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Old 04-07-2004, 03:46 PM   #46
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"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 am not sure if the rubber tire guys like short arms as much but this would explain why all these cars started with long arms. Wheel scrub = bad according to most tuning theories (full size). Obivously, foam tires is like racing on Mars compared to full size. Encouraging scrub could also be good in terms of trying to get the tire to twist or deform-- it may produce better handling due to a spring like effect?? Or how about the idea that the car likes to get "up on the tire", that scrub will set the "spring" of tire so that it reacts faster.
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Old 04-07-2004, 05:23 PM   #47
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seaball - To my comment on #1 - measure a long arm Xray TC and then a short arm Xray TC. If you use the same hub carrier, wheel spacing and same shock position distance from the king pin your wheel travel vs. shock travel is nearly identical (I know it's not exactly the same). You will loose a very very minimal amount of shock travel vs wheel travel but what you loose in shock travel you gain back (by a much greater margin) shock angle. This more vertical (and more progressive) action of the shocks also makes the cars transfer faster - I also think it may actually create more shock travel than a longer a-arm.... To simulate this type of action on a longer a-arm car you would need a much shorter shock... agree??

#3 - We adjust "scrub set" on our 1/8 Kyosho cars all the time. In the front it does act a little different as with the pillow ball system it does effect steering jacking. In the rear we can adjust it and I do on many occasions depending on the traction and layout of the track. It is hard to say because when you adjust this it changes a-arm length, wheel to hinge pin offset, camber change, etc.....

My long a-arm Xray was extremely stable but the large thing I noticed was the fact that the car wouldn't decelerate with steering input the way that other cars that I have ran would. I was able to get the car to initiate into a corner the same as my short a-arm car but it would always give up the front end in the middle of the corner and usually exit the corner smooth but with understeer. Lap times were consistant but not up to the pace needed (especially for mod). I must say though - through highspeed chicanes it was so comfortable to push as hard as I wanted. I also really want to go back now and test everything again - with what I have learned this year with the Xray I definatly would love to give the long a-arms another shot!!

What do you mean even with the c4.1 layout?? What's wrong with it??
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Old 04-07-2004, 06:20 PM   #48
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Dragonfire

As for being faster around the track???? Well its up to the driver to exract the performance for that.. 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.


So whats better??? Alot of crap is said about this car has this and that car has that. A car is fast because of the driver and that fact will never change. As long as the car is adjustable (modern) you will always have the potential to be competative.
Dragonfire, My opinion Too, its up to the driver !

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Josh i must say, you truly exhibit an excellent driving talent in Nitro or Electric
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Old 04-07-2004, 07:57 PM   #49
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Hey Seaball, here we go again!

I feel a little under quaified to post here but what the heck.

I think any change in performance has more to do with the camber gain and lateral roll center movement than anything else. If the roll center moves toward the inside of the turn the roll resistance should stiffen. This would help keep the car flatter through the turn. But as Josh said the car will not want to go through the tight switch backs as well.

As far as camber gain is concerned, while you can change the upper link to get a long arm to provide similar total camber gain, the short arm would tend to gain more camber per inch/mm of suspension compression particularly in the early stages of compression. So, if you have stiffened the roll resistance you would require more agressive camber gain per inch/mm simply because the chassis will not roll as far as it would with the long arm set-up.

The idea of shock travel has some merit. If I'm not mistaken a short arm should increase the velocity of the piston which would also stiffen the roll resisitance. This may act similar to having a sway-bar on the car, or maybe a stiffer one at least. If nothing else, the car will tend to corner flatter because the extra velocity creates more "pack", which in turn limits shock movement.

I'm no expert on this subject but I have some gained some real world knowledge about roll centers and camber gain through working with full size circle track cars.


This has been another thought provoking thread brought to us by Mr. Seaball, nice job, see ya at the track!!! Chris
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Old 04-07-2004, 08:06 PM   #50
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Quote:
Originally posted by Josh Cyrul

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....
Josh....Seaball really does not understand a thing he says. He just throws out a bunch of big words and sometimes they sound good. Hell, he can barely dress himself
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Old 04-07-2004, 08:29 PM   #51
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i'm gonna throw my .002 pesos in too. i just "re-aquired" two X-RAY T1's i used to run on carpet. they are bone stock...pillow-ball and all! i must say that i can agree with josh on the way the car behaved. the thing would go in good and deep, but mid to 85% corner exit the thing would wash out!! so i'm gonna let the cat out of the bag. i have a couple of sets of "short" pillow ball a-arms from a few cars. including the Ntc3 old and new front and rear arms....i plan to try having a short pillowball arm x-ray and a long pillowball arm x-ray. i know these efforts may be in vain but, since i had the part here...i might as well see things for myself. and who knows....i might be able to find a little gold nugget somewhere in there.
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Old 04-07-2004, 09:05 PM   #52
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Chris and seaball-if I ever fulfill my dream of racing a Formula Continental or Atlantic-you guys are both SO HIRED for the team. Now-which one of you brainiacs would be the Engineer and which one would head up the test team!!

You guys blow me away!!

Ray
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Old 04-08-2004, 03:54 AM   #53
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Originally posted by Cole Trickle
Hi Peter

Here there's an explanation about length of camber lengths and angels. Go to "suspension" and eventually the section "Touring setup guide".
that's my site ;-)

That link is the old one though, I can't update it any more.

