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The Effect of Weight Distribution on a Quarter Midget

Joey Dille

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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.

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ProblemIn 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?

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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.

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Axial Force Balance

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.

67

Traction

Drag

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Vertical Force Balance

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.

Gravity

Ground Force

Lift/

Downforce

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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.

Centrifugal Force

LF Traction Force

RF Traction Force

RR Traction Force

LR Traction Force

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Traction Force for CarsWhen 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.

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Coefficient of Friction and Traction Force

Centrifugal force= Traction force

Cf=TfCf=a*m=m*v

2/r

Tf=m*µgcv2/r*m=m* µgcv2/r =µgcµ=v2/(r*gc)

µµ=1.8=1.8

Tf=1.8gc

gc=9.81m/s2

r=13.2m

v=15.29m/s

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Lateral Acceleration Comparison

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Ford F-

150

Ford

Explorer

Toyota

Camry

Porsche

911

Ford

Mustang

Ferrari

Enzo

Quarter

Midget

Car

Late

ral

G-F

orc

e

Ford F-150

Ford Explorer

Toyota Camry

Porsche 911

Ford Mustang

Ferrari Enzo

Quarter Midget

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Test SetupThe 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.

Location A Location B Location C Total

kg kg kg kg

Setup 1 16.3 16.3

Setup 2 16.3 16.3

Setup 3 16.3 16.3

Setup 4 4.6 4.0 7.6 16.3

Setup 5 0.0

Setup 6 16.3 16.3

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ProcedureProcedure:

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

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Lap Times

5.95

6

6.05

6.1

6.15

6.2

6.25

6.3

6.35

11 12 13 14 15 16 17 18 19 20

Lap

La

p T

ime

in

Se

co

nd

s Setup 1(Left)

Setup 2(Right)

Setup 3(Front)

Setup 4(Distributed)

Setup 5(No Weight)

Setup 6(Left, Control)

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Frequency Plot

0

1

2

3

4

5

6

7

8

Bin

5.9

8 6

6.0

2

6.0

4

6.0

6

6.0

8

6.1

6.1

2

6.1

4

6.1

6

6.1

8

6.2

6.2

2

6.2

4

6.2

6

6.2

8

6.3

6.3

2

Mo

re

Lap Times (sec)

Fre

qu

en

cy

Setup 1(Left)

Setup 2(Right)

Setup 3(Front)

Setup 4(Distributed)

Setup 5(No Weight)

Setup 6(Left/Control)

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Average Lap Times

5.95

6

6.05

6.1

6.15

6.2

Setup 2

(Rig

ht)

Setup 3

(Fro

nt)Set

up 4 (D

istr

ibute

d)

Setup 5

(No W

eight)

Setup 6

(Lef

t/Contr

ol)

Avera

ge L

ap

Tim

e (

sec)

F Ratio (4,45) my data=13.69

F Ratio (4,45) Alpha=.01 3.78

Therefore there is a 99% chance that the change was not due to

natural data variation.

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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

Added Weight and Moment of Inertia

Location A Location B Location C Total Percent Percent Moment of Inertia

kg kg kg kg Left Rear kg-m^2

Setup 1 16.3 16.3 61.92% 60.69% 2.2

Setup 2 16.3 16.3 54.43% 55.43% 1.9

Setup 3 16.3 16.3 56.89% 51.30% 8.6

Setup 4 4.6 4.0 7.6 16.3 57.75% 55.25% 12.7

Setup 5 0.0 56.74% 60.92% 0.0

Setup 6 16.3 16.3 61.92% 60.69% 2.2

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Average Lap Times vs Percent Rear Weight

y = -0.5002x + 6.387

R2 = 0.2394

6.04

6.06

6.08

6.10

6.12

6.14

6.16

6.18

50.00% 52.00% 54.00% 56.00% 58.00% 60.00% 62.00%

Percent Rear Weight

Avera

ge L

ap

Tim

e

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Moment of Inertia versus Lap Times

y = -0.001x + 6.1148

R2 = 0.0175

6.04

6.06

6.08

6.1

6.12

6.14

6.16

6.18

0 2 4 6 8 10 12 14

Moment of Inertia (kg-m^2)

Av

era

ge

La

p T

ime

(s

)

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Average Lap vs Percent Left Weight

y = -1.2156x + 6.8105

R2 = 0.9247

6.04

6.06

6.08

6.10

6.12

6.14

6.16

6.18

54% 55% 56% 57% 58% 59% 60% 61% 62% 63%

Percent Left Weight

La

p t

ime

s

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ResultsThe 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.

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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.

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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.