Yamaha own a patent (US # 4,650,021)- it is basically the same as the experiment described in the JSAE (journal for the Society of American Engineers) paper published in the JSAE Review Vol.9. No.3, 28 May 1988.  Written by Atushi Matsuda (engineer), Toshiyuki Satoh (staff eng) and Akira Hasegawa (manager R&D), it came to light after I had finished my bike but it wouldn't have altered my design even if I had seen it first. It is less 'sophisticated' than my design- although it did have some interesting features.  They based their experiments on a standard bike - the patent sketches suggest it was an SR 185 - a god awful single cylinder chopper thingo. It was probably used as Yamaha couldn't sell them - a dealer friend of mine couldn't give one away he had on his floor.

They rigged up a single sided swingarm and fitted a universal to drive the rear wheel inboard of the sprocket. The 'kingpin' seemed to be fixed to the swingarm with zero rake - but varying with suspension travel – admittedly not much if it was a SR 185.   Lock was about +/- 15 degrees. The conventional front forks were used and an adjustable mechanism was set up to operate a push-pull cable to steer the rear wheel with a 'fixed' ratio (i.e.- no delay like mine) of the front steering lock. It was adjustable over centre - giving up to 40 % of front lock in 'bend steer' and 10 % of front lock in 'crab steer'.  A second test bike was made with double sided swingarm - this had 20 % both bend and crab steer. It used 2 tension cables for the steering.

	Getting really bizzare is another patent (US # 4,733,742) which is a 2 wheel steer & 2WD) amphibious vehicle, it even includes a roll cage ! It as no steer axis at all- it uses long axles that slide in slots in the frame (getting the idea?).  It also steers both wheels together and at the same angle so it would have no countersteer meaning it would be impossible to initiate a turn (let alone the fact that it has no rake or trail and therefore would not have any centreing of the steering).  Click the picture at left and also here to have a laugh at it... really bizarre!
	From the same 'inventor' comes US # 4,157,739, a similar device employing 2 normal headstocks. That the other one is an 'improvement' on this one says a lot!  Click here for details of the steering setup.
	Getting closer to reality is this design by James Parker US#5054572.  Those with a keen memory might remember James as the constructor of the RADD Yamaha FZ750 back in the 80's - the bike that spawned the GTS1000 alt-tech production bike.  This is an interesting design, perhaps a little complex, but none the less infinitely practical- especially after the previous two! :-)