To be honest its not so much the tare weight of any particular rider and bike thats the problem when it comes to speed although it does have some effect.
Its more a function of wind resistance.
For example - if I can get 35mph with an all up weight of say 200lbs in a sat up position (which is how I have to ride) and on an unfaired bike; I might get maybe 40 or so if I put a fairing on the machine and rode underneath or in line with the fairing. All in all the tare weight of the machine would have increased but the wind resistance would have reduced and that ultimately is what limits the speed of these machines.
However this is not the end of the story because you also have rolling resistance. This is a function of all the friction surfaces on the bike and drivetrain and also the friction losses from the tyres and such.
If the bike is well maintained or new and the engine kit and such are properly adjusted these will be minimised. So to with correct tyre pressures.
I am an avid reader and I remember reading my fathers new car manuals when I was a kid - just out of curiosity really (that and he could never set up the radio right - the news tended to be read by someone who sounded like a lemming on speed for about a week until I got tired of it and set it up right)- and they always had an advisory on tyre pressures - the Renault one was usually something along the lines of a loss in tyre pressure of only 4psi (32-28) would increase fuel consumption by 5% given the same driving method. When you consider that involved a vehicle with 123hp you can see how much of an effect it would have on something so much more marginal as one of our bikes.
All in all therefore, although tare weight is a function related to the speed you will manage given a particular rider/machine combination its much less important than wind and rolling resistance (hence why all the european car makers - with limited horsepower - made aerodynamically slippery designs from the late '70s - and the US still makes vehicles that look like someone put wheels on the garage, Dodge Ram & Caravan etc I am looking at you..)
I think you should be able to manage the speed you are aiming for without too much problem - even on a tight engine.. happy riding
Jemma xx
I do plan on getting the shifter kit though, maybe this will help. If I want to go faster I hop on the whizzer.
