[electro wrks]

If I remember from my basic aerodynamics training, for stability, you always want the center of mass ahead of the aerodynamic center. This applies to aircraft, rockets like the new Spacex Starship, and motorcycles, particularly with dustbin type fairings, like this one. One advantage with electric bikes is that the batteries can be easily moved around to adjust the center of mass. Notice the batteries shifted to the front of the lower battery box. I'd be worried riding this bike if I raised my head up at the wrong time, the aero center might shift in front of the center of mass and cause stability issues! Have you noticed any problems with this?

Great job on a what looks like a fun project.

 

[electro wrks]

Good catch! The batteries are actually heavier in the rear of the box, with three of our five strands rear and two front. The extra volume in the front of the box is for the BMS stack, disconnect, connectors, and buttons. Based on what people told us of the friction coefficient, we thought we'd be traction limited to around 145mph with fairings. When we significantly exceeded that, we found the Cp estimation was off. We added more trail and shifted our ballast to the front of the bike to compensate and never had any issues after that.

What did you use for ballast, where is it located, and how much did you use?

 

[electro wrks]

Yes, but if the centre of aerodynamic pressure is too far behind the centre of mass, it is apparently difficult to control the vehicle - to make it turn if you need to. One of the fully streamlined two-wheeled entrants at Speed Week made a video about that.

Yes brian, you do not want to overcorrect a problem and then create another problem. The main task at Bonneville, AIR, is to point your vehicle in a straight line and try to keep it that way for the whole speed run. Unless, coleastering, you were on some kind of slalom course.

But the battery is also bulky, and tends to fill almost all available space, so it can be hard to move much. There is likely more room to move the relatively dense engine in a conventional vehicle.

Do you mean an ICE vehicle as a "conventional vehicle"? In my crazy ICE car days, the first thing we usually did to improve the balance of the vehicle, was to move the 12V battery to the trunk. It sure was a lot easier than moving the engine! In a relatively open structure, like coleastering's bike, it would be very easy to move portions of the battery to different locations. Or, even easier to move ballast around, as he apparently did, to improve the straight line performance.

 

[electro wrks]

In most production EVs the battery would be even more difficult to shift in position for competition use than the engine would be in an ICE-powered vehicle...

I think the veracity of that statement is too dependent on the engine and battery placement in a given vehicle. How am I going to shift the engine/transaxle around in a front wheel drive vehicle? Move it to the rear? Yeah, that's going to be easy to do. I could open a sub floor battery box, leaving some battery modules in the box, and pull out some to place them in a better location for a particular vehicle. brian, you are just thinking in too narrow of a range of possibilities.

... but of course we're not talking about a production bike here.

No, we are not. And, this is primarily a DIY forum, as you have reminded me in the past. It would be a good idea for the DIY builder to, if possible, have some provision(s) for adjusting vehicle balance, if a problem should arise. The batteries being quite heavy, seem to me to be a good candidate for doing this. If you have front and rear battery boxes, maybe have provisions to shift modules between the two to correct a steering issue. Maybe your battery box doesn't take up all of the available space. Maybe it could be shifted back and fore to correct a problem. Again, you need to think outside of the box! Or, between the boxes! Or, in shifted boxes!