Back when I worked for a GM truck dealer most of the tires I saw on the W4 and W5's (just rebadged Isuzu NPR's) had 17.5" tires on them. Like LRH said, they are very common on low cab forward trucks.[/QUOTE
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That must have been a few years ago; as now they jump from the 16" directly to the 19.5". I have seen a few older ones with the 17.5's, and see references for wheels occasionally. Must have scared some folks, so the US spec model Isuzu's (Japan built Diesels and US assembled 5.7/6.0 gasoline) no longer show them as standard, nor as an RPO. A local junkyard has an old wrecker chassis (GMC W4 or W5) with the 17.5,s. I have also noticed that UPS has used/specified them on some chassis. Nissan UD still spec's them for US.