MGB Roll Rate Issue and Resolution

IUPUI Motorsports Engineering Program

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

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

Leaf spring calculationsLeaf Width # of Leaves Thickness of Leaves Main Leaf Length Rate

1.77 7 0.22 43.5 133.561.77 6 0.22 43.5 114.481.77 5 0.22 43.5 95.401.77 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 300000001.77 6 0.22 43.5 14.88287707 16.02771377 21.77 5 0.22 43.5 12.59320368 13.738040371.77 4 0.22 43.5 10.30353028 11.44836698

𝑘=[2+( �́�𝑛 )]𝐸𝑛𝑏𝑡3

6 𝑙3

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

Sway Bar Rate CalculationsHollow Bar Fomula Solid Bar Formula

Current RatesHard 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 barRear 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 1507.611ID: 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

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.