The Effect of Weight Distribution on
a Quarter Midget
Joey Dille
1
Background Information
A quarter midget is a type of racecar. It is similar to a
go-kart with several major differences, the most
conspicuous being the roll cage. I have a quarter
midget that I race on an oval track every Saturday
during the racing season.
2
Problem
In order to keep racing fair, the combined weight of
each car and driver in my class has to meet or
exceed a minimum weight requirement after the
race. To make minimum combined weight, I must
add 16.3 kilograms. I can add this weight to any part
of the floor pan.
How does weight distribution affect the
speed of a quarter midget?
3
Hypothesis
If the weight is more evenly distributed,
then the car will have the potential to
go faster.
Why? Racecars have balanced weight
distributions. A balanced setup makes
all tires work evenly and lowers the
stress on them when cornering. This
means more traction and better lap
times.
4
While a car is in
motion, many
forces are acting on
it. Here is a
diagram of a car
that is neither
accelerating or
decelerating and
moving in a
straight line.
Traction
67
Axial Force Balance
Drag
5
Vertical Force Balance
Gravity
This is a drawing of a car
from the back. The
force of gravity is
sticking it to the
ground. The ground is
exerting an equal force.
There are also the
forces of lift and
downforce. However,
they have very little
effect because the car
is not very
aerodynamic and isn’t
moving fast enough to
generate any effective
force.
Lift/
Downforce
Ground Force
6
Lateral Force Balance
This car is going around
a turn. Centrifugal force
pushes the car outward.
Centripetal force
counteracts this by
pushing inwards. The
centripetal force is
represented by the
traction force, which is
the force of the tires. If
centrifugal force
exceeds the traction
force, the car will skid.
LF Traction
Force
RF Traction
Force
Centrifugal
Force
LR Traction
Force
RR Traction
Force
7
Traction Force for Cars
When a car rounds a turn, it counts on its tires and
suspension to give it traction. A good test is to run a
car around a skidpad. A skidpad is a circular track.
The driver has to balance speed with control to keep
the car from spinning off the road. I used my track,
which is just an elongated circle, as a skidpad. From
this, a lateral g force is calculated. G-forces are
published in performance tests or car reviews.
8
Coefficient of Friction and
Traction Force
Centrifugal force=
Cf=Tf
Cf=a*m=m*v2/r
Tf=m*µgc
v2/r*m=m* µgc
v2/r =µgc
µ=v2/(r*gc)
µ=1.8
Tf=1.8gc
Traction force
gc=9.81m/s2
r=13.2m
v=15.29m/s
9
Lateral Acceleration Comparison
2
1.8
Lateral G-Force
1.6
1.4
Ford F-150
Ford Explorer
Toyota Camry
Porsche 911
Ford Mustang
Ferrari Enzo
Quarter Midget
1.2
1
0.8
0.6
0.4
0.2
0
Ford F150
Ford
Explorer
Toyota
Camry
Porsche
Ford
911
Mustang
Ferrari
Enzo
Quarter
Midget
Car
10
Test Setup
The extra weight in my car is there to make
minimum weight for my class and has a
mass of 16.3 kgs. I chose three locations to
place the weights-A, B and C. The weight is
normally placed in position A, making it the
control. The 4th setup is balanced, and the
5th setup has no weight added. Setup 6 was
used as the control.
Note: All the tests were done on the same day
with the same chassis and engine settings.
