What advantage to having a lightweight Ebike?

[JerseyJoe]

I've seen a few carbon fibre Bosch bikes recently and one really blew me away, I reckon it was about 25-26lbs. It was tricked out with every lightweight gizmo you could imagine. About the weight of my first road bike! Is there any positive advantage in battery life/speed/reliability/hill climbing?

[Jezrant]

The advantage is that it feels more like riding a conventional road bike. This may appeal to people who are keen cyclists but for whatever reason now need a little help on hills. I like the idea. I presume you’re referring to the new Bosch SX motor? Specialized beat them to it with the Creo 2. Doubt many are sold in the UK though. Way too pricey.

[Cugel]

I've seen a few carbon fibre Bosch bikes recently and one really blew me away, I reckon it was about 25-26lbs. It was tricked out with every lightweight gizmo you could imagine. About the weight of my first road bike! Is there any positive advantage in battery life/speed/reliability/hill climbing?

What kind of bike (for which purposes) are you wanting? You can certainly find numerous road or gravel-style bikes with an electric motor that weigh in total as little as 11 kg; or ten times as many e-bikes that weight no more than 16 kg.

In truth, the extra weight of an e-bike is less important than the configuration of the bike for a purpose. Even an 18 kg e-bike built as a road bike can perform surprisingly well compared to a non-motored bike of similar design when not being powered by the motor.

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In our house we like to do road riding and some gravel riding on the less demanding forest roads (built for logging lorries so quite well-made). Me and the ladywife have three Fazua road bikes we ride between us.

One is an out & out racer bike style; another is what's generally called an endurance style and a third is more of a touring bike style. Weights are 13.5 kg, 16 kg and 14.5 kg respectively with their motors and batteries in. All can be ridden without the motor/battery unit mounted (an empty downtube container goes into the frame instead, for waterproof and cake carrying) which knocks 3 kg of those bike weights.

The ride feel is near-identical to any of the bike types that don't have a motor. One advantage, though, is that the centre of gravity is lowered and brought forward a little via the motor/battery in the down tube. This provides a very planted feel, especially on fast and bendy descents.

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For some good insights into why bike weight matters far less than the advertising of lightweight parts would have us believe, have a read of this article:

https://www.cyclingabout.com/why-we-sho ... ar-weight/

The conclusion of the experiments described come to this:

"The data is quite clear; bike weight is not as important as you think! My real-world testing, along with the numbers from the mathematical models, suggests that a kilogram extra weight will likely add one or two minutes on a hilly 100km bike ride. And on a flat route, a kilogram is likely worth 10 or 20 seconds over 100km."

[Cugel]

Is there any positive advantage in battery life/speed/reliability/hill climbing?

In answer to your second question ......

Fundamentally, you can treat a lightweight road bike with a motor as an ordinary bike with the added ability to give your legs the feel of a much fitter rider when that is needed by the terrain ridden over. As the speed with motor assistance is limited to 15.5mph before the motor automatically cuts out, you tend to use the "magically stronger legs" motor assistance when climbing or battling against a strong headwind - i.e. when you speed on an unpowered bike would be reduce to low single figures or you'd have to get off and walk.

On the flat and downhill, you'll likely be going above 15.5mph and not be in need of the motor. Having the motor able to propel you faster on the flat, say, might be nice but for most cyclists its not really essential to go a lot faster than 15/16 mph- although you still can with your leg power alone if you're reasonably fit.

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Personally I use the motor only on the steeper and longer hills of a ride. The battery has 250 watt-hrs and this will usually last me around 150 - 180 kilometers of riding (via, say, 3 or 4 rides) before I need to recharge the battery. This is achieved by using only the necessary amount of power to keep going up the hills at a pace more than a 3.5 mph crawl! Most of the time, I ride with the motor off.

Most e-bike systems have software enabling you to set assistance level profiles to suit your needs and wants. The Fazua system on the e-bikes we ride in our house are typically set to give gradual power assistance that increases with the pedal power put in by the rider. For example:

Level 1: 0 to 75 watts motor power added gradually as the rider inputs pedal power from 75 watts to 150 watts.

Level 2: 0 to 140 watts motor power added gradually as the rider inputs pedal power from 90 watts to 180 watts.

Level 3 (not yet used - got the bonk mode): 0 - 220 watts motor power added as the rider inputs pedal power from 50 watts to 100 watts

[Audax67]

The main advantage I can see is not putting your back out or giving yourself a hernia when putting it in the car or onto the workstand. And not breaking something pricey when you clamp it in and let it dangle by the seat post.

