Have a think about where you want to go and what you want to do as well.
From Wairoa, you've got some great motorcycling roads within easy reach, like East Cape, Devils Elbow and if you're really adventurous, Waikaremoana.
I've ridden my VTR250 at a good clip around East Cape with no probs, and I'm a fairly "solid" chappie (actually, I'm a fat c**t). I've tried a GTR250 and it didn't feel like it had enough torquey grunt to get up the hills as quickly as the VTR.
An in line 4 will need a lot of gear shuffling to keep it hustling up the big hills around where you are, so a v-twin would be a go for lazy buggers like myself (actually you still do a lot of shuffling as opposed to a 600, but the extra torque makes relaxed riding easier).
With the big off road areas around you, I'm not sure what 250 trailies could fit the bill, but then you'd sacrifice sealed road speed and performance, but think of the fun you could have (check the MMMM adventure ride reports).
"Atomic batteries to power...turbines to speed..."
- Page 14 of the Buell Owners Manual
Bookmarks