Video analysis showed that the inside tire was lifting during hard cornering. Symptoms were mid corner and exit understeer. This led to research to determine the roll rate of the rear suspension through vehicle dynamics and spring rate calculations. Then, commercially available rear anti roll bars (ARB) were assessed and their spring rates calculated and compared to custom original designs. In the end, due to lack of manufacturing ability and time, the commercially available rear ARB was purchased and installed. Results: mid corner understeer corrected, exit understeer improved, vehicle cannot lift inside front tire.

1. MGB Roll Rate Issue and
Resolution
IUPUI Motorsports Engineering Program

2. Issue: Rear roll rate unknown causing front inside tire to lift,
leaving the ground during hard cornering and causing mid
corner to exit understeer.
No rear ARB installed.
Video Link: https://youtu.be/iOaa-F6FVi8

3. Video Analysis
• Through the use of video editing software the video was able to be
slowed to a frame by frame extreme slow motion.
• This allowed for the students to see that in fact the inside tire was
leaving the ground
• Attention should be paid to the shadow of the tire and the amount of
sidewall deflection for evidence of tire lift

4. Leaf spring calculations
Leaf Width # of Leaves Thickness of Leaves Main Leaf Length Rate
1.77 7 0.22 43.5 133.56
1.77 6 0.22 43.5 114.48
1.77 5 0.22 43.5 95.40
1.77 4 0.22 43.5 76.32
False
Leaf Width # of Leaves Thickness of Leaves Main Leaf Length Rate 1 Leaf at end Rate 2 Leaves at end Number of Leaves at end Modulus of Elasticity (PSI)
1.77 7 0.22 43.5 17.17255047 18.31738716 1 30000000
1.77 6 0.22 43.5 14.88287707 16.02771377 2
1.77 5 0.22 43.5 12.59320368 13.73804037
1.77 4 0.22 43.5 10.30353028 11.44836698
𝑘 =
2 +
𝑛
𝑛
𝐸𝑛𝑏𝑡3
6𝑙3

5. Research
• After researching what rear ARBs were commercially available and
obtaining pertinent information, calculations were performed to find
the spring rate of the available ARBs.
• Not pictured, vehicle dynamics to determine the roll rate by geometry
and leaf spring rate

6. Sway Bar Rate Calculations
Hollow Bar Fomula Solid Bar Formula
Current Rates
Hard Setting Soft Setting
Front Bar: 448.9383 New 1" Front Bar Rate: 691.4582 564.1033
Rear Bar: 208.4121
New front Hollow bar Old front solid bar
Rear Bar Calculations with Full Hollow Tube
Hard Setting Soft Setting G 11.5*10^6
OD: 1 ID: 0.75 450.2731 G 11.5*10^6 11.5*10^6 L 24.5
ID: 0.625 558.1778 L 28.1875 28.1875 d 0.875
ID: 0.5 617.5173 D 1 1 R 7.75
ID: 0.375 645.6594 d 0.625 0.625
R 7 7.75
OD: 1.25 ID: 0.75 1399.706
ID: 0.625 1507.611
ID: 0.5 1566.95
ID: 0.375 1595.092
OD: 1.5 ID: 0.75 3126.181
ID: 0.625 3234.086
ID: 0.5 3293.426
ID: 0.375 3321.568
Rear Bar Calculations with 14" Hollow Tube
OD: 1 ID: 0.75 739.7344
ID: 0.625 917.0064
ID: 0.5 1014.493
ID: 0.375 1060.726
OD: 1.25 ID: 0.75 2299.517
ID: 0.625 2476.789
ID: 0.5 2574.275
ID: 0.375 2620.509
OD: 1.5 ID: 0.75 5135.87
ID: 0.625 5313.142
ID: 0.5 5410.628
ID: 0.375 5456.862
𝐾 =
0.098 ∗ 𝐷4
− 𝑑4
∗ (𝐺)
(𝑅2)(𝐿)
𝐾 =
0.098 ∗ 𝑑4
∗ (𝐺)
𝑅2 𝐿

7. Resolution
• Due to limited time and manufacturing capability a commercially
available bar was chosen
• Results : Initial turn response was crisper, mid corner understeer was
corrected, corner exit understeer was improved but not corrected in
total. The vehicle cannot lift the inside tire after installation of rear
ARB.