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Author Topic:   weight placement/sidebite question
justin
Dirt Maniac

Total posts: 167
posted January 07, 2003 06:57 PM
When would mounting weight up high in the chassis (ex. head high) benefit the car the most? Wet/tacky track or dry/slick track? I've seen people do this for both track conditions. I think it would be better for when the track goes dry/slick to help give the car more sidebite, but like I said, I've seen it both ways. So under what track condition will this benefit the most. Thanks in advance.

Justin

justin
Dirt Maniac

Total posts: 167
posted January 12, 2003 08:49 PM
nobody wanna take a stab at this?

malibuchevy2
Dirt Full Roller

Total posts: 43
posted January 12, 2003 09:15 PM
the only reason people do it is to get the car to body roll more i think

justin
Dirt Maniac

Total posts: 167
posted January 12, 2003 09:40 PM
Yeah I know they want more body roll but do they want it for a tacky or slick track? I would think it would be for a dry/slick track.

ryan
Dirt Freak

Total posts: 430
posted January 14, 2003 08:02 PM
I would say for a dry slick track. The way I look at it is if its up high is pushing the tire down more and when its lower it would push on the sidewall more. Dont know if it makes sence on the screen but it does in my head

JDF Motorsports
Dirt Roller

Total posts: 19
posted January 14, 2003 10:03 PM
Okay man, I've played with this a bunch and here is my opinion. Yes, the higher the weight, the more roll you car will have...but it is the wrong kind of roll.... Yes it plants the RR but unloads the LR. That is NOT what you want on dry slick. This will cause you to be tight in and loose off. Loose off because you have loaded the RR so much more than the LR, therefor under throttle the RR bites harder than the LR and you will have a loose car. Now you may say "Look how much a latemodel will roll." This is true but they roll by planting the LR to the ground using control arm leverage, not by planting the RR even though the body roll may make it appear so. Make sense? Here is what I worked on all last year and it seem to just get better and better. Load the LEFT REAR, plant it to the ground using a combination of weight and wedge. Now acheive your body roll by using softer springs. Also play with rear spring split. To me this made the car looser in but it would tighten the instant you put the gas to it. You CAN take this to an extreme and cause too much push. You just have to play with it to find what works for your driving style. If you want sidebite, go soft on the springs to get your roll, not high on the weight. This will allow you to find sidebite and forward bite too. Hope this helps. Its just my opinion....not the gospel.

c21
Dirt Freak

Total posts: 346
posted January 15, 2003 10:41 AM
I would have to agree with JDF Motorsports.

and ...
Placing weight higher raises the CG height relative to the roll axis (and pitch axis) ... creating more weight transfer. This is bad for cornering (in my opinion) but can be helpful for straight-line acceleration (because it also transfers more weight rearward when you get back on the throttle).

you can play around with this, but I think LR loading is critical and is not served by this practice.

c21

justin
Dirt Maniac

Total posts: 167
posted January 15, 2003 07:26 PM
Thanks for the input on that fellas, it makes a lot more sense now.

Justin

ryan
Dirt Freak

Total posts: 430
posted January 15, 2003 08:16 PM
jdf- how light of springs would you think are you talking really light spring rate or just #50 or so less than normal. At my track a guy I get along with pretty well was in the top 2 and he had 1000,1200,250,225. I want to be in that range but I was thinking maybe 900,1100,225,200. His setup was good but I want to be better than him! This is a fast 3/10th 3500lbs metric.

JDF Motorsports
Dirt Roller

Total posts: 19
posted January 15, 2003 10:03 PM
Ryan, depending on the track I think your set up would be the one I prefer. Up front I ran 1000 LF, 1150 RF, 200&225 LR, and 175&200 RR. 3350lb metric. I was definiatly in the ball park with that set up. I was running against cars that were lighter, more hp, and better chassis %'s.(consistant top 3's at the end of the year) This year I bought some different springs to play with. Gonna try going really soft up front but continue to work on planting the LR even more. Who knows what will happen....we shall see. The biggest think is don't be affraid to try different things. Take different setups to play day. Do the work, and be willing to learn from mistakes. It will help.

66jj
Dirt Freak

Total posts: 352
posted January 16, 2003 05:19 PM
jdf

what do you call super light in front?? i ran the heaviest i owned on a dirt track 800 straight accross against guys who said they had 12-1300, it was a 5000 to win open comp, i got no practice, never saw the track before time ins and was racing a pavement street stock..

i qualified 3rd fast, and was leading when i got took out by a local, full invert start 30 cars, so id say lighter than you think can work, that track by lap 60 of 75 had one foot ruts at one end no kidding..

it was a 3300 lb camaro.

like you said try everything, youd be surprised. i found on pavement the lighter my car the heavier spring i had to run, at 2850, 600-650 traveled 4 inches in front,the valances were rubbing on entry and exit, while 750-800 was more normal, 1-2 inches.

but at 3300 i could run the 600-650 just fine....

the light springs in front changed how much the rear squated also, way more with the lighter car and light sp.

lighter was just that much free'er. i wouldt have ever thought...

im gonna be racing dirt soon, and will be trying 600-850 up front, so well see, i have all those!!!

JDF Motorsports
Dirt Roller

Total posts: 19
posted January 16, 2003 05:48 PM
66jj, gonna try a 850-950 set up to see what it does. I'm not brave enough to jump down as low as you....yet....LOL
Good luck

c21
Dirt Freak

Total posts: 346
posted January 17, 2003 10:39 AM
How much a car lays over is largely determined by:

lateral acceleration (much higher on aspahalt).

car weight (more weight, with all else equal will compress a spring more .... as it is transferred)

and

Center of gravity height


the tendancy to roll over is resisted by ....

roll resistance which is largely determined by tire stiffness (pressure/sidewall type), wheel spring rate, sway bars, and roll axis height (and for a short amount of time shock valving).


So .....
an increase in lateral acceleration, WEIGHT or CG height will increase body roll if roll resistance remains the same .... (sorry, thems the laws).


I think you (66) found the right set up, but may have drawn the wrong conclusion ... I'm guessing your lighter car needed more spring because of an increase in lateral acceleration (or you made some suspension geometry change that "freed it up " as you said).....not because of a decrease in weight.


On a related note .... I like soft springs up front on dirt. They work well with a high left percentage. I have found that by running my fronts reversed and soft (900 LF and 750 RF) I can run more static cross which helps my exit out considerably.

P.S. nice job on sorting out that foriegn track quickly and getting a 3rd fast (no better way to tick off the locals).

c21

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