Mid Drive Isn't Adding Up

having now ridden a hub drive for a year and now a mid drive recumbent trike for a month or so (actually a front drive because the trike's bottom bracket is out front), I'm starting to get road experience of the benefits and problems of both.

One of the biggest claims made for mid drive is better centre of mass - bollocks. the rider is the largest and highest positioned mass on either an upright or a recumbent. Another factor in center of mass is rotational momentum, and here, a mid drive wins on an upright bike, bumps lift the mass of bike and rider through a shorter "lever." On a recumbent trike, a bump lists the mid drive through a short lever (the trike's wheelbase) vectored back to a lever longer than the trike's wheelbase by a factor of nearly 2, the distance between the pedal bracket and the back wheel. All the center of mass arguments for mid drive ignore the rider's mass and, again, on a recumbent, the rider's rorational moment is reduced but the mid drive's rotational moment is increased. I can clearly feel the differences between the two. Not to mention, all the rotational moments are complex, with torsional rotations due to the 2 front wheels rolling lines outside of the centreline.

On my "roady," the battery is a larger mass than the hub motor and, remove that, the bike rides beautifully, but rides like a truck with the battery. Battery position probably has more effect than the motor position. A factory built hub drive ebike, with a battery in the downtube will perform better than an ebike with a downtube battery and a mid drive because, again, as the front wheel rolles over a bump, that rotation has to lift rider, motor and battery for a mid drive, but only the battery and rider for a rear hub drive. The latter only hast lift the motor and rider, with less battery contribution, as the rear weel hits the same bump.

I've recently experienced my trike without the battery, and it rode over bumps more smoothly without the battery, even though it had about 4x the battery's mass in the panniers hung either side of the rear wheel. The battery is usually mounted just in front of the rear wheel, a very short lever pulled by a long lever, yet I could feel it more in bump shocks than anything the panniers contributed. I definitely want to move the battery cradle to the top of the rack and see how that improves the ride, because I think it may actually counterbalance the mid drive out at the end of the pedal spar.

Mid drive efficiency is often claimed. Because the motor applies its power where you do, to the chain, the claim is it uses less energy, because it doesn't have to work as hard in lower gears, but isn't this the point of e-assist? More torque when you can't supply enough.

There's a short, 3m climb up a gravel berm on a route I ride regularly. On my gravel bike, I get less front wheel slip from the front wheel (where the motor is) and feel more assistance from it than I get from the trike with its middrive. On the bike, my weight is shifted over the front wheel in a steep climb. I can feel the torque I'm applying to the back wheel and loose very little traction on the loose gravel, meanwhile, my front wheel gives me assistance I can genuinely feel and also loses no traction because of my forward weight shift. On the trike, the back wheel spits gravel, I feel like I'm doing all the work because the motor backs off when its 80Nm torque, geared down 3 to 1, starts causing slip and I'm left doing most of the heavy lifting. These are both 250w motors, the middrive providing twice the torque of the front hub, yet I feel the front hub doing its job and I barely can with the middrive, all the while spitting twice the gravel out from under my back wheel.

Where's the efficiency? In a drive control switching to a go slow? My gravel bike's front hub delivers 8Nm in a boost of 20% assist and I can feel it helping the second I switch it in. The middrive at 20% assist delivers 16Nm to the chain and there's no felt assist in any gear, despite there being a gear magnification of torque from 16 to 48Nm in my 36 tooth rear cog. If I pull the cheet button and don't pedal, it climbs alright, but the more I pedal, the less I feel at any setting.

I went e-assist because of my heart condition. I want exercise that doesn't push my heart rate above my safe limits, so I need to feel the boost when I ask for it. I don't want efficient boost, I want the boost that keeps me from cooking myself when the road rises. Felt but not smelled doesn't cut it.

To be fair, my 38km battery assisted trike and middrive uphill ride 3 weeks ago was easier than the same route, a week later, only downhill without a battery because I'd accidentally locked my battery inside my daughter's house. She wasn't due home until after dark and I needed to get home for apointments the next day. I had to ride. I say downhill, the route is 600m up with 200m down from Sunbury to the summit and, those 200m up and 600m down, it's the ups that hurt, not the downs. I managed the return to Sunbury OK, but I needed 2 full days taking it easy, so yes, the middrive helps. But efficiency isn't the be-all and end-all of electric assist. Feeling the assist is a motivation. Getting the rated torque at the traction point is more important, in an equity access context, than efficiency. I want range, but not at the expense of topping out my medically imposed MHR.

I feel like the majority of my range gains with the trike are down to recumbent posture, making cycling more a strength exercise and less so an aerobic activity, 3 wheels and go cart posture, reducing energy for balancing to the occasional posture shift in a fast corner, and lower wind resistance. The middrive is certainly super efficient, but I'm only "feeling" the assistance in how I feel at the top of a hill, not so much in a sense of reduced workrate for a given speed or climb. I'd really like to see what a rear hub drive does for me, especially a cadence sensing one rather than a torque sensing one, but that will have to wait for the warranty to expire for now.

And that reminds me of another problem with middrive, specific to a recumbent, boom suck, where the motor torque pulls the pedal boom shorter, no matter how tightly it's clamped. This is reduced by jamming a little PET cut from a soda bottle into the clamping surfaces, but the boom regularly needs resetting. In that respect, a rear hub motor wouldn't have this problem. At all.