This spreadsheet published on the Elite forums (https://forums.frontier.co.uk/showthread.php?t=98061&p=1523008) shows the shield strengths for various classes. The figures are fascinating.
For instance, the Clipper class 7 "A" rated shields are 198MJ, but the Python can achieve better (213MJ) with a Class 4 "C" rated shield generator!
Quote from: Mike Evans -Designer Elite: DangerousThe ship itself defines the base shield strength however so typically as ships get bigger their base strength goes up. Also a larger ship might end up with a lower total shield strength than a smaller ship but when receiving damage the larger ship will nullify a lot of the damage from smaller weapons where as the smaller ship wouldn't.
See original spreadsheet here (https://docs.google.com/spreadsheets/d/1LhGGt9y0ga5HiV1tZL6k-hx4U_fIWY0IHES69Lc317U/pubhtml?gid=2011892275&single=true).
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