just curious as to what you mean by 70mph not able to hang on to? I reckon the R65 is good to cruise for extended periods (4+hrs) at 6000rpm. Maybe the cooler temperatures in NZ help. I acknowledge it is a lot different from riding at lower revs that you get on a R100. But what do you let your R65 cruise at?
Please understand I am not dissing the R65, I love them and some of my best friends ride them.
BUT, to use a comparison, the R100RS will simply sit at any speed you select up to beyond 100mph and will maintain that speed up hill and down dale - effortlessly.
Herding the R65 along at high speeds involves constant winding on and off of throttle, even quite small hills will knock 10 to 15 mph off the poor things.
This is for a number of reasons.
Firstly the Carol Shelby reason, "there ain't no substitute for cubes baby."
Secondly the R65, particularly the post 81 R65s produce horsepower at the expense of torque, they have 50hp, the same as the R80, but the torque figures are quite different.
See
http://w6rec.com/duane/bmw/engine.htm fr some very interesting comparably figures.
By way of direct comparison - the 33km journey between two local towns (Mareeba to Atherton) is quite uphill (not that you would notice it) and really knocks the edge off the R65, particularly if you want to pass a slower vehicle. Whereas the wife's R65/80 has no such problems at all (valid comparison as it is an R65 in very respect except the engine) which just lopes along at any speed you want subject to the revs from the low R65 gearing. It is of note that the r65/80 has a heavy flywheel.
Thirdly wind gusts, buffeting from vehicles travelling in the opposite direction knock speed of the r65 - but this did not used to happen on the R60 and even the R50 i spent some time riding, the old airheads were more highly geared than the r65, but had a lot less horsepower, the difference I suspect was greater torque and better "persistence" due to the heavy flywheel.
Sidebar discussion of horsepower -v- torque:
Horsepower looks impressive, but torque is what does the work. An old old "R" model Mack from 1966 has around 250hp, yet the torque it develops allows it to pull loads that a modern sports car engine of twice the horsepower could not even begin to shift. (In case anyone doubts the veracity of that. I'll supply the R model Mack and a trailer with 50 tons on it, you supply the Ferrari F35 or Mclaren and we will see which one has the least difficulty in pulling a 50 ton trailer - you are welcome to change the sports car's final drive as much as you like (essentially a torque multiplying dodge).
So, my efforts to change the R65;s characteristics are to gear it up a bit and try and give it a little "persistence" in the face of transient loads by way of the heavy flywheel.
And if that doesn't work I'll just put a seibenrock 860 kit into it!
