How Fast Can an FJR-1300 Accelerate?

[Motorcycle Mayor]

I won't claim this write-up I did is definitive (or even correct ). But I hope you enjoy reading it as much as I had putting it and the Excel model it's based on together.

https://pursuit.olbert.com/2021/06/bring-the-antimatter-injectors-back-online-and-rig-for-warp-drive/

- Mark

 

[sullivan]

Good reading. Thanks.

 

[Motorcycle Mayor]

BTW, I updated the files and images on that post because I realized the dynamometer data I was basing everything on were measure at the wheel and not the crankcase (which makes sense since you'd have to disassemble the bike to measure it at the engine). So my applying a drive train loss factor (25%, as I recall) was double-counting the power loss.

Bottom line (assuming I'm correct) you can pull about 1 gee of horizontal acceleration in first gear running flat out. Which ain't bad

 

[wfooshee]

Where did you get that engine torque curve? Something on the web, your own dyno runs, what?

You had some fun, but you didn't consider aerodynamics, I don't think. None of those acceleration figures would actually be reached, being calculated with no drag. The acceleration curve you show has the upshift to 6th at pretty much at or even above the bike's aero-limited top speed, but with aero drag, the bike is not accelerating that hard at that speed.

I've seen that acceleration by gear chart called a cascade, but I've seen it presented as measured rear-wheel torque on the Y-axis rather than acceleration. I know you were looking to find actual acceleration figures, but that had to be calculated, based on some assumptions, in turn based on your torque curve (which you don't show a source for.) Once you have the rear-wheel torque for each gear, chart that against road speed on the X-axis, and where one gear's curve meets the next gear's is you ideal shift point regardless of aero load.

I know your objective was to see how hard the bike was pulling, but if that were actually measured in a real drag-race run, it would be lower than your calculations, I'm pretty sure. Knowing which gear to use by RPM would be more accurately determined by plotting against known torque rather than calculated acceleration.

 

[Motorcycle Mayor]

I got the torque curve from the web, a dyno run by a testing outfit for an article in some riding magazine.

I think you missed the disclaimer in the post . You are of course correct that things like air resistance aren't included. Not to mention the contact patch friction being broken by the application of too much force .

For anyone reading this thread and thinking "Cool! I can just jump on my bike and get to X speed in Y seconds"...your mileage may vary. In fact, it >>will<< vary, and on the downside (as in, the figures shown won't be met).

It'd be interesting to see some empirical data on acceleration. I haven't come across such online, although I didn't look particularly hard for it.

 

[hppants]

I enjoyed the write up, and took it in the spirit for which it was written.  The FJR's torque curve is very flat.  The motor is designed (and overwhelmingly hasn't been changed in almost 20 years) to haul the load and pull fairly evenly across the (relatively) short powerband.  

But Walter's comment can't be understated.  The aerodynamic drag's effect on acceleration and top speed is HUGE.  And that curve (drag v/s speed) is parabolic.

The butt dyno lies like a rug.