how lightweight do you need your bike to be?

[daveyjones97]

ive had a lot of spare time this week (off sick) and found some interesting stuff.

i dont have much opinion on this and cant vouch for its acuracy but its definately thought provoking if you ride lots of hills and the principle is sound: http://www.smartcycles.com/bike_weight.htm

 

[gogo]

There are a few variables that affect your question. Do you need to be able to lift your bike onto a bus rack or up a flight of stairs?

If you don't have to lift your bike, the energy cost and power requirements due to bike weight can be considered. If you have hills, the weight of the bike + rider will determine how much power is needed. If you do a lot of braking, increased weight will mean proportionally increased energy losses to brake heat.

On the plus side, any energy you use getting mass up a hill is returned going back down.

 

[hjns]

On the plus side, any energy you use getting mass up a hill is returned going back down.

Unfortunately, only a small fraction of that energy is regenerated in your lipos.... and only if you use regen appropriately. If you jump down the hill, most of the energy will be kinetic energy that accumulates during the fall, and you will only feel taht energy when you hit the bottom.....

 

[daveyjones97]

i just put it out there as its interesting, even though everone here is happy with wildly differing rides weight and power concern most of us. im reluctant to say too much as i havent even built my 1st ebike yet! i have spent a good year or so researching the subject as here in the uk we're stuck to 250w which is obviously not enough and having built cars before i fancied my chances of building my own motor, controller and bike. now ive done lots of research i definately dont fancy my chances of making a motor or a controller :lol: still sucking up anything that looks like relevant info though.

 

[hjns]

i just put it out there as its interesting, even though everone here is happy with wildly differing rides weight and power concern most of us. im reluctant to say too much as i havent even built my 1st ebike yet! i have spent a good year or so researching the subject as here in the uk we're stuck to 250w which is obviously not enough and having built cars before i fancied my chances of building my own motor, controller and bike. now ive done lots of research i definately dont fancy my chances of making a motor or a controller :lol: still sucking up anything that looks like relevant info though.

If you are stuck to 250W, build a midmotor setup with gears and have fun!

 

[SamTexas]

I agree with the author. The difference between a 15 and a 17 lbs bike is only of importance to racers.

For ebikes I am even less concerned about weight and more concerned about the cogging effect of the hub motors. It's very frustrating for me to pedal my 9C direct drive hub without battery. But it's almost normal to do the same with the a cell_man economical 350W geared hub.

 

[daveyjones97]

if / when i get round to buying parts i'd like the ability to climb upto 40deg short sharp hills without having to break too much sweat pedalling, 30mph top speed (anymore and i'd probably get careless and get prosecuted) 10 mile range before any drop in power when riding average smaller roads or well used dirt tracks.
i do obey 99.9% of laws, but i would ride my ebike off road half the time and 250w wouldnt cut it on softer power sapping surfces. id like it to be able to maintain 20mph on well sighted dirt tracks and not stall on hills.

 

[Hugues]

if / when i get round to buying parts i'd like the ability to climb upto 40deg short sharp hills without having to break too much sweat pedalling, 30mph top speed (anymore and i'd probably get careless and get prosecuted) 10 mile range before any drop in power when riding average smaller roads or well used dirt tracks.
i do obey 99.9% of laws, but i would ride my ebike off road half the time and 250w wouldnt cut it on softer power sapping surfces. id like it to be able to maintain 20mph on well sighted dirt tracks and not stall on hills.

40 degrees
are we taking about the same thing here ? that's steep.

anyway, for what you describe, you need at least 2'000 w with a direct drive hub. With 250w, you'll go nowhere in the mountains. Just buy a cycle analyst and cap the power to 250 w in the city and open it up to have fun otherwize.

 

[SamTexas]

I don't even know if it's possible to climb a 40% grade incline. 40 degree? Not a chance.

 

[hjns]

I don't even know if it's possible to climb a 40% grade incline. 40 degree? Not a chance.

Hmm. A 45degree slope is a 100%incline. So a 40 degree slope is about 80% ??? I don't have my scientific calculator with me to calculate Tangent of 40 degrees and multiple by 100 to get %.

Looking at the image, it should be possible, with the right underground (no slippery slope) and a 2WD with two slow high torque motors... and it will probably take much more than 2kW.... and your tongue should be touching the front wheel in order to prevent a wheelie .....

 

[SamTexas]

I don't even know if it's possible to climb a 40% grade incline. 40 degree? Not a chance.

Hmm.

Should be possible, with the right underground and a 2WD with two slow high torque motors... and it will probably take much more than 2kW....

Hmm... I still say it's not possible on a normal electric bicycle. The tires will not have the necessary traction. It's not just a matter of torque and power. But I would love to be proven wrong.

 

[daveyjones97]

the 40degree thing would be steps in trails or mini canyons, i cant think of anything ive seen ridden thats more than 50 meters at that steepness, that would be the most extreme example i'd want to ride without having copper dripping out of it and i realise i'd have to pedal and then rest the notor for a few minutes. i like a bit of trials riding, not that im any good at it mind, as well as more general on/off road. ive always been the nutter taking a run at hills and trying to snap the chain on knarly stuff sensible folk just get off and walk! i realise an ebikie that would cruise up 45deg hills would cost 5k min, not last long and wipe every credit card and hard drive within half a mile radius

 

[hjns]

Hmm... I still say it's not possible on a normal electric bicycle. The tires will not have the necessary traction. It's not just a matter of torque and power. But I would love to be proven wrong.

What is your definition of a "normal electric bicycle"???
I am not sure you can point to a single normal ebike here on the ES forum....

 

[MadRhino]

This article has little to do with our E-bikes. We are talking about much more weight, and much more difference in weight, and in power too. Yet, the small numbers can give a good idea of the big ones.

There are different builds here, with a difference in weight over 150 pounds. There are some that run with 250w. and others above 15000w.

Let's say I am in the middle for power, seeing 7000w, but on the low side for weight with a tad above 230 pounds for rider and bike. That is a very powerfull ratio, and I would need much more power to keep the same performance level, if I was to ride at 350 pounds.

Then, there is the weight distribution factor. The difference of power needed to accelerate 10 extra pounds of tire and rim, is higher than if those 10 pounds were on the rider. The weight distribution also affects handling as well as geometry design.

It is not because our bikes are powered, that the weight factor is any less important in the design of our build. It is a major part of the equation, that we have to deal with.


Then, about the 40 degree climbing, I ride the stairs very often, and I believe that many here do it too. If wou want to know if your power to weight ratio is good, try climbing a series of 12 steps from 10 ft start.

 

[SamTexas]

What is your definition of a "normal electric bicycle"???
I am not sure you can point to a single normal ebike here on the ES forum....

I would say that 99.9% of the ebikes here are normal. My point was that you need extra special studded tires to provide sufficient traction to get up a 40 degree incline, if at all possible. Most likely, the