IMO, they used angled yokes because it was the cheapest way to achieve the desired trail,
after they changed the rake.
Rake is less important than trail.
Interesting read:
© Tony Foale. 2000-2018. (The experiments were conducted around 1982/83.) Rake The author’s ideas mentioned in other articles in relation to the angle of the steering axis (rake) were subsequently put to the test by modifying a readily available standard production machine – a BMW R75/5. There...
motochassis.com
But why didn’t they simply change the rake enough to achieve the desired trail? Presumably the required rake increase had underside side effects?
After my test ride today I’m totally convinced that Norton did what they did intentionally as a far more seriously thought out and deliberate intent than I had perhaps given them credit for. But I still do not understand the science behind how the two aspects of fork rake and trail changes interact, which was why I asked the original question.
Nevertheless, even without the desired knowledge, I tested the bike today on a route with a great little stretch for testing purposes, involving a fast stretch of road, with some mild inclined and declined curves with bumps and irregularities in the middle of these curves.
If Glen has a Dyno Hill… this is my Chassis Dyno…
The bike was very noticeably more stable. I did several runs trying different angles of attack and acceleration rates, plus steering damper settings, ending up with it totally backed off. Both during acceleration and sustained speed, even nudging 7,000rpm in top, it was totally stable and confidence inspiring. Previously, although this bike never ‘slapped’ it could be made to feel like it was on the verge of doing so (I know, totally subjective, but I could still ‘feel’ it).
I also fitted new clip ons that give approx 3” more total leverage. I mention this because I could not detect ANY increase in weight / feel to the steering at lower speeds at all. In fact I could not detect any negative effect whatsoever. My wife might suggest this is due to my insensitive nature (and she may have a point), but perhaps the increased leverage of the new clip ons countered any increased weight / force required for steering?
Whatever the science, (which I’d still like to know more of, so I’m currently reading John Robinsons book on chassis design) the clear conclusion from actual testing is that I will be sticking with the offset yokes.