And of course it's easier on the hills when you get bloody-minded and turn the motor off. Did that yesterday: legs still sore but it was worth it.

[Jezrant]

In the Cyclingabout article mentioned above, which is primarily about loaded touring, the author actually lists a few cases where shedding weight on the bike does matter more than you think:

2. To improve bike handling and feel.
Heavy bikes don’t feel as snappy or responsive when accelerating or cornering, making them feel a little less inspiring to ride.

I haven't tried one yet, but I'd expect the latest lightweight carbon fibre road & gravel e-bikes that the OP is referring to handle and feel better than the ones with the bigger and heavier motors and batteries that also require less rider input.

[Cugel]

In the Cyclingabout article mentioned above, which is primarily about loaded touring, the author actually lists a few cases where shedding weight on the bike does matter more than you think:

2. To improve bike handling and feel.
Heavy bikes don’t feel as snappy or responsive when accelerating or cornering, making them feel a little less inspiring to ride.

I haven't tried one yet, but I'd expect the latest lightweight carbon fibre road & gravel e-bikes that the OP is referring to handle and feel better than the ones with the bigger and heavier motors and batteries that also require less rider input.

It isn't always easy to understand fully what aspects of a particular bike make it "snappy" or more responsive. Whilst its true that bike weight affects the rate of acceleration of the bike for a given power input (from rider or motor) there are many other factors that contribute. The steering geometry; the weight and compliance of the tyres; the ability (or lack of it) of the frame to return flex-energy to forward motion; the aerodynamic drag factor of the bike + rider configuration; and so forth.

There are racing style e-bikes that weight near 20 kg yet they're claimed to still feel like a racing bike, even if acceleration is somewhat affected. After all, a bike weight increase from 15 - 20 kg is of itself no different than one rider weighing 5 kg more than another.

In short, bike design and configuration generally has more influence on any "snappy" feeling or lack of it than just bike weight.

[TheBomber]

The main advantage I can see is not putting your back out or giving yourself a hernia when putting it in the car or onto the workstand.

In a similar vain, if you take the bike on a train you may well have to carry it over bridges. My wife has certainly appreciated the low weight of hers while holidaying in France for that reason.

[pjclinch]

Go to a MTB trail centre these days and it seems like acoustic bikes are getting to be in the minority. Obviously an e-bike makes getting up to the top a lot easier, but for mountain biking extra weight also makes coming down harder work. Gravity gives you all the energy you need but controlling the bike takes work, and controlling a heavier bike takes more work. So it's genuinely useful for an e-MTB to be as light as reasonably possible.

Pete.

[Cowsham]

The main advantage I can see is not putting your back out or giving yourself a hernia when putting it in the car or onto the workstand.

In a similar vain, if you take the bike on a train you may well have to carry it over bridges. My wife has certainly appreciated the low weight of hers while holidaying in France for that reason.

Found that last year -- advantages -- faster than taking the bus but lifting it over stiles up steps over gates was a bit of a pain hence I'm taking my non electric bike this time on my annual trip to the island.

[Audax67]

One drawback with many 'sporty' electric bikes is that they have low bottom brackets, so that you have to stop pedalling in tight curves to avoid pedal strikes; and when you stop pedalling the motor cuts out.

[Cugel]

One drawback with many 'sporty' electric bikes is that they have low bottom brackets, so that you have to stop pedalling in tight curves to avoid pedal strikes; and when you stop pedalling the motor cuts out.

Is that so? Do you have a list or some examples? I've not noticed a lower BB on any of our Fazua bikes but that's not to say they might not be compared to the same model without a motor.

Why would the designers lower the BB of such bikes, I wonder?

Cugel

[rareposter]

Why would the designers lower the BB of such bikes, I wonder?

They don't - BB drop (vertical distance between centre of BB and centre of front and rear wheel axles) and BB height (distance between centre of BB and the ground) are a product of all sorts of characteristics of the bike. Drop is static on any given bike unless you have "flip-chips" - little adjusters that can alter head angle and BB drop by a degree or a few mm respectively.

Height can be changed by a few mm either way through altering tyres and forks.

BB height is set far more by what the designer is aiming to get from the bike and that's always going to involve compromises either way.

That said, lower CofG on a heavy bike is a definite plus point, you want that battery and motor weight as low and central as possible otherwise it really starts to affect the handling. Therefore with a lighter e-bike, you can run the BB a fraction higher for increased clearance without the weight getting out of hand.