Anyone remember thrust curves?

[Luddite]

I thought I'd start a new thread for this post rather than clutter up FrakenDesmo's http://www.ukmonster.co.uk/monster/s...d.php?p=573930

Originally Posted by Flip

It’s nice to know it reaches maximum revs reasonably cleanly but pressing on by revving it to 9k through the gears is kind of missing the point of the old 2v 900 as that’s way past peak torque which the wave you want to be riding to enjoy the bike at its best.

I'm with Flip on when to change up - the main thing that appeals to me about the 2v motor is that fat midrange. I really enjoy surfing that wave of torque and rarely venture past 6.5k.

Having said that, when I had my old S2R 1000, I made a point of finding out what the actual optimum gear change points were.

Now, who remembers the thrust curves that used to appear in service manuals back in the day and even some owners' manuals (that's when manuals used to contain useful information, not just an endless list of health and safety warnings!)?

They used to show the effective thrust applied at the rear wheel against the road at various road speeds in each gear and were designed to show the best speeds to change gears (in the days before revcounters were common).

Anyway, bearing in mind that the raw graph of torque at the rear wheel for the S2R 1000 looks like this:


Then this is what the resulting road thrust graph looks like for each gear:



You can see from these curves that the optimum gear-change point is where the curve for one gear intersects with the next. It is actually after the peak torque in any particular gear because, even though engine torque is dropping off in the lower gear, rear wheel thrust is still higher than that produced by the next gear for another couple-of-thousand revs.

So, despite the fact that peak torque is produced between around 5,500-6,200, rear wheel thrust in first is higher than that in second (for an equivalent road speed) until around 8,700, when second gear produces more and changing up is beneficial.

This is because of the multiplying effect of the various gearbox ratios, (the lower gear multiplies the engine's torque more than the higher gear), and it also explains why there's not one recommended shift limit for all gears.

Even knowing all that, as I said earlier, I still prefer to change up around the 6k peak torque - it just feels right.