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The number the 16-year-old is most concerned with is the amount of days he will be off his mountain bike.
from today until Sunday.
He is lucky to be lining up at the start line, given he is still nursing injuries from his last crash.
He broke his jaw "about a month ago" and has braces to prevent some very wobbly teeth from falling out.
"I've got a couple of fake ones in there and they just move about," he said.
"They are just attached to my braces and are just hanging there. That was a couple of nights in hospital."
The John McGlashan College year-12 pupil appears undeterred by the threat of injury.
Earlier this year a spill left him with two broken arms. He has previously broken his collar bone, his pelvis and his wrists more than once.
He was not able to give an exact total, shrugging off such questions.
Zach followed his father, Karl, into the sport about three years ago.
"It sort of snowballed from there," he said.
While he is entered in the cross-country and enduro, it is the downhill where he hopes to do best. He finished third in his grade last year and hopes to do as well this time.
The event has attracted about 350 riders. Most of those riders are from outside of the city, and 10 have travelled from the North Island to compete.
Competition starts this afternoon with the enduro. The downhill is being staged tomorrow and the cross-country has been scheduled for Sunday.
Mountain Biking Otago (MBO) has hosted the event for the last five years. Last year the championships attracted 179 riders.
MBO president Kristy Booth put the increased interest down to the growth of the sport and the fact the event has a good reputation.
"MBO is extremely proud of this event and the work we have done with Cycling New Zealand to develop it to this level," she said in an email.
"Signal Hill is an excellent venue as we can cater for all codes at the one venue and we have such a range of courses that we can change things up each year."
The South Island School Champs will be the first event following the development at Signal Hill, she said, adding the committee was excited to see how it works during the next three days.