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Old 04-23-2004, 11:51 AM   #16
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The low rear roll is not so much to gain rear traction as it is to keep too much weight from being transferred to the front. The ultimate enemy in foam tire racing is the dreaded traction roll, which can be a result of too much weight getting transferred to the outside front of the car. When you run a lower rear roll center, you are transferring more weight to the rear of the car as you enter a corner, which will help to keep it on four wheels.

It is usually best to look at the front relative to the rear before looking at left to right; as many others have stated, when it comes to car handling, weight transfer is everything.
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Old 04-23-2004, 11:53 AM   #17
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Good point Shane. The bounce might even explain some of that "double steer" that happens on carpet. Stiffer shock oil should solve that problem though.

Ray- in reference to your last question- Unless I'm way off base here, the answer is yes, you are correct but not exactly for the reason you stated. I honestly believe it's different on different cars. So for your car (Pro 4?) it may be correct, but for another car that may have different camber rise for the same RC it would be different.

Example- last weekend I raced at Fernando's high traction asphalt track on foam tires. The TC3s could change the cornering balance of their cars with a simple upper camber link adjustment, but my EVO3S didn't respond to camberlink changes because the rear of the car was so STUCK! I did a rough comparison of the weight f-2-r balance compared to a fast TC3, and did everything I could think of to move my traction balance towrd the front of the car but nothing worked. I could make it worse, but never better. So my camberlink adjustments didn't affect the car the way they did on the TC3s. In fact, raising the rear upper link gave me more traction in ther rear, and raising the front upper link gave me more traction int eh rear!!! DAMMIT I was so frustrated~!!!!!
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Old 04-23-2004, 12:07 PM   #18
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i dont know the answer to weather he is right or wrong... but i have been oval racing for 17 years.. and sedan for 5 or so on and off... what i have learned from oval racing is that actual theory means very little from person to person...


in oval racing u can do everything one person says is the correct theory and get the exact opposite results for u...

menaing in theory it may be right .. but for each person it transfers different to the track.. has to do with diff cars, driving style. current setup ect....


u can go up to one pro and ask him his theory on an issue and he will give u one answer.. then u ask the next guy and he will say the exact opposite... but both guys are super fast and win just as many races and turn the same times....

so my point is is do it how u know to do it...weather it may be right or wrong... if it works for u then u have your answer.. if the opposite works for him... thats his answer...
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Old 04-23-2004, 12:28 PM   #19
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Quote:
so my point is is do it how u know to do it...weather it may be right or wrong... if it works for u then u have your answer.. if the opposite works for him... thats his answer...
Heres the deal-knowledge is power. And also-at a race when youve got no more practice and your in need of a set-up change-youve got to be fairly certain that the change your about to make to your car is going to work in the manner in which you think it will!!! This is when having theory and practicle knowledge become helpful.

There has got to be some universal truths to use in roll center tuning, regardless of rubber tires, small tires, foam tires, cap tires.
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Old 04-23-2004, 12:32 PM   #20
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When people argue with the science behind car setup, they are basically putting a spin on it, geared towards how they like a car to feel. If lowering a car's roll center makes it easier for you to drive, then why bother with the science? Learn what makes you fast and stick with it.

However, you can't argue with the science. All else being equal, it is known how a car will react to a specific change.

Like Ray said, knowledge is power! I may be a goofy driver, but I know and continue to learn as much about chassis dynamics as I possibly can.

Ray: I already posted the universal truths... Make sure you read the one about four posts up, as (I believe) it answers your question about why things are different on foam tires.
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Old 04-23-2004, 12:32 PM   #21
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And I dont mean the facts as learned from geometry.

I mean a simple fact that a higher roll center will always produce faster change in direction and a lower roll center will always indue more traction robbing chassis roll.

But-I guess thats just not going to happen. Too many variables included in every situation.
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Old 04-23-2004, 12:38 PM   #22
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Only thing I agree 100% so far is Shane's statement...

"weight transfer is everything"

By raising the upper inner pivot point, you lower the RC and this will allow for more chassis roll.


As a general statement: more roll = more traction

2 cents
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Old 04-23-2004, 01:02 PM   #23
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Old 04-23-2004, 03:01 PM   #24
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It's my opinion (which means little ) that the low roll center on carpet it utilized to reduce suspension jacking and hence traction rolling, eventhough I think a lower roll center creates more overall traction. The increase in traction can then be adjusted out via springs.
With a higher roll center the lateral forces of the tire pushing back on the car have more of an "upward" angle, which causes the suspension to "jack" or lift as the car corners.
I remember David Spashett mentioning that with a low roll center the car has a tendancy to "roll" the outside of the chassis into the ground during cornering. With a high roll center the car has more of a tendancy to try and pick up the inside edge of the chassis which eventually causes a traction roll, which is always a problem on carpet.
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Old 04-23-2004, 03:41 PM   #25
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somedays I think the saying "ignorance is bliss" is so true LOL

I just gave up on the theory and throw it on the car and try it out.
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Old 04-23-2004, 03:53 PM   #26
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Great thread. Who would have thought a thread with such a vague name/description could contain so much good info.

