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Technical Information (MGB 4)

Composite Leaf Springs

Last Modified - 01/28/03

Marketing Update - MGB4(5)

In the past British Automotive marketed 2composite spring sets 100#RA and 135#RA series. Thanks to customer feed back we now only supply the 135#RA series.

Another major reason was in the production tolerances. With a tolerance factor of + or - 15% during the manufacturing process, we could arrive at a range of between 85# and 115# for the 100# series, and 120# and 150# for the 135# series. Customer feedback dictated the need for the later than the former.

When we first started our composite spring project back in 1992, we were limited, in the manufacturing process, as to how much arch we could put into the spring blade, (approx. 5"). Having measured the arch on various new OEM steel springs, (approx. 6"), we concluded that the approximate 1" difference in arch would be ideal for performance minded MGB owners who, indicated that they would like to reduce their vehicle ride height, and therefore benefit from the improve handling characteristics.

For the record, we also experimented with lower arched springs, 100#LA and 135#LA (approx. 4.25") and concluded that these lower arch springs were impractical for street usage. Another concern was in the possibility of the spring blade reverse arching, especially under high load conditions when cornering. This reverse arching condition would be characterized as "falling rate"


Should you purchase a composite spring set which, results in the rear ride height being too high, British Automotive can supply you with 3 separate lowering block kits, ranging from 1/2" 1" and 1.5".

Information on this product can be found by accessing MGB31.


Conversely, should you purchase a composite spring set which, results in the rear ride height being too low, British Automotive can supply you with an adjustable ride height kit which, allows for increases in ride height ranging up to 1.25".

Information on this product can be found by accessing MGB4(7)


It is highly recommended that British Automotive's panhard rod assembly be installed along with your composite spring set. Installation of this product ensures that axle deflection, especially under cornering loads, will be eliminated, with the end result being a very positive rear end.

Since the panhard rod is designed to follow the horizontal centerline of the axle tubing, no change in roll center height occurs. British Automotive's design is mounted as low as possible without major fabricating or welding being required.

Further, installation of a panhard rod assembly enables the use of wider rim wheels and modern low profile tires without the associated body to tire contact problems.

NOTE: More information on the panhard rod is available by accessing technical article MGB15.

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(4)...MGB Anticipated Ride Heights

MGB4(6)...General Installation Instructions

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

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