Yuba Kombi + Virvolt 900 - a trip review

Editor's note: another dictated¹

Last September or October we bought a Yuba Kombi and we took it to a bycicle repairman to install a Virvolt 900, which is a 691Wh battery and a 80Nm, 36V motor. This is slightly above the usual sizes you can find around, but the bicycle is quite heavy: it has the feet rests for the kids behind, plus the monkey bars, plus the seat for the youngest and a basket in the front, which is quite big. We have 24Kg for the bike, and then 3Kg for the motor and another 3Kg for the battery, excluding all the accessories.

Today I decided to take it for long spin. I've been using it for a while, but not for very long distances. Last weekend I took it almost to Callelongue, which is not that far: 20km way and back, with a pit stop at the supermarket for 2 full bags of groceries. It had less than a full battery and I had to return it with some juice for the next day, and it passed that non-test with good marks.

Today the trip was different: I wanted to have an idea of how much the battery lasts, and for that I selected a mixed trip, which includes mostly flat section, which is 34.5km long and only 240m of climb; and a quite steep one at the end, 9.2km long and 408m of climb. Technically I didn't choose that; what I choose is go to Sainte-Baume and I started looking at the routes that every router I had available. The first thing I noticed is that many of these routes were having a lot of uphill and downhill sections, ups and downs, ups and downs, which meant that there were several instances where every meter I gained I had to go down later and then go up again, which made no sense, specially since electric bikes do not have any type of energy recovery at all. If you spend energy twice or thrice to climb the same elevation meters, you are basically wasting it.

I remembered about BRouter, which is supposed to be a bicycle centered router, and start playing with it. I also watched a talk from five years ago where the author, Arndt Brenschede, explained that the only energy you have to think about is how much energy you lose due to friction against road and wind. I think he never explains it really well.

I chose the trekking bike profile, which was actually showing me some ups and downs, so I started picking at it, and I discovered that the profile was saying that going up had no penalty, and I thought that was wrong. In fact going down had a penalty of 60, which means that every 100m that you go down are equivalent to doing 6km flat. I say "well, if I want to penalize going up, then I just put a similar value for going up", and that gave me a route that was mostly flat and almost monotonically going up.

The trip²

Of course this is according to the data that these routers are using, which is mostly based on SRTM. This dataset has several issues, the first one being the resolution: it's only 30 meters, and that's 30 meters of longitude at the Equator, and 30 meters of latitude everywhere. I already discussed that the actual logitudinal resolution changes with latitude: every degree becomes smaller and smaller the closer you get to the poles, but I guess that's taken in account by the router. Even if it's a DEM, meaning it doesn't include trees and buildings, the level of detail for the road network can be really bad, and for ebikes and acoustic bikes, every meter counts.

On the way up I stopped several times: to buy some food; to eat said food, get some water and rest a little bit; to take some pictures, because to me that's part of going around. Everything was fine but I was getting really tired on the legs when I arrived to Saint-Zacharie, which is only 270 meters above sea level, right before the steep climb. So far I had mostly used level 2 out of five assistance levels, and gears between 7-9 out of nine gears, which is the same to what I use in the city when I'm alone. This is an assistive motor, not a pulling motor, so it only works when you work. That means I had almost constantly pedaled for 35km when I got to this part. I switched to using the lighter gears, between 6-3, and also using assistance levels 4 and 5.

When I reached Plan d'Aups I was not really tired; it was a fun experience under a really nice day. Then I decided to go down and I made one mistake, which was not taking the same route back home, but a shorter route that not only climbed 55m higher, it also had 80m of extra ascent⁶, for a total of 135m more than the original plan. I had only two bars out of five, and like many other electric vehicles, when this system gets to only one bar, it stops giving much assistance to save the battery from fully draining. My plug-in hybrid car does the same: when you reach the last 25% of the battery, it disables the full electric mode; at first it starts the ICE motor to charge the battery, then to drive the car, and there's no way to turn it off, even if you are close to your destination. I guess other cars would have this option if you used the internal routing system, but those maps are usually really crappy and outdated; or, if at least they're not out of date, it probably means it has a 4g chip that also sends a lot of telemetry home. That's a can of worms that I'll keep in the rack for a while.

I took the route down which was really fun, even if the bike is not the best for that. In particular, the wheels do not have road tires, but more like gravel tires with lugs. I think it lost a lot of energy in terms of friction the same way you can feel the difference between good asphalt from bad or old asphalt. Despite the steep descent, I could not make it go above 50km/h :)

When I reached Geménos I had only one bar³ and the system started to skimp energy, and that's when I got to the flats. I decided to save the battery so I turned the assistance off and start pedaling back home. It was still more than 20 kilometers away and I was really tired. I'm definitely out of shape for these kind of things; the whole trip was around 80km and 785m of climb, so something that I definitely could not do on an acoustic bike; I barely could with this one. Let's see tomorrow what my body says⁴.

From there the way back home was really slow. I stopped several times that allowed my legs to to rest a little bit, took a few pictures and finding directions, making sure I was getting the right road. I hit another issue: one of the roads that the router asked me to take was closed, and the only sensible option was to take another route that was going up 15m in some 300m. I was definitely very very very very very tired by then and my left knee started to hurt, so at this point I was being miserable and I still had more than 15 kilometers to go.

I made a few other stops, I bought a coffee and sweets in a bakery, and I just went back really really careful of what I was doing, taking every downhill section, and going at a pace that was not painful to me on every uphill section. It's a shame that my recording phone didn't work, the GPX would have showed how bad this was compared to being able to use the assistance, even when I was technically going down.

I'm now in the phase of preparing another testing trip: Clermont-Ferrand - Mont-Dore, some 45km +680m/+-380m⁶. My idea is to stop somewhere in the middle and try to recharge the battery, but the region is so sparsely populated that even finding a bakery, let alone a restaurant, means extending the trip for a few kms and +- meters. One route by the single restaurant I could find in the general direction adds 1.4km and +-120m; another, that goes by a charging station, adds 4.2km and and only +-30m, but this means having a snack, waiting in a parking, and going off the scenic road I wanted.

I have several rabbit holes I would like to go down and those include:

• Figure out whether I want a big bicycle like this or a smaller one but with smaller tires (I still want to carry two young children for a while). Smaller tires mean worse riding experience, specially since they don't have any suspension at all. But a lighter bike with the same system would have more range! One thing I know is that I'm not going to make this kind of trips with my kids. They're still young (almost 5 and 7yo) and they would get bored in the uninteresting or monotonic sections of the trip. It should also be a transitional bike; once they grow old enough, they would get their own bikes, but that's a few years from now.

• Could we collect GPS data to improve the data these routers use for ascent/descent/slope calculations?

• What router parameters make sense for ebikes⁵? I used my intuition to go against what the original developer decided, and they seem way more informed than me.

• What about buying an extra battery to extend the range and also as backup?

• Would commerces like restaurants, bars and bakeries allow or even offer recharging services, free or for a fee? I though of asking to recharge the battery at the bakery, but it was one of those chain things and it could have put the single employee in trouble. One thing is to recharge a smartphone, another is a 700Wh ebike battery.

I'll probably only check the first one, since I do want to buy a bicycle.