Roth in Germany is the biggest long distance triathlon in the world and will feature five of the top six from last year’s Ironman World Championships.
Lewis is providing regular updates of his training and racing on his YouTube channel.
Talking of Roth, he said: “It’s just a good opportunity to see where I’m at, see how I compare, what I need to work on, take those learnings.”
One of his ambitions is to be among the leading contenders as they tackle Solar Hill, where screaming spectators line either side of the road.
His racing has been more consistent than at the same period last season.
On Sunday Lewis was third in Challenge Wales.
He led out of the water in 24:13, nearly a minute ahead of his closest rival.
By the halfway point of the bike, the Isle of Man’s Will Draper had ridden through the field from 14th to lead, eating up a two minute advantage that Lewis had held.
As they hit T2, Draper was 20 seconds up on Lewis, with Harry Palmer a further 1:30 back.
After they had completed the first three laps, Palmer had run up into second.
Lewis was now nearly a minute down on Draper.
As they headed out onto the final lap, Palmer had taken the lead and was just under two minutes ahead of second place Draper.
Lewis had dropped off the pace, over three minutes down in third.
Palmer took his first professional win in 3:56:12, followed by Draper in second in 3:59:45 and Lewis in third in 4:00:42.
Lewis is in a race heavy stage of his training.
On 19 May, Lewis was 10th in Challenge Samorin and a week later finished sixth at Ironman 70.3 Kraichgau.
Between 21 and 23 June he will tackle the Long Course Weekend in Wales which simulates a full distance event, but split over three days. There will be a 2.4mile swim on the Friday, a 112 mile bike on the Saturday and a marathon on the Sunday.