Front Bias, Left Bias, and Cross Weight: Suspension Tuning with Weight Adjustments

Static Weight: Front Bias and Left BiasCross weight (AKA wedge) is slightly more
The most fundamental way of changing the handlingcomplicated. Front bias and left bias adjustments are
of your car is by redistributing the weight. Themade by actually moving components of the car
weight distribution of a car is determined by literallyaround to try to achieve the desired weight
placing a scale under each wheel. When makingdistribution (e.g. moving the battery to the left side
weight distribution adjustments, you must consideror rear of the car). Cross weight is adjusted by
the weight transitions that the car experiences whilelowering or raising the upper spring perches on each
you are driving. For example, when you accelerate,corner of the car to raise or lower that corner.
weight shifts toward the back of the car onto theTo understand how cross weight works, imagine a
rear wheels. When you turn right, weight shifts tocar that is perfectly level with the ground (equal ride
the left side of the car. You can feel these weightheight at each corner). If you raise the left rear
transfers on your body while you are driving.corner (increase cross weight), that corner now
The most useful weight adjustment for road racing iscarries more weight because it is sticking up. In
front bias, or the weight distribution between theaddition, the car is leaning towards the right front
front and rear wheels. The purpose of adjusting(trying to compress the right front spring) so that
front bias is to balance the weight of the car evenlycorner is holding more weight than it did when the
between the front and rear wheels while the car iscar was level. The left rear and right front hold more
turning. If the front tires have more weight on themof the weight of the car than the right rear and left
while turning, then they will have to exert more forcefront.
on the racetrack than the rear tires to keep fromIf you lower the left rear corner of the car, then the
sliding. The same goes for the rear tires. This can beleft front and right rear corners are sticking up more
seen from basic physics:than the left rear. Therefore, the left front and right
F = ma = (m * v^2) / Rrear hold more of the weight while there is less
F = Forcem = massa = accelerationv = velocityweight on the left rear. Since the left rear corner is
R = radiuslowered, the car leans in that direction, which also
It can be determined that the acceleration of antakes weight off of the right front tire. In summary,
object of mass "m" traveling around a circle of radiusby lowering the left rear (decreasing cross weight),
"R" with a velocity "v" is v^2/R, and the forcethe weight on the left front and right rear increases,
necessary to stay on the circular path with thisand the weight on the right front and left rear
velocity is just the object's mass multiplied by thatdecreases.
acceleration. Let's assume that your car has moreCross weight is usually measured as a percentage of
weight on the front tires than on the rear tires.the total weight of the car. Take the following
Looking at the formula above, we can see that massweight distribution as an example:
is the only thing that changes the force that the tiresLeft front: 750 lbs., Right front: 700 lbs.
must exert since the square of velocity and radiusLeft rear: 700 lbs., Right rear: 750 lbs.
are essentially identical for the front and rear of theThe cross weight is simply the left rear/right front
car. Therefore, since the front has more mass, the(diagonal) weight divided by the total weight of the
front tires will have to provide more force than thecar and multiplied by 100 to make it a percentage. In
rear tires to keep from sliding. Eventually, the frontthis case, the cross weight is:
tires will begin to slip before the rear tires, which is[(2 * 700) / (2 * 700 + 2 * 750)] * 100 = 48.3 %
the definition of understeer.Cross weight will not change left bias or front bias
Making the weight on the front tires and the rearweight distribution. Using the example above, you can
tires equal in a turn does not necessarily mean thatsee that front bias is 50% ((750+700)/(750+700)),
the weight distribution should be 50/50 (50% front,and left bias is also 50%. Assume you decrease
50% rear) while the car is standing still. The type ofcross weight to 46.6 % with the following settings
track you plan to drive on determines the ideal(while keeping total weight the same as before):
weight distribution. If the track requires getting onLeft front: 775 lbs., Right front: 675 lbs.
the throttle early in the turns, then weight will beLeft rear: 675 lbs., Right rear: 775 lbs.
transferred to the rear of the car while you are inThe front bias and left bias are both still 50%.
the turn. Therefore, you should add weight to theDecreasing cross weight adds oversteer to the car in
front of the car to offset the weight transfer whenleft turns. The front tires grip better since the left
you get on the throttle.front starts out with more weight than the right
Instead of using a 50/50 distribution, you might wantfront. In the turn, weight transfers from the left
to try 55/45. The front of the car will be heavierfront to the right front, which balances the front of
than the rear when the car is standing still, but whenthe car and maximizes grip. On the other hand, the
you accelerate in a turn, weight will shift to the rearrear of the car is not balanced in a turn. The right
and balance the car. If you are driving on a trackrear holds much more weight than the left rear.
with short, sharp turns, then you will probably beTherefore, the rear tires do not grip as well as the
getting on the throttle late in the turn. Therefore,front tires, which creates oversteer. With the same
you want a more even weight distribution to startkind of reasoning, you can see why increasing cross
out with (possibly 51/49) so that the weight will beweight creates understeer.
evenly distributed as you drive through the turn.Cross weight is usually difficult and time consuming to
Generally, if you are driving on a road coarse withadjust on a street car even if you have installed
approximately the same number of left and rightaftermarket suspension components such as
turns, front bias should be the only weightcoilovers. Unless you are building a pure race car for
adjustment that you work with. However, there areoval tracks, you don't have to worry about cross
two other adjustments that can improve handling ifweight adjustments. Remember that the weight
you will be racing on an oval or a track withdistribution of your car, particularly front bias, is the
predominantly right or left turns: left weight bias andmost fundamental characteristic that affects how
cross weight. Left bias is adding weight to the leftyour car handles. Keep in mind that the weight of the
side of the car so that it will be balanced in left turns.driver affects weight bias. Placing parts on the right
The same can be done for right turns.side of the car will help balance the weight of the
Cross Weightdriver on the left side.