My question regarding rollcenters has to do with the different positions on the hub carrier. We'll use the TC3's rear hub as an example. Obviously the rollcenter is affected if you move the mounting position up or down but how about in towards the car or more outwards toward the wheel? Is that just to make adjustments as to how the wheel changes camber during the compression of the suspension or is there a rollcenter affect also?
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Old 04-23-2004, 03:57 PM   #27
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Rod,

The simplest answer is: the length of the camber link affects how much the roll center position changes with chassis movement. Once you go past that answer it gets really hairy
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Old 04-23-2004, 09:00 PM   #28
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wow. i finally got to read this article. and yeah, ray, there are many misleading statements made in that article. rather than write a thesis, i will opt to ask some very fundamental questions, and provide, hopefully, concise answers. formulate any thoughts that you like from them, up to and including the thought that talented drivers aren't always trustworthy sources of information or that i am in left field.

q1) at any given time, can the sum of all the downward forces on each tire ever be more than the vehicle weight? (neglecting drag/downforce effects)

a) no. so if lower roll centers transfer more weight to the outside, what happens to the inside? uh huh. that's easy, but not mentioned at all. this also applies to pitching moments.

q2) if, as the article states, we transfer more weight to the outside wheel, does that end of the car stay more planted?

a2) no. if we wanted to have a great difference in forces between the inside and outside wheels, we wouldn't strive for a low cg car. the very idea behind a low cg is to maintain, as best we can, the smallest difference in vertical forces between the inner and outer tires durring lateral weight transfer. if putting a larger force on the outer yielded more grip at that end, we would all be stiffening our front springs to get rid of push. that's nonsense, and we pay to read it. gee, i wonder why we are all so confused?

q3) does roll center affect the amount or magnitude of weight transfer?

a3) no. if your roll center was at the same height of the center of gravity, would there be no weight transfer? of course there would. the amount of transfer is governed only by the distance of the cg to the ground, the amount accelleration (be it linear or angular) and the relative distance spanning the wheels in the direction of transfer. for all practical purposes, let us consider the latter to be fixed.

q4) does more roll or pitch mean that more weight is being transferred?

a4) no, no, no. again, the amount of weight transferred is a function of the cg and the ground plane. and given the amount of pitch or roll in our cars, i challenge anyone to find proof that the change in cg due to pitch or roll is anything more than insignificant. if anything, the cg drops durring these motions, further disproving the idea that lots of movement is indicative of lots of weight transfer. what it should be telling you, is that it is taking a long time for the spings to fight it, all the while the chassis continues its movement. hence large displacements.

q5) do large droop settings allow more weight to transfer?

a5) ah, you guessed it. NO. for example durring hard decelleration as the chassis pitches forward, the rear lifts, right? it should. as it rises there is obviously less downward force being exerted by the rear tires. if not, the rear springs would not extend. 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. period. guess what? you just took a smooth transfer and caused the front tires to see a sudden spike in force.>>>now, to use an extreme case as an illustration to those who swear that it does. would a powerful monster truck fail to wheelie if you ran it with no droop in the front? no, but the wheels would lift faster than if you gave them some droop to maintain contact longer. get it?

if anyone who got to this point trusts my statements, you should come away with this: it is often not the amount of weight transfer that we are concerned with when we tune, but the time frame in which the transfer happens. this is not a minor technicality. it is huge. it is what dampening is all about. and i believe it to be the primary reason why advice is all over the place regardless of the caliber of the racer.

i don't claim to have all the answers. infact, it is obvious that i don't. and if you made it this far, you should be able to see that the above topics deal only in high school physics. that's pretty much mandatory to graduate these days, and it infuriates me to see publications with incorrect reasoning for a given phenomenon. i am not implying that what is seen on the track is not truly happening. just, please, come up with an explanation for it that doesn't condradict the works of newton and others more brilliant than most of us. that's your best bet if you intend to hold credibility among those on higher planes of thought. i guarantee those who get paid the big bucks in full scale have not done so by persuading people that newton hadn't a clue.

if you are in disagreement with my conclusions, please pick up a physics book, or choose to escalate it to a level that i have not arrived at so that i can learn from you as you disprove my statements.

i am not an antagonist. maybe an instigator, but definately someone who gets great satisfaction with understanding. and it really does pain me to see others who have the drive to learn being mislead, and worse yet, being stiffled by those who haven't the energy or the time to care.

i'm telling ya. the more intelligent discussion that takes place, the better off we'll all be. the best teachers can simplify complex ideas in amazing ways so that people of all levels can participate. on a board with 12,000+ users, i would be embarrassed to think that our community doesn't harbor a handful able to help out.

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Old 04-23-2004, 09:20 PM   #29
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^^ Post was very very helpful.
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Old 04-23-2004, 09:30 PM   #30
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Thank you seaball for that helpful insight.

SO, I'm coming away from that understanding that when you lower or raise your roll center, you change the speed of the weight transfer, not the magnitude. Correct?

This makes sense as to why lower rear roll centers on high bite tracks prevent lifting/traction rolling.
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