Advice for Electro Streetfighter build - CBR900RR conversion


1 µW
Jul 26, 2021
Hi Experts of the ES forums, and welcome to another noob’s mind-vomit! I bought a 1996 CBR900RR project bike with the intention of electrifying it (big bike holds more batteries, amirite?). I’ve been reading a lot online, including these forums, and I have started to plan my own build. I would appreciate any comments, criticism, sanity checks, or just questions regarding my planned build, especially from anybody who has done something similar or put serious thought into it.

I have a few degrees in engineering and have a buddy who has been building electric bicycles for decades. I’m reasonably handy (tire/fluid/filter changes, some carpentry and metal working), and have actual automotive and motorcycle mechanics nearby for emergencies. It won’t be easy but I believe this is something I can tackle, and I don’t expect this to be a quick or cheap endeavour.

My goal is to use the e-moto to commute and short trips in the countryside near where I live. Expected cruising speeds will be mostly 60-80 km/h, but I would like to be able to go on the highway (110 km/h ring roads, 5-15 km distances). We do have some highways where the limit is 130 km/h, but I don’t expect to have the distance to make use of those. That said, I’m aiming for a ~130 km/h top speed so I don’t have to 100% max out the motor on the highway, and have a little “get out of the way” buffer.

Desired range is 80+ km, enough to make a 60 km round trip with confidence. I haven’t done any distance calculations yet as I’m still trying to match currents/voltages between batteries and motors.

Bike curb weight is 203 kg, engine weight is ~66 kg. The bike is built to accommodate 2 people, so I’m aiming for a battery weight of roughly 66kg, plus motor, and can go a little past this without much stress (though some impact to handling).

Initially I was aiming at the QS 17inch 12kW DCBL hub motor, used in James Biggar’s custom build. However, I suspect I’d have to modify the rear swing-arm both in width and clamping points. Since my goal is to ride this on public roads, modifying the frame is a no-go (likely would not be able to register it). Plus I’d like to retain the option to use wheels of my choosing (paint, new rims) and hub motors restrict some freedom there.

My current motor choice is a ME1507 PMAC air cooled 14kW mid motor, with a 37/17 reduction. The spec sheet said 8000RPM max, but it also says 0.026V/RPM, and at 96V that’s roughly 3692RPM, which points to 138 km/h top speed. See the link to the Google spreadsheet for the math. Given the expected battery (up next) giving 600A max, I’d have a 0-100 time of 4s. One second slower than the CBR’s IC engine, but definitely not slow.

For mounting, I plan to get a custom welded (but not too heavy) steel frame that has mounting points for the batteries and motor, and bolt that to the engine mounts on the bike frame. I still need to map out dimensions.

I’m aiming for a 96V pack built from LiFePO4 cells, due to cycle lifetime and un-blow-up-ability (a word thrown around a lot these days). I’m foregoing building my own pack from single cylindrical cells and looking at larger rectangular 3.2V cells of 20Ah. 3P30S gets me 96V/5.76kWh/600A-max @ 58.5kg, while 4P30S gets me 96V/7.68kWh/800A-max @ 78kg. I guess I can start with the 3S30P and add another series pack if I find I lack the range. 78kg is bit heavy, plus a 21kg motor (est. 236kg curb weight, 33kg over ICE weight), but still lighter than most passengers.

While the pack above uses cylindrical cells inside, an alternative pack from the same manufacturer uses prismatic cells which get higher capacity (0.156 vs 0.098 kWh/kg) but lower maximum current (3.241 vs 10.256 A/kg) per unit mass. I’ve opted for lower capacity but higher peak current because I currently don’t think range will be an issue (based off comparison to James Biggar’s work, not my own calculations), and want to reach maximum acceleration.

Red Tape
A note on the least fun part of this: registration. I live in Denmark. The bike was imported from the UK (I have the papers) but never registered here. I’ve been told it will be easier to get the electric version registered if I get the ICE running and registered first, then convert it. I know frames (not engines) are what gets registered here, and that no modifications to the frame or load-bearing structure may be made (but engine swaps are totally legal). I’d like to go directly to electric and bypass tuning up a rough ICE for no other purpose than registering and tossing it. If anybody has tried something similar, even in a different country, I’d love to hear how it went.

That’s it?
For now. I was trying to wrap my head around how much performance I could get for my expected budget. Controller, contacts, converters, controls come on top of this in another budget, they will likely be constant regardless of the motor/battery combination.

If you made it this far, congratulations and thank you very much. And once again, any input on the beginning of planning for this build is very much appreciated.

Link to calculations sheet.

cbr900rr project.jpg