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Technical Information (MGB 4)

Composite Leaf Springs

Last Modified - 01/28/03

MGB Anticipated Ride Heights - MGB4(4)

During the development of British Automotive's composite leaf springs (over 10 years), we have installed and tested many of this type of spring. We have weighed countless vehicles and spent many hours trying to perfect this product. The final decision was to go with two spring rates 100# MGB Roadster and 135# MGBGT, available in both regular and low arch configurations. The composite springs that you purchase, when fitted to your vehicle will give an approximate rear ride height when measured from the center of the rear hub to the bottom edge of the rear fender molding. The measurement is entirely dependent upon the vehicle weight and weight distribution.

The latest test was carried out on a 1971 MGBGT which was independently weighed (KERBSIDE) and, based upon this information, new ride heights established for "chrome bumper" vehicles.

2306 lbs.
1156 LBS/1150 lbs.

Spring Rate

Left Rear

Right Rear

100# (114#) RA

100# (98#) LA

Difference (ride-ht.)


13 9/16"

12 1/2"

1 1/16"


13 3/4"

12 3/4"




135# (147#) RA

100# (139#) LA

Difference (ride-ht.)


14 1/8"

13 1/4"



14 1/4"

13 9/16"


From all of this information, it is possible to arrive at an approximate ride height for your vehicle, providing you know your vehicle's weight. For accuracy, we recommend that you weigh (KERBSIDE) your vehicle on an independent 4-wheel scale setup. For composite springs, subtract 30 lb. from your rear reading. Recommended ride height is 13 1/2 " (see "Suspension" article).

Testing for rubber bumper vehicles was conducted on a 1979 MGB Limited Edition.

2320 lbs.
1160 lbs/1160 lbs.

Spring Rate

Left Rear

Right Rear

100# (98#) LA

14 7/8"


To achieve the recommended ride height of 14 1/2" (see Suspension article), install 1/2" spacer blocks with the "Low Arch" spring as well as longer U-bolts.

We took the opportunity to measure the difference between "chrome bumper" and "rubber bumper" rear spring front mount and rear shackle mount eyes and we recorded a vertical increase of approximately 2."

For additional information select from one of the following categories:

MGB4...Composite Leaf Spring Overview

MGB4(1)...An Introduction to Composite Springs

MGB4(2)...MGB Vehicle Weights

MGB4(3)...MGB Vehicle Lean Problems

MGB4(5)...Marketing Update

MGB4(6)...General Installation Instructions

MGB4(7)...Rear Ride Height Adjustable Shackle Pin Kit

MGB4(8)...Rear Telescopic Shock Absorber Choices