Harley-Davidson seems to take an odd pride in its somewhat confusing model code lettering system, one where the same letter in a different position in the model designation can mean different things. Fortunately, within the early Sportster lineup, model codes are pretty consistent.
All OHV Sportsters from the beginning in 1957 carry the first letter designation X. Interestingly, this code had been used earlier for experimental models and also for the World War II shaft drive flat twin model XA.
The first, most basic Sportster should have been the model X. It’s speculated that the pre-production Sportsters had 6.8:1 compression and were in fact designated model X. But before production commenced, compression was raised to 7.5:1, so in line with Harley tradition the X became XL, the L meaning first level of tune (or, in the case of the Big Twins, extra displacement). The third letter was C for competition, or H for higher compression/second stage of tune; XLH meant the high compression/tuned engine in the street chassis, XLC meant a standard XL engine (maybe with magneto ignition) but the bike stripped for competition, and XLCH meant the high compression/tuned engine in the XLC stripped running gear. Well, for 1958, anyway. For 1959 the XLCH got its street uniform back, but retained the magneto. R was always for racing, and TT for that particular type of enduro-style competition. Confused? There’s a test later... MC