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Old 04-07-2004, 02:38 AM   #31
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Default Re: Re: meat for thought

Quote:
Originally posted by elvo

I'm an XRay factory driver, and I've played around with roll centers. IMHO, very, very similar results can be obtained withlong arms and a slightly more angled link. Maybe not exactly the same as short amrs, but very, very similar.
I owned a tb01 evo3 for a while and did alot of stuff like that with shimmimg upper and lower arms. Its amazing the difference a 1mm shim can make!

From all my rc expereince the most import part of your cars suspension setup is its rollcenters... far more important than any oil, spring or swaybar. Having the option of long or short arms on the x-rays will be an advantage for those who understand how to use it.
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Old 04-07-2004, 03:17 AM   #32
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Cole: no, pitch as in pitching motion. Fore-aft. Braking and accellerating.
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Old 04-07-2004, 03:20 AM   #33
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Quote:
Originally posted by elvo
Cole: no, pitch as in pitching motion. Fore-aft. Braking and accellerating.

Hmmm. Seems like I have to find a translator...
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Old 04-07-2004, 04:03 AM   #34
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Quote:
Originally posted by elvo
Cole: no, pitch as in pitching motion. Fore-aft. Braking and accellerating.
Just checked 3 translators, which use to be good.... But the closest I could get (there's many meaning of "pitch") is degree of slope...

It would be nice, if you can try explaining with another word?
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Old 04-07-2004, 04:07 AM   #35
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Hi Seaball,

Interesting topic, I like your way of thinking. I've often wonder about such tendencies, whether they were real or seat of the pants (not to use placebo effect).
One aspect of the differences that could be addressed is the dynamics of angular movement, I mean the acceleration of the moving parts about their pivots. I would think that if you calculate the inertia of a short arm system it will be much different then the long system one. In this comparison the short arm system could accelerate much more freely about it's pivot than the long one.

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Old 04-07-2004, 04:17 AM   #36
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Default Re: Re: meat for thought

I'm an XRay factory driver, and I've played around with roll centers. IMHO, very, very similar results can be obtained withlong arms and a slightly more angled link. Maybe not exactly the same as short amrs, but very, very similar. [/B][/QUOTE]

in other words, on the xray, long arms = more angled links, while short arms = flatter links?
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Old 04-07-2004, 04:36 AM   #37
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Alana - no, the other way around.

Cole - http://www.slams.freeserve.co.uk/Q&A...20Throttle.htm

There are 3 basic movements a chassis makes: roll (side to side), pitch (fore-aft), and yaw (like wiggling the tail)

FYI - there is a "roll center", but there's also a pitch center and a yaw center!
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Old 04-07-2004, 04:36 AM   #38
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oh yeah, Cole. Try google instead of a translator :-p
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Old 04-07-2004, 05:26 AM   #39
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Quote:
Originally posted by elvo
Cole - http://www.slams.freeserve.co.uk/Q&A...20Throttle.htm
Thanks, that cleared things up !
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Old 04-07-2004, 05:36 AM   #40
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Great post!

I'm still trying to understand all but keep them coming...

Btw... Anyone who can explain more about the effect of the length of the linkage/turnbuckles?
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Old 04-07-2004, 05:56 AM   #41
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Hi Peter

Here there's an explanation about length of camber lengths and angels. Go to "suspension" and eventually the section "Touring setup guide".
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Old 04-07-2004, 08:14 AM   #42
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Hey guys, I'm confussed about a few things that were said here....

#1 - The wheel is mounted to the axle in the hub correct? The hub is mounted to the suspension arm per hinge pin - the distance from the hinge pin to the shock mount position is the deciding factor on how much shock travel you loose per inch/mm of wheel travel. It doesn't matter if your suspension arm is 1" or 10" per mounting point on the chassis - The hinge pin vs shock mount position decides your wheel travel vs shock travel... Not the distance from the inner hinge pin to the shock mounting position. Sorry for the lamens terms but I try not to talk proper suspension dynamics lingo - most people don't understand it!!

