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
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. Traction 67 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. Ground Force Lift/ Downforce 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 Centrifugal Force LR Traction Force RF 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= Traction force C f =T f C f =a*m=m*v 2 /r T f =m*µg c v 2 /r*m=m* µg c g c =9.81m/s 2 r=13.2m v=15.29m/s v 2 /r =µg c µ=v 2 /(r*g c ) µ=1.8 T f =1.8g c 9
Lateral Acceleration Comparison Lateral G-Force 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 Ford F-150 Ford Explorer Toyota Camry Porsche 911 Ford Mustang Ferrari Enzo Quarter Midget 0 Ford F- 150 Ford Explorer Toyota Camry Porsche 911 Ford 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 4 th setup is balanced, and the 5 th 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 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 6.25 6.2 6.15 6.1 6.05 6 Setup 1 (Left) Setup 2 (Right) Setup 3 (Front) Setup 4 (Distributed) Setup 5 (No Weight) Setup 6 (Left, Control) 5.95 11 12 13 14 15 16 17 18 19 20 Lap 13
8 7 6 5 4 3 2 1 0 Frequency Plot 14 Bin 5.98 6 6.02 6.04 6.06 6.08 6.1 6.12 6.14 6.16 6.18 6.2 6.22 6.24 6.26 6.28 6.3 6.32 More Lap Times (sec) Setup 1 (Left) Setup 2 (Right) Setup 3 (Front) Setup 4 (Distributed) Setup 5 (No Weight) Setup 6 (Left/Control) Frequency
6.2 6.15 6.1 6.05 6 5.95 Average Lap Times 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. 15 Setup 4 (Distributed) Setup 5 (No Weight) Setup 6 (Left/Control) Setup 3 (Front) Setup 2 (Right) Average Lap Time (sec)
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=mr 2 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 16
Average Lap Times vs Percent Rear Weight 6.18 6.16 y = -0.5002x + 6.387 R 2 = 0.2394 Average Lap Time 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 6.16 6.14 6.12 6.1 6.08 6.06 y = -0.001x + 6.1148 R 2 = 0.0175 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 6.16 y = -1.2156x + 6.8105 R 2 = 0.9247 6.14 Lap times 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