Conference oass::racers

There are a bunch of things which the proper corner weights depend on. 

You use corner weights to help balance the car for the type of driving 
you are going to do as well as for the type of car. The weights have 
to be biased both front to rear and left to right.

In general you add weight to the corners which you want to get more 
traction (to a point). If your car understeers you would want more
weight on the front. If the car oversteers or can't get the power down
you want more weight on the rear. 

If you predominantly turn in one direction you would want to put more 
weight on the inside wheels. Oval track drivers put more weight on the 
left side. When they go through a left turn weight shifts to the 
outside giving the outside tires more grip but reducing the grip on 
the inside. By starting with more weight on the inside this transfer 
will tend to even out the weight and allow you to use all four tires 
more efficiently.

For street driving you generally want to balance the car evenly from
left to right. For a track like Lime Rock which only has one left turn
and it isn't too important I put a few percent more weight on the
right side of the car. 

The first thing to do before changing anything is to write down what 
your weights currently are.

If you generally do street driving with the car and you like the 
balance of the car as it is, keep the front to rear percentage the
same and balance the car evenly left to right. 

ie:     Current                    Proposed

    L.F.: 400    R.F.: 500       L.F.: 450    R.F.: 450
    Total Front: 900             Total Front: 900

    L.R.: 600    R.R.: 500       L.R.: 550    R.R.: 550
    Total Rear:  1100            Total Rear:  1100

It's easiest to get the weights on opposite corners. If you raise the 
right front you will be increasing weight on the right rear AND left 
front. It can be a real juggling act to get them the way you want.

It helps if you can find someone who weighs about the same as you and 
won't complain for a couple of hours sit in the car (and not move).

IMPORTANT:::  DISCONNECT THE SWAYBARS -
After you have the weights the way you want, adjust the swaybar drop 
links so there is no preload on the bar when you re-connect it.

Drive the car and decide how it feels. Re-balance as necessary.

For my underpowered 914 (mid-engined) I think I started with about 58%
rear and 42% front.

    	In general, for roadracing you want corner weights to be balanced,
    left-to-right. Doing otherwise will make the car turn well in one
    direction but be a pig in the other. The only time you really want to
    get weights dissimilar is when all the important corners (those leading
    onto or off of a straight) are in the same direction, like at Lime Rock
    here in the USA, or for an oval. Even then you have to keep the car
    controlable for the non-critical corners in the other direction.
	- Chris

160-170 Bhp  at the flywheel 130+ at the wheels.
	U.K. Club circuits including Brands hatch, Silverstone, Thruxton,
Snetterton, Cadwell, Oulton, Mallory. "Street" circuits not "Ovals"

	Lotus 23 replica weight about 600Kg

I know Brands and Silverstone have a good mix of left and right turns so
I would think you want the car to be pretty evenly balanced left to right.

Again, do you like the way the car handles right now? If so keep the front
to rear balance about the same and set the left right weights even. If
I were setting the car up from scratch I would go between 55% to 60% in the
rear to begin with. If you haven't done corner weights before you may be
happy to get within that range with left and right close to the same
weight.

My guess is that if you ran more at Silverstone you would want a little
lower weight in the rear (fast turns probably no problem getting the power
down), and the short course at Brands a bit more weight to the rear to get
the power down in the tighter turns.

Let us know how it goes.

What type of scales do you have?

    
    one more (of many) things to keep track of:  tire pressures.  try to
    duplicate the tire pressures that are seen in competition.  when you
    think about it, the tire pressure is supporting the weight of the car,
    not the rubber compound of the tire.
    
    and another;  if the floor surface is not level, your corner weights
    will not be accurate.
    
    adding to glenn's comment on the swaybar being disconnected during this
    procedure, convince that nice person who's weight closely matches
    your's to stay in the car while you RECONNECT to swaybar downlinks.  (I
    use dumbbell weights because that don't talk back, complain about the
    garage being a second home, etc. etc. etc.)
    
    and there's more:  if you have concerns about cutting minimum car
    weight at the end of your race, put the car on the scales, note the
    total weight, and THEN refill the tank, noting the difference.  also
    note if the weight seems to end up on one corner, or evenly
    distributed.
    
    and of course you have adjustable shocks, which for one track you like
    soft, another you like stiff, and, you guessed it, they also effect
    corner weights!!
    
    isn't this FUN!!!!!  how much time before that next race?????
    
    
    and we haven't even touched on suspension geometry yet!!!!
    