Setup 1
Setup 2
Setup 3
Setup 4
Setup 5
Setup 6
Location A
kg
16.3
Location B
kg
Location C
kg
16.3
4.6
16.3
4.0
16.3
7.6
Total
kg
16.3
16.3
16.3
16.3
0.0
16.3
11
Procedure
Procedure:
1. Record and document weight distribution with 4
different weight placements
2. Set MyChron beacon to trigger lap timer
3. Fill with gas
4. Put weights into car in configuration 1
5. Run 20 laps and record last 10 laps
6. Repeat steps 4-5 for every configuration
7. Organize data through project
12
Lap Times
6.35
Lap Time in Seconds
6.3
Setup 1
(Left)
6.25
Setup 2
(Right)
6.2
Setup 3
(Front)
6.15
Setup 4
(Distributed)
6.1
Setup 5
(No Weight)
6.05
Setup 6
(Left, Control)
6
5.95
11
12
13
14
15
16
17
18
19
20
Lap
13
Frequency Plot
8
Setup 1
(Left)
Setup 2
(Right)
Setup 3
(Front)
Setup 4
(Distributed)
Setup 5
(No Weight)
Setup 6
(Left/Control)
7
5
4
3
2
1
More
6.32
6.3
6.28
6.26
6.24
6.22
6.2
6.18
6.16
6.14
6.12
6.1
6.08
6.06
6.04
6.02
6
5.98
0
Bin
Frequency
6
Lap Times (sec)
14
Average Lap Times
F Ratio (4,45) my data=13.69
F Ratio (4,45) Alpha=.01 3.78
6.15
Therefore there is a 99% chance
that the change was not due to
natural data variation.
6.1
6.05
6
6
Se
tu
p
Se
tu
p
5
(L
ef
(N
o
t/C
W
ei
on
tr
ol
)
gh
t)
ed
)
ib
ut
(D
is
tr
Se
tu
p
4
3
Se
tu
p
2
(R
ig
(F
ro
nt
)
ht
)
5.95
Se
tu
p
Average Lap Time (sec)
6.2
15
Weight Analysis
I weighed the car using four scales so I could calculate
the percentage front and rear. I also calculated the
Moment of Inertia of the added weight. Moment of
Inertia is the resistance of the car to turning due to
the placement of the weights. I=mr2
Setup 1
Setup 2
Setup 3
Setup 4
Setup 5
Setup 6
Location A
kg
16.3
4.6
16.3
Added Weight and Moment of Inertia
Location B
Location C
Total
Percent
Percent Moment of Inertia
kg
kg
kg
Left
Rear
kg-m^2
16.3
61.92%
60.69%
2.2
16.3
16.3
54.43%
55.43%
1.9
16.3
16.3
56.89%
51.30%
8.6
4.0
7.6
16.3
57.75%
55.25%
12.7
0.0
56.74%
60.92%
0.0
16.3
61.92%
60.69%
2.2
16
Average Lap Times vs Percent Rear Weight
6.18
y = -0.5002x + 6.387
R2 = 0.2394
Average Lap Time
6.16
6.14
6.12
6.10
6.08
6.06
6.04
50.00%
52.00%
54.00%
56.00%
58.00%
60.00%
62.00%
Percent Rear Weight
17
Moment of Inertia versus Lap Times
Average Lap Time (s)
6.18
y = -0.001x + 6.1148
R2 = 0.0175
6.16
6.14
6.12
6.1
6.08
6.06
6.04
0
2
4
6
8
10
12
14
Moment of Inertia (kg-m^2)
18
Average Lap vs Percent Left Weight
6.18
y = -1.2156x + 6.8105
2
R = 0.9247
6.16
Lap times
6.14
6.12
6.10
6.08
6.06
6.04
54%
55%
56%
57%
58%
59%
60%
61%
62%
63%
Percent Left Weight
19
Results
The weight distribution in the car had a definite
effect on the lap times.
I found that there is a strong correlation
between lap times and the percent of left
weight. There is low correlation between lap
times and rear weight or Moment of Inertia.
My hypothesis was disproved. The car had a
greater potential to go faster when more
weight was placed to the left, as in setup 6,
the control.
20
Possible Errors, Improvements and
Applications
Possible errors: my performance as a driver may have
deteriorated near the end. Track conditions may also
have improved due to the rubber being added to the
track. Gas was being used up, so the weight was
decreasing slowly.
Improvements: Fill with gas before every run. Race on
an indoor track with no weather conditions. Run each
test a different day so I will be equally alert for each
run.
Applications: Any driver on a short, oval track could use
these results. Quarter Midget, Go-kart and quad
racers could benefit from this information. It could
give someone an edge in competition.
21
Weight Transfer
Weight transfer is the
movement of weight
to the outside of the
turn. This can cause
a car to skid if there
isn’t enough weight
on the inside of the
turn to counteract it.
For this reason, I
lean to the inside of
every turn.
22