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Old 01-23-2004, 07:56 PM   #1
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Default Corner weights and chassis balancing

Hey guys, I know there are a few of you out there who take advantage of the use of small kitchen scales to corner balance and weigh your race car. Exactly how are you achieving a balanced setting without upsetting the ride height of the car using scales?

I know when we corner weight our real race car, it is done with push-rod-type levers, which directly or inversely effect only the weight of each corner, and ride height is done with different adjustments. This setting and adjustment time is absolutely critical to setting up the car to be competitive. On a coil-over independent suspension car, how do you achieve at least a balance from left to right tires?

Also, what f/r weight distribution is common among 10th scale 4wd touring cars? I'd love to hear how some of the pros use weight distribution to their benefit.


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Old 01-23-2004, 07:59 PM   #2
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Its pritty much the same thing as checking for tweak. So I'd get a tweak board. Integy makes a good one.
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Old 01-23-2004, 08:07 PM   #3
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Tweak boards can't do front to rear weight distribution and are good for only getting a left to right balance on one axle at a time. They also can't help you dial in accurate weight jacking if needed on a particular track.

Now, back to the question about scales.


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Old 01-23-2004, 08:40 PM   #4
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this could be a great thread.

i'm not a pro, but i am very analytical. i too want to see what the average weight balance is for a successful sedan chassis in some specified conditions.

so far for me, it seems that carpet/foam cars can benefit from some extra weight up front. the severe amount of grip still allows the front to be responsive despite it's added mass. it seems like it even calms down the front of the car. our fast guys seems to be almost dead 50/50 f/r with the american sedans.

i think asphalt is a different story. and i emphasize think. just like one ways prevail outdoors, i think a small weight differential might be appropriate as well, to give good turn in characteristics. i have very little experience outdoors, so my comments are merely based on physics, and observations of the team driver setups. it is very common to see balancing weight applied somewhere to rear half of the car on those using rubber tires.

is my thinking flawed?

pros, we need you here.

as far as l/r balance goes, you can't really acheive this if your weight distribution on the chassis is not balanced. while it may look like you can on two scales, four scales would show you that you would merely be jacking either the front or rear axle, at the expense of the other on that side. at least statically, anyway.

what's amazing to me is the sensitivity of the four scale setup. while it's a pretty thing to see being used, i've ever met only one person who acutally calibrates their scale setup board. with the poor manufacturing tolerances of these cheap postal scales, i would be surprised if the individual heights were within .010 of each other, and are even dead flat across the top plate. that's a significant amount when the resolution of the scales is 1 or 2 grams. worse yet is that sedans won't even tell the tale if you are off a few grams anyway.

props for the thread.
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Old 01-31-2004, 12:17 PM   #5
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Bump... this seems to not have gathered enough speed the first time.
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Old 01-31-2004, 05:44 PM   #6
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One thing you have to remember is that L-R and F-R weight balance has to be done with physical weight no amount of tweak will change those percentages. Just like a real car works. First alwayse start with ride height set it then move weight or add weight to balance out those percentages and then set tweak. Tweak is called wedge in a full scale car. I tried diferent F-R percentages and went back to 50-50 balanced both ways. If you have your ride height set perfectly and your percentages set right tweak will be right also. If not something is wrong. This was almost impossible to get set right until I got screw adjustable shocks.
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Old 01-31-2004, 08:27 PM   #7
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I had always only ever used the Left - Right balancing method, but since getting access to one of those integy balance stations, it is quite interesting to see that even if balanced left to right, it can dramatically be out at each axle, with my current electronics layout on an xray i had to add 30 grams to the RR, and 20 grams to the LF. now it is much easier to maintain chassis tweak.
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Old 02-01-2004, 09:33 PM   #8
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Quote:
Originally posted by SpeediePHATT
One thing you have to remember is that L-R and F-R weight balance has to be done with physical weight no amount of tweak will change those percentages.
Well, actually, that's not true. You CAN adjust the amount of weight on the F/R and L/R by changing the preload on the 4 shocks. It's simple levering of a coil-over car. Oval cars do it all of the time. It does, however, effect ride heights of the 4-corners when done this way. You can also change the weight of each corner with different spring rates on each wheel. All you are doing is changing the force of gravity on each tire.