#2 - You also have to remember - Our tire dynamics do not function at all like full size tires. Because of the ultra low profile and very stiff sidewalls (even on TC rubber tires) camber and camber change is, in my opinion, much more important to the traction and balance of my car than any Roll Center adjustment.

#3 - You guys are also forgeting about the amount of wheel scrub that short a-arms create vs. long a-arms. People think that short arms react faster and give them more rotation and steering - it is true - but why? Along with several other reasons one that is huge is that fact of wheel scrub - when the suspension travels up and down shorter arms essentially narrow the outside track width of the car as it rolls into the corner much more than long a-arms - this extra scrub generates more traction and quite possibly acts like a sort of chassis dynamic drag brake allowing people to "find" the entry and apex of a corner easier.

I've found this thread very interesting to see people's thoughts, opinions and who has tons of reading under their belt about suspension dynamics!! Keep it up everyone!! Oh, and as far as my opinions...I may be wrong....
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Old 04-07-2004, 09:07 AM   #43
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[QUOTE]Originally posted by elvo
[B]Alana - no, the other way around.

ok, thanks. i'll give it a try this weekend.
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Old 04-07-2004, 09:14 AM   #44
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josh,

i was actually just thinking last night that your comments would be very appreciated. you are opinions and observations are commonly considered the most respected of anyone's.

1) the inner pin location does indeed play a role in determining the ratio of wheel travel or rate vs. that of the spring. if you could imagine the arm's length going to infinity, it is simple to see, in this case, that the outer hinge pin and the shock pivot hole will essentially be moving the same vertical distance. this is, of course, not the case for the lengths permitted on our cars, so our ratio is in the neighborhood of 3:2.

2) good point. this could be the primary reason why a great deal of full scale tuning practices do not exhibit the same results in the world of 1/10 scale. i would love to see the traction curve vs. loading for the jacos that we run indoors. this could be revolutionary data.

3)the wheel scrub issue had been neglected thus far. i know little about the effects of wheel scrub. the literature that i have found about it indicates the desire to minimize the change in track width during bump/droop. of course that was one excerpt from years ago, and there really wasn’t a defined objective. note also that track width will only be decreasing if your arm pivots are lower at the chassis than the wheel. mostly, this is case, as the opposite alignment produces a very high roll center.

how would you describe the cornering characteristics of a short armed xray vs. the standard during entry, mid, and exit stages?

i would think i speak for many when i say we are very happy to get some input from someone that scrutinizes on track performance the way you do. and it certainly appears to be working. even with the c4.1 battery layout!

this thread was not meant to be a substitute for track time, but more to prove/disprove the allegations made for the short arms.

word.
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Old 04-07-2004, 03:36 PM   #45
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"long arms are also less sensitive to vertical roll center changes. whether the change is dynamic (on the track) or caused by changing tire diameter (common to foam tire racing) long arms minimize the vertical translation of the roll center."

Wouldn't a more sensitive car be better than a numb one? "I could really feel the changes with this car...."

"nfact, if in both cases the vehicle were tuned to exhibit the same amount of peak chassis roll, that vehicle which is described by the curve with decreasing slope (aka - short arms) would be stiffer for the early section, until near peak. huh. that's a plausible reason for why short arms cause the car to feel more reactive. initial stiffness!

but wait, isn't that also a characteristic of high roll centers? regardless of arm length? "


That intial stiffness is good to get without the problem of the high front roll center making your car want to flip on black grooved type tracks (aka nationals), or getting that "on the bumpstops" feel that can come from too high a roll center.

"in other words, on the xray, long arms = more angled links, while short arms = flatter links?""

In foam tire racing isn't reduced camber change considered to be a positive aspect ?? So we would want a flatter link...

"I have been trying a new car recently (atlas ym34si with "long arms") and have found that the biggest advantge is the speed it changes direction. I can make moves on the inside of ppl during s-turns that give me a huge advantage."

I have had atlas cars too and they did seem to have awesome sped in chicanes. It almost seems like maybe the long arms have a swaybar - like effect, keeping the car from ransferring too much weight. That kinda seems at odds with some of the other things posted here, but i am also a dummy./...
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