thing, however: it was mentioned that roll center does not change the amount of weight transferred, only the speed as which the weight is transferred. But, speed is not actually the correct term here -- roll center actually changes the amount of force that needs to be applied AT a particular point to get the chassis to roll TO a particular point. Thus the same force applied at the same point with two different roll centers will result in two different "amounts" of roll.

Depending on how you look at this, the statement "a lower roll center -- or more specifically, a larger roll moment -- will cause more weight to be transferred" can be both correct and incorrect.
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Old 04-24-2004, 06:48 AM   #42
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Default Wow! this is good!

Hey guys, I read the whole thread. I have been reaiding and expirmenting with roll centers for a long time.

This is what I have found the best info. It all makes sense to me.

A couple of MY thoughts.

Droop screws are by far the best way to stop traction roll. When the droop screws hit , the roll changes speed, or plain old stops happening because of the immediate change of weight and CG. With out the screws, the weight transfer keeps going until you roll.

Shock oil controls the speed of the body roll, Springs control the amount. You guys already know this.

Lowering the Roll Center gives it more leverage on the Center of gravity to make the car roll MORE. or at least want to.

http://users.pandora.be/elvo/

Please read this article, I had to print it and read it a hundred times.

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Old 04-24-2004, 09:29 AM   #43
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Changing the droop limiters will not necessarily stop or even slow down traction rolls. If you're close to traction rolling you can control it with droop.

The answer is on the previous page...Apply 5 pounds force to the bottom of an RC car and is will leave the ground. Apply 500 pounds force to the bottom of a race car and it will move a little and that's it.

We don't lower the rollcenter on carpet to control traction, we do it to controll the fact that the car wants to flip. If you look, the chassis (suspension) isn't rolling much when we "traction roll".
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Old 04-24-2004, 10:20 AM   #44
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well, i thought id mention something... as i read that article, i think he was talking about just the inner mounting. not actually moving the hingepin.
not that i have a clue about rollcenter, tho! i just want to know of my 415, if i remove spacers from the inner front link, will i get more traction, or less?!?!?! on asphalt, rubber tires, that is...
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Old 04-24-2004, 10:31 AM   #45
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Raising your roll center will give less roll moment which will make your car roll less. YOu want the car to remain flatter so it will slip the wheels instead of dig in and flip. This can also be done with stiffer springs, the car will roll less and you will have less chance of traction roll. Basically you are trying to loose some traction. HOW you do it is another thing. Roll bars can be of help too.

A lower center of gravity should help more than raising the roll center. The closer the two are, the flatteer the car should corner.

ONLY my thoughts.
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