Ideally, I'd like to know if anyone using scales to corner weigh their car is using a weight bias to the front or rear, or is trying to balance the car to a 50/50 weight distribution.

To me, a tweak board will tell you if both left and right tires of a particular axle are being pushed down to the same position (level), but it can't tell you the force being applied to each tire in a static state.

I know lots of guys use individual scales for setups, but it seems like there is a "black art" to it, and no one wants to give away their secrets.
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Old 02-02-2004, 12:16 AM   #9
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Here was a previous post re:weight distribution system.
http://www.rctech.net/forum/showthre...threadid=27578

Not sure if it is relevent to your questions, but it might be worth a quick read.
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Old 02-02-2004, 12:59 AM   #10
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Quote:
Originally posted by ApexSpeed
Well, actually, that's not true. You CAN adjust the amount of weight on the F/R and L/R by changing the preload on the 4 shocks. It's simple levering of a coil-over car. Oval cars do it all of the time. It does, however, effect ride heights of the 4-corners when done this way. You can also change the weight of each corner with different spring rates on each wheel. All you are doing is changing the force of gravity on each tire.
Sorry but it is true just try it, or read any chassis set up books and you will see. Whenever you load one corner shock more or unload it you are doing the same exact adjustment to the opposite corner of the car. And that keeps all of the F-R and L-F percentages the same. Those have to be done with physical weight placement nothing else.

Also and I dont want to sound like a troublemaker, but the springrate has nothing to do with weight percentages. All that does is dictate body roll the percentages are still adjusted with the collars. Thier is no secret sience it is quite simple if you are willing to find the information. Our cars are scale models, but the physics and theories are almost exactly the same. Just read any full scale chassis set up books and you will learn all you'll ever want to know about scaling and chassis set up. Here is a site that sells books about all auto racing steve smith autosports. Feel free to disagree but I have been setting up oval cars very suscessfully for 15 years and Im sure Im right.
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Old 02-02-2004, 05:22 PM   #11
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Hey,

I must say I totally agree with SpeediePHATT. I've never liked the idea of a tweak board, to me it's just a kind of DIY. There's nothing better than weight added at the proper place. The best would be to calculate the matrix of inertia of the car and place them so that the matrix has only terms in the diagonal, but it's a bit of a hassle

All I can say is that on my SD, the weight distribution is equal L/R on both front and rear, but not likely 50/50 (couldn't achieve that with the battery such backwards). I've never suffered from "tweak", I never put my car on a tweak board, my colars have the same preload L/R and the car is even, even after a crash.

Though, I've been playing with the arms position. On the SD you can move both the front and rear wishbones 4mm. This not only changes the wheelbase, but also the mass balance. I've moved them all backwards and the car has much more steering, and does not overheat the tyres (which I've suffered from this summer).

I think for rubber the best is really 50/50, as the tyres will provide the same amount of grip, they will heat up and wear almost the same. For foams, as the width is not the same on front and rear, it should be a better idea to keep more weight on the rear.
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Old 02-02-2004, 07:22 PM   #12
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I stand corrected. In my head, I was thinking of adjusting weight transfer with F/R ride height adjustments, but you are correct, the numbers cannot be changed without physically moving weight around in the car.

Having said that, I am now to assume that you are placing weight and components in the car to get an even balance from left to right and front to back?
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Old 02-02-2004, 08:11 PM   #13
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I've seen something like this, It was on a RC Car action mag. It was like a 97 issue.
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Old 02-02-2004, 10:27 PM   #14
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To get the balance right I did the battery mod and moved them inboard. And placed my reciever on top of my servo, my GT7 right behind the servo and only add 14g next to the servo to totally balance at 50-50 both ways. The track i normally run on tho doesnt have alot of grip. Im thinking when I got to a track with alot of grip the front will want to be lighter than the back, ANd ill have to move the electronics back or the batteries. I also tape my batteries instead of using the strap.
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Old 02-03-2004, 03:40 AM   #15
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I did the servo mod on my SD, and my electronics layout is the same as speediePHATT. I still have a difference L/R that I balance with added weight on the extreme right of the servo (vertically on the servo case), weight that I would still need anyway as my car is 50g underweight.

I'm planning on making a new chassis, with the cells moved a bit forward and closer to the centre of the car, narrower and milled under the electronics and the servo to lower them.
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