The new link is http://users.pandora.be/elvo
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Old 04-08-2004, 04:18 AM   #54
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#1: no, not really. You have to look at the arm as a lever on the shock. if you lengthen the arm and leave all other stuff the same, you lose leverage and stiffen the suspension. just draw a simple diagram and you'll see it.
Also: the amount of offset in the hub has to be taken into consideration. Difficult to explain.

#2: I think roll center is pretty important. more than camber change. But then, I'm a buggy man :-p

#3: exactly. that could be the key here, to find the answer to the original question of the thread. The only thing that you can only change by changing arm length is (rear) wheel scrub. And even if the wheels scrub... less than a millimetre, it's still pretty important. In a way, the thing you do to your evolva front end is the same thing, only it's based on the steering, not on chassis roll. (you use different hub carriers, right? or you use the same carriers, but space out the axle?)

The Losi XXX BK2 has variable length arms, which is super nice. i've only begun to play around with it, but the things i'm feeling so far are exactly the same as on the XRay TC.
long arms are very nice for long sweepers, you can push the car more. it even feels as if the car has more traction. And it's jsut way more stable overall. You can do anything, and the car will always sort itself out.
Short arms transition much faster, both in and out of corners, which can mean you gain a few tenths per lap, on tight, twisty tracks.

BTW - I want a C12! ;-)

Quote:
Originally posted by Josh Cyrul
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 04-08-2004, 04:31 AM   #55
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#2: Our rims flex. Full-scale cars use alu/magnesium rims, they don't flex.

Quote:
Originally posted by Josh Cyrul
#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.
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Old 04-08-2004, 08:03 AM   #56
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hey josh, perhaps the xray arms don't yield much change in leverage if some of the other geometry is differnent as well. i was just speaking in regards to the general case of changing arm length leaving the other geomety unchanged.

for anyone interested in this subject, or suspension kinematics in genaral, i would highly recommend dowloading that program mentioned below. the download is free and it gives a picture of what is happening to the concrete, as well as, the abstract (roll center ) thank you jeff c for that. i have wanted something like that for a while now.

ccm399 - i have stayed away from the topic of lateral roll center movement because i am unclear about how this affects roll. specifically refering to the coupled moment between the cg and the rc that is accountable for any chassis roll. because the component of force acting through the cg is always horizontal, i cannot see why a lateral change in rc affects the magnitude of chassis roll. i will assume that i am not recognizing another aspect here. what is it?

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Old 04-08-2004, 12:44 PM   #57
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Sligthly off topic: Thanks for inspiration to re-experiment with camber links and camber gain. I now used angled camber links, which suits me nice on a tight track. My car is very responsive now - almost too responsive - considering thicker shock oil !
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Old 04-08-2004, 01:59 PM   #58
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Quote:
Originally posted by seaball
i have stayed away from the topic of lateral roll center movement because i am unclear about how this affects roll. specifically refering to the coupled moment between the cg and the rc that is accountable for any chassis roll. because the component of force acting through the cg is always horizontal, i cannot see why a lateral change in rc affects the magnitude of chassis roll. i will assume that i am not recognizing another aspect here. what is it?
I'm still a little uncertain on the effects of lateral roll center movement myself. A few of us have talked about it in reguards to our 1:1 stock cars, but nobody "let out" any really good information.

My own feelings/opinion is that moving the roll center to the left/right of the car, could act as a lever to make the whole car compress or rebound throughout a corner. If the RC stayed exactly at the centerline of the car, one would assume that half the car would compress, while the other half would rebound an equal amount, right? In a left hand corner, the right side goes down, the left comes up. But if the RC was to the inside of the car in that same left hand corner, would that make the right side of the chassis compress more, and the left side rebound less??? I don't know. How about this, again in that same left hand corner, if the roll center was exactly at the center of the LF tire contact patch, would the left front of the car travel up and down at all??? Again, I don't know. I could be completely 100% off on this, and hopefully somebody with a better understanding can shed a little more light on the subject of lateral roll center location.
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Old 04-08-2004, 04:40 PM   #59
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thanks jeff. you hit the nail on the head. and really, so did ccm399, but i didn't yet visualize.

indeed i have left out a huge, very huge and obvious part, of the equation. the restoring couple generated by the shock. that couple is related to the distance that the roll center is from the shock pivot. and, i might add, it is directly affected by both horizontal and lateral roll center movements. in our cases, more by the lateral movement!

man, jeff, that was perfect. given a roll center that would remain centered horizontally during all stages of cornering, the amount of inside body roll up, should equate to that distance down of the laden side. but by allowing the roll center to shift, the ratio of up travel (of the inside) to down (of the out) is shifted as well.

wow. again, nothing short of significant in my opinion.

so now we have established that the shorter arms are causing more movement of the roll center in both horizontal and vertical directions. while moving the rc down causes more roll compliance with increasing roll magnitude, the lateral movement is causing the opposite. is the resulting stiffness vs. roll curve back in line with that of the longer arms?

i guess we need to explore the magnitude or ratio produced between the two movements. I still think the vertical to be overpowering, but i have not really done the math. i am imagining approximate lengths, and the cg to rc is a much shorter distance. at least for our 1/10 chassis.

we could probably bust out that nifty program and get some answers shortly.
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Old 04-08-2004, 04:47 PM   #60
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Talking

this discussion is heading more and more toward a ridiculous differential equation. oh god no.

the crazy part is that all of this is, and has been, done by many people in full scale racing. this information should be plentiful. or is this all under wraps for all of the various teams out there?

nah, we aren't even discussing anything close to what these guys would consider secretive

and what am i doing in sales??

i guess, just being jealous.
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