Bullfrog said:
Can anybody tell me the head tube angle of a stock Sur Ron?
Per sur-ron.ro/.it/etc its 26deg (= 64deg in common head angle terms)
https://sur-ron.ro/project/light-bee-x/
https://www.aebikes.com.au/specifications.html
But there have been a couple different forks on the front (26 & 27.5) so who knows which that was measured with.
W/ the 1260mm spec wheelbase, every 1mm increase in axle height = asin(1mm/1260mm)=0.045deg.
From the stock tire, the difference was about 35mm radius = ~1.6deg => 64-1.6=62.4 (that is if I *ONLY* put a bigger front tire on)
Going to a Fox40 27.5 fork was ~15mm longer axle crown measurement than my orig 26" RST. That's roughly equivalent to 15mm*sin(64)=13.5mm lift = another 0.6deg => 62.4-0.6=61.8
Since I ALSO used a larger rear tire, the front radius only raised ~7mm => 0.3deg. So my total change is only 64-0.3-0.6=63.1. FWIW, both my KTMs (150 & 500) are 63.5deg. I've never measured the ACTUAL angle but the bike steers ok but not super quick. I've used it on the scouting lap for a trials competition and its definitely 'lazy' compared to those. I really haven't ridden it and the 150 hard back to back to know if I can even tell the difference between the two. I've thought about ordering the rear shock link that lifts the rear a little and see if I like it. I'm tall and can use all the height I can get. But I'm close to making the bike too tall for my wife to ride comfortably so I have to tread carefully if I want her to ride along w/ us.
(Someone please check my math to make sure I didn't screw up.)