At 02:04 PM 1/22/02 -0700, GSMnow@aol.com wrote:
[snipped]
>I recomend Fred Puhn's "How to Make Your Car Handle"
>ISBN# 0-912656-46-8
>I paid $10 for it a long time ago.
Definitely a good book. They are often available today on the Internet in
used, but very good, condition for $7-9.00US.
>So for the newer perspective, read Don Alexander's book,
>"Performance Handling" techniques for the 90's
>ISBN# 0-87938-418-2
Thanks for this tip, I'll look for it.
>The idea behind corner weighting is to make the tires all work the same while
>turning in either direction.
The trouble is that while turning, the outside wheels work much harder than
the inside, because of the weight transfer. All 4 tires will not work the
same, especially when the inside wheels get light and the outside wheels
are carrying most of the load. What you *can* try to do with corner
balancing is to get the F/R weight distribution the same on both sides of
the car, which will make the handling more predictable if your racing
involves turning both left and right. Roundy-round guys are in another
ballpark.
>For example, lets say you have a front drive car with the engine offset to
>the drivers side. You put it on a set of four scales and get
>
>LF 750 pounds RF 700 pounds
>
>LR 500 pounds RR 350 pounds
>
>This does not look very good, and it can use some adjustment.
[snipped]
It should probably be mentioned here that you want to take these weights
with the driver in the car (or the equivalent of their weight in the
driver's seat, anyway).
>By adjusting the spring preload on each corner, you could get something like
>this.
>
>LF 775 pounds RF 675 pounds
>
>LR 475 pounds RR 375 pounds
>
>This still looks very bad, but is not as bad as you might think.
[snipped]
>What we want to get equal are the diagonal totals.
>LF + RR = 1150
>RF + LR = 1150
This is not always true, as Puhn shows in his book. Although getting the
sum of the diagonals equal is a popular method which will get you close, it
doesn't render an ideal corner balance, unless your car has either 50/50
F/R or 50/50 L/R weight distribution, neither of which this hypothetical
car has. Of course, exact adjustments are not always possible or even
necessary, but you should be shooting for the ideal and get as close as you
practically can. Something like +/- 40 lbs. is probably plenty accurate
for this kind of work.
The ideal corner weights for this example would be:
LF 788 RF 662
LR 462 RR 388
Note that the diagonal totals for this are:
LF+RR =1176
RF+LR =1124
This setup has more than 50 lbs. difference between the diagonal sums, but
what you will find is that the F/R weight distribution is the same on the
left side of the car as it is on the right side this way (63%F and 37% R).
Look at Puhn's formula and this will be clear. Since it is the relative
weight distribution Front/Rear which determines the handling balance of the
car (understeer or oversteer), all else being equal in a given example
(tires/shocks/springs/alignment, etc.), when you load the left wheels
turning right, you want them to react the same way the right side wheels do
when you turn left (same relative balance in understeer/oversteer).
In the adjusted example weights originally given above, when the diagonals
are made equal, the left side has a 62%/38% F/R weight distribution, while
the right side has 64.3%/35.7% F/R distribution. While 2.3% may not be
enough to make a big difference in seat-of-the-pants feel, it is not
insignificant. It would be very possible that the car would push more in
one direction than the other, although possibly only a very sensitive
driver would notice it.
There is a corner balancing spreadsheet available at
http://www.356racing.com/balance.html which will calculate the ideal corner
weights for you according to Puhn's formula. All you do is fill in the
existing, measured weights for each wheel.
HTH,
TT
-------------------------------------------
Tom Tweed email: tweedt@ucsd.edu
La Jolla, CA or tweedt@rennlist.com
http://members.rennlist.com/tweedt
Proud to be a founding member of Porschelist and Rennlist
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