    
    Bob Roth  

A little over 2 weeks before Brands Hatch.....

    and as I recall when we did the suspension adjustments on the Royale
    (several years ago), the ride heights and corner weights interact, so
    you also should check the car's stance as part of the process.
    
    Good point in .-? about rechecking with empty and full tanks, not just
    for gross vehicle weight but also for distribution - most good designs
    should NOT change the weight distribution as fuel load burns off, but
    it's certainly an easy thing to check and could be worthwhile.
    
    Bob's comment about using weights (dumbbells or sandbags are favorites)
    to substitute gives a good approximation, you might get a small change
    when you substitute a live driver because you have legs and such that
    make the distribution somewhat different, but that's probably not
    significant on a gross level anyway.
    
    Most important, use a level floor.  Also, what mechanism do you have
    for measuring each corner?  The one we used, which I liked, is four
    electronic scale pads connected to one central box that displays all
    the corner weights at once.  Using anything less precise (eg, bathroom
    scales) would probably require some checking for linearity and
    reproducibility between all four units before you measure the corners.
    

 I talked to the cars original owner/builder and they've never been done!

	old corner weights	    new corner weights

Front	107	135			118	129
	

rear	192	179			185	188			
	----------------		-------------
	299	  304			303	 317	Target	

	

            <<< MARVIN::DISK$TOOLS:[NOTES$LIBRARY]CARS_UK.NOTE;1 >>>
                            -< CARS_UK conference >-
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Note 576.414                Driving & Racing kitcars                  414 of 418
VANTEN::MITCHELLD "Network Consultant"               67 lines  28-OCT-1991 18:16
                               -< A bit further >-
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A car has wheels  front wheels a left front, b right front, c left rear, d
right rear.  

		A    B


		C    D

are the four wheels weights.

using  moments for any car  	A+B 	= K1
			 	C+D  	= K2
				A+C		= K3
			 	B+D		= K4
			 
where K1, K2, K3, and K4 are constants related to the position of
the C.G. and the total weight and dimensions of the car.
( Note K1+K2 = K3+k4 = total weight of car)

e.g. K1 = (Total weight X C.G distance from rear)/ wheel base

But to prevent diagonal distribution of weight the front  wheels
should be loaded in proportion to the total left/right distribution

i.e.	A/B= K3/K4

and so the back wheels C/D=  K3/K4

A + B = K1 so B= K1-A then

	A/(K1-A) = K3/K4

	A = ((k1-A)K3)/K4 = K3K1/K4 - K3A/K4

	A(1+K3/K4)= K3K1/K4

	A= (K3K1/K4)/(1+K3/K4) = k3K1/(K4+K3)

	
Worked Example:   a car was weighed as shown below


		40 	60    

		

		80	30

	A=40,b=60,c=80,d=30,k1=100,k2=110,k3=130,k4=90

using the above formula and and similar

The balanced corner weights are

	A'= k3k1/W = 100*130/210 		= 61.9
	B'= K1K4/W = 100*90/210 		= 42.9
	C'= K2K3/W = 110*130/210		= 68.1
	D'= K2K4/W = 110*90/210  		= 47.1 

Where W is the total weight i.e W = K1+K2 =K3 +K4

Target corner weights are

		61.9	42.9


		68.1	47.1

Which can achieved by lowering the bottom spring platforms on b and c
From this basic point you can then set it up for a circuit or leave it with
the basic set up for a road car.