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Author Topic:   Rear weight affect
Racer0
Dirt Full Roller

Total posts: 64
posted May 08, 2002 11:49 PM
I need to get more rear percentage from my car. At the moment I have most of the weight just in front of the rear axle. Now if I move the weight back I should get more percentage with out adding weight, correct? So would it be better to move it back, or would there be to much of a "pendulum" effect making the car too loose. Or does the pendulum effect even exist? I am racing a metric car on a quarter mile track, medium to high banked. Any thoughts would be useful.

BGA
Dirt Roller

Total posts: 16
posted May 09, 2002 07:00 AM
My personal belief is that the pendulum effect is way over rated. Especially if you race on a short track. Now if you were racing on a big track I would agree with the pendulum effect.
I have about 100# just inside my rear bumper, and no I did not feel any more swing, but I did get more forward bite.
So I say do what makes YOUR car handle and makes YOU feel comfortable.
Bruce

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Deek
Dirt Full Roller

Total posts: 45
posted May 09, 2002 08:38 AM
I'm with BGA, with a street stock car on a short track, the gains from adding rear ballast to get the right rear percentages way override any pendulum effect. Give it a try and see for yourself.

racer17j
Dirt Forum Champ
Total posts: 1565
posted May 09, 2002 10:59 AM UIN: 54865418
my chassis man says to always add weight past the axle. anything in betwwen the wheels does not effect as much as whats behind them.says you can add 100# in front of the axle is the same as add 10# in the bumper.any truck drivers will notice this on the rear tandem when they slide them if you move the tandoms ahead 6 inches it will add about 200# to the weight thats on that axle same theroy here basicly

RangeRover
Dirt Maniac

Total posts: 174
posted May 09, 2002 12:40 PM
I'm glad to see that people are finally losing their fear of the "pendelum theory". Without a doubt, if you mount 300lbs on an extension six feet past the rear bumper, you'll feel it, but every saturday night on some dirt track in the United States there is a car with the right percentage and weight behind the axle that's spanking a guy who fears the pendelum effect. Guaranteed.

340duster
Dirt Full Roller

Total posts: 70
posted May 09, 2002 01:53 PM
OK you guys all this talk of ballast, rear weight percent, pendulum effect etc, I am going to try moving my ballast to the rear bumper area. (oh yeah I do fear the pendulum effect...maybe I read too many set-up books) I am going to do my set-up on Monday, what should I shoot for? Right now I have 120lbs ballast above diff on Right Rear and weight percentages (w/driver) 48% rear, 51% right and 50.5% Cross and it handles reasonably well - sligthtly loose
I will start and take the ballast and move it to the left rear bumper area and scale the car.
I will be shooting for 52% right, 52-3%, rear. Once I get that done how much wedge???
The track is 1/3 mile medium to high bank one groove bullring and is always dry or dry slick by the feature.
The race is May 18-19 and I will report the results and if I notice the pendulum effect. Hopefully I'll be doing the spankin' around here.............

Deek
Dirt Full Roller

Total posts: 45
posted May 09, 2002 02:25 PM
I just ran my new Duster (the third I've built over 8 years) and it handles quite well. There's a lot of variables that'll no doubt make your situation different than mine, but with that said, I'll give you my percentages. Rear weight 53%, left side 51%, cross 51%. I've only raced the new car once so far, but it's there. Maybe a touch loose going in on a dry track. 1.40" torsions, Landrum 200 lb springs in the rear (both). Using Bistein street stock shocks up front and AFCO's in the rear (a split valve on the left rear).
I have my weight mounted in the trunk area, mostly left side. Well over 200 lbs, but I can't remember the exact amount (I'm away from the car right now). sometimes I hang about 40 lbs (on the old car; haven't done it with the new one yet) high on the cage behind the driver on the left rear for dry-slick conditions (helps plant the RR on entry).
You're gonna have to tune your cross weight to your driving. I have always noticed on every Duster I've ran that as I add rear weight the car tightens on entry. You may need to take cross out for this, but with the torsion adjustments and stagger it shouldn't be a problem.
These are my experiences with the type of car you're running. I don't want to start an argument with the guys who insist a car loosens as you add rear weight or the Oh-My-Gawd-Pendulum-Theory-Advocates or the Add-Wedge-To-Loosen-The-Car-on-Entry-Proponents. Those folks can keep believing what they want.

Range Rover, by the way, said it best.

Deek
Dirt Full Roller

Total posts: 45
posted May 09, 2002 02:26 PM
Sorry, the torsion bars are 1.040" not 1.4".

340duster
Dirt Full Roller

Total posts: 70
posted May 09, 2002 05:39 PM
I just worked the numbers, I need About 220 lbs ballast at the LR to get to 52%. I had tight problems at turn entry and tuned it with wedge which made my exit loose....Hopefully with the extra forward bite it will help. Thanks for the ideas.

WesternAuto17
Dirt Freak

Total posts: 248
posted May 10, 2002 09:14 AM
All cars are different, as are all drivers. All else being equal, I removed the weight off the rear of trunk and it tightened the car up. The effect you guys say doesn't exist, I experienced in this car. That's not to say not to add a pound behind the axle, but just keep it in mind that the leverage creating more weight will also pull the rear out through a fast corner.

It may be over rated, but the pendulum effect does exist.

340duster
Dirt Full Roller

Total posts: 70
posted May 10, 2002 01:09 PM
Looking at the numbers for my car to get to 52% rear I would have to add 370 lbs at the rear axle or 200 at the rear bumper. So the real question is the 170lbs difference. What makes the car slower more pendulum effect or 170 extra lbs and no pendulum. I am going to try the weight at the bumper for the May 18-19 race weekend and see

BGA
Dirt Roller

Total posts: 16
posted May 10, 2002 01:41 PM
Please let us know how you feel about the ballast issue after you try it out. Good luck on your upcoming race.
Bruce

racer17j
Dirt Forum Champ
Total posts: 1565
posted May 10, 2002 01:54 PM UIN: 54865418
here is the way i see it i have felt the pendulam affect before but not in my race car in my street car on the track messing around with a 1/2 tank of fuel one nite when they left the gates open.i could feal the tail shake as the fuel goes froms side to side but the fuel is not bolted down like the lead is

340duster
Dirt Full Roller

Total posts: 70
posted May 22, 2002 12:00 AM
Race results from ballast addition are in:

Saturday
Time Trial: Fast Qualifier
Trophy dash: Win
Heat1: 2nd
Heat2: 2nd
Feature: trans line broke - DNF
Sunday
Trophy dash: 2nd
Heat1: 2nd
Heat2: 2nd
Feature: 2nd
So the weight will stay at the bumper!!!, this is my best weekend to date... I am still a little loose on the dry slick so I plan to remove a leaf from each rear spring to gain a little bite....any thoughts?


RangeRover
Dirt Maniac

Total posts: 174
posted May 22, 2002 07:49 AM
THAT'S what's up!

WesternAuto17
Dirt Freak

Total posts: 248
posted May 22, 2002 08:53 AM
Pendulum, shmendulum. If the car is faster, it doesn't matter.

ryan
Dirt Freak

Total posts: 430
posted May 22, 2002 01:39 PM
I have never really noticed a pendelum effect but put the weight were it feels best to you. Every track and driver is different. In other words do "whatever trips your trigger"

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