3 ms·I've seen them on construction equipment, which admittedly moves very slowly.by seanp2k2 11y agoI've seen them on construction equipment, which admittedly moves very slowly.achamayou 11y agoThey get rather wobbly and noisy as you reach higher speeds.detaro 11y agoAre they actually open like that? Because with construction equipment I'd get worried about stones and stuff get stuck in there...