Mahr is charging full speed ahead towards the starting line of Ironman Port Macquarie 70.3 in 2021 despite losing his eyesight to congenital toxoplasmosis.

During the race next year Mahr will cover a 1.9 km swim, 90km bike ride and 21.1 km run while tethered to guide Kevin Stringer.

Mahr, a two-time Sydney City2Surf finisher is already a regular sight on the streets of Port Macquarie running at Parkrun, cycling on a tandem racing bike or just out walking with guide dog, Shadow.

"Completing the half Ironman is something I've always wanted to achieve and something I never thought I'd do," said Mahr.

"I've done the 21.2km run before at the Forster Running Festival in October 2019 and I've just started training my swimming in the last three months.

"I like a challenge and this is a challenge (that's what motivates me).

"I say, where there's a will there's a way and you've just got to find it. Don't let life stop you."

In the last four years Mahr has dropped from 141 kilograms to 106 kilograms through exercising, nutrition and 'cutting out the junk'.

Mahr's training regime includes six hours of cycling with three hours of running and two hours of swimming a week. He also swims 2kms in fresh water, twice a week.

Mahr and Stringer have been cycling together since March in preparation for the Ironman event next year. Finishing the race will be a first for both men.

"We'll be swimming side by side connected by a tether and running with a waist or hand tether," Stringer said.

"He's taken on a committed approach to do this. I would challenge anyone without the visual impairment to do half the stuff he does.

"He's got more tenacity and commitment than anyone I've met. Many athletes have seen this coronavirus pandemic as an excuse to pull back but he sees it as a reason to work harder."

It hasn't all been smooth sailing after the pair were clipped by a passing car and trailer at the Port Macquarie donut in March. Stringer fractured his arm during the crash.

Mahr is planning to raise funds for Guide Dogs Australia closer to the event next year.

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