via : www.twnclub.ch
Here are some scans and pics from Mark Frei, who imported the only Ariel HT5 back in 1958 and was competing in trials and enduro Swiss championship.
The Ariel Trials version was developped from the Red Hunter series and was commercialised 1956-59. There were 2 versions available: HT5 with 500ccm and HT3 with 350 ccm. The weight was claimed at 132 kg (dry without liquid). This was clearly ahead of the 150kg of a 350ccm AJS. There was no lighter and more powerful 4 stroke trials bike around. Front wheel was 21 and rear 19(!), ground clearance about 22 cm.