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Mr Blair (67), of Pukerua Bay, near Wellington, said he decided on the 877km journey when his uncle Jack Knight (88), of Owaka, sent him a photo of his grandfather Eric Knight and his friend Frank Russell on a trip from Waipori to Nelson on Humbers in 1914.
''I thought: Oh, I'd like to re-create his journey,'' Mr Blair said.
His grandfather, aged 19, made the journey on his 1912 Humber motorcycle in eight days.
Mr Blair set off on his 1914 Humber motorcycle from Waipori at 9.30am yesterday and stopped in Waikouaiti for the night at 3.30pm.
The top speed yesterday was 55kmh and the average speed was 35kmh.
The gravel road from Waipori was ''violent'' to ride on, Mr Blair said.
He has postcards his grandfather sent during his trip. They talk of navigating uneven riverbeds and roads littered with horseshoe nails.
Mr Blair said the three-speed belt-driven motorcycle had a wooden brake, a foot clutch and a hand-operated gear change.
''Brakes on veteran bikes have nothing to do with stopping - they have got a little bit to do with slowing down - and you need a big pair of boots for the braking system.''
The hills of Dunedin were challenging and he was looking forward to the easy riding of the Canterbury Plains.
Engine: 500cc single cylinder
Gears: Sturmey-Archer three-speed in rear hub
Journey: 877km in six days
• Waipori to Waikouaiti: 111km
• Waikouaiti to Timaru: 157km
• Timaru to Christchurch: 165km
• Christchurch to Kaikoura: 199km
• Kaikoura to Blenheim: 135km
• Blenheim to Nelson: 110km