Hi ebike people

tl:dr: what is one of these like on fairly steep hills of 10-20% if I can put in 250W of human assistance?

I have a commute of about 40 miles each way. It has two steepish hills quite near my house of approx 200m altitude and a few bumps the rest of the way into London.

At the moment I do this by normally aspirated bike a couple of times a week and car the rest of the time. Come Jan 1 the car will get £14 a day more expensive, doubling the cost, when the congestion charge exemption for EVs dies.

So one option I’m considering is to ride most days using a road ebike (looking at a Bianchi Aria with the X35+ motor at a good price) to take the deep efforts out of it and hopefully be able to manage 4 days a week most of the time.

But if it won’t save me on the big efforts over those hills then I’m probably wasting my money (I currently do them on a 8.5kg bike at about 14-15kph at pretty much max HR / 300-400W)

Oh, and in the UK, these are capped at 16mph/26kph

Have you considered adding a Bafang BBS01 to a bike of your choice. This mid-drive should be a big help on hills. A Tongsheng motor with torque sensors could be more appropriate, but I'm not happy with what I've heard about their reliability. For the next few days a Chinese kit could be priced very well based on my recent experience (IMO, only if they have stock in your country).

If you want the e-assist motor to do all or most of the work climbing, I don't know what to say. I enjoy pedaling uphill. I use the middle level of assist on the steeper grades and try to keep my cadence up around 70, which translates to 4-6 mph. My cadence falls to 50 and speed down under 4 mph on the steepest parts. I could use the maximum level of assist, but I don't do that unless absolutely necessary, like going up my driveway. Even then, I'm only using enough boost to make it up the hill, not see how fast I can get there. However, not everyone feels the way I do about putting in their best effort pedaling. I only call on the motor for more assistance in addition to my effort.

FYI, I have a 1x 10 speed with a 38T front chain ring and an 11-42 cassette. In the rolling hills where I ride I'm shifting a lot and go quickly to my lowest gear on the steeper hills. I need a lower low gear and I'm working on that. I've been behind some people riding their own e-bike on rolling hills. I never saw them use their rear derailleur the whole time I was behind them, while I was shifting up and down my complete gear range. Like I said, people ride differently.

I suspect I would ride more like you. That’s what I meant by 250W of human assistance. I’m not after breaking any speed records, just want to bring down the estimated 2800 calories I used on my last commute to something more sustainable/repeatable day after day. And I would likely use a normal bike some days too.
I just wondered if a hub motor would work well and still contribute at the low speeds of the steepest gradients I have to do. Without emptying the battery too as I think the range of those is close to my total journey. On the flat, which is 60% of the journey, I would be doing all the work as I tend to go ~30kph, that’s one reason I want something close to a non-powered road bike, so I suspect the battery would last ok.

I have an X35+ rear hub motor on a 2020 Orbea Gain. I bought this bike because I have a steep 2km climb home on every ride. I can ride the hill on my conventional bikes, but a couple of the steepest pitches tax me greatly. The rear hub motor (in max assist) makes the steepest bits an aerobic effort with much less muscular fatigue, especially appreciated at the end of a longer ride.

I ride both conventional road bikes and the e-Orbea. Hard to predict range on a charge, 80 miles would be beyond my battery capacity, but not if the motor was in neutral (or off) for long flat sections. I purchased a range extending battery for use in our Cascade Mountains, which is removable for shorter rides.
I know nothing of the Aria - but the EU speed limit will make certain you remain a 'cyclist' who appreciates boosts on hills and/or easier rides in commuter urban traffic. I am on my second battery, now a Mahle branded product.

Donning my speculation hat, a fit rider like yourself on a lightweight, high performance ebike with boost limited to 16mph will easily eke 80 miles from a charge. Other than accelerating from stops and ascending those couple hills you're providing most of the energy.

Could perhaps coax 80 mi from mine with a lot of speed discipline but with a class 3 boost bike capped at 28 mph that's not happening. What I do instead is ride the first 10 or so km on no boost for warmup, switch to low boost for the middle portion then mid boost once the legs start tiring, for the home stretch. Reserve top boost for strong headwind and the like, which steepens battery drain considerably.

If a second, bottle cage battery option is available that can eliminate range anxiety provided you can program it to be used first then charge indoors whilst at work. But I suspect it's not necessary for your scenario.

I have the US spec X35+ (20 MPH max) and wouldn’t rely on it to go 40 miles without a range extender.