This article is from the VW Performance FAQ, by with numerous contributions by Jan Vandenbrande others.
A:The SCCA defined several types of racing, open to the
"public":
Solo I is a high speed event, using cars prepared to road
racing safety standards; it covers both hill climbs and
race track based events. Solo I (and Solo II) are time
trials; there is no wheel-to-wheel action involved.
Solo II is a moderate speed event; it corresponds roughly
to what other clubs call autocross. Safety equipment is
not mandated, except for roll bars in heavily prepared
convertibles (stock convertibles do not require roll bars
in Solo II.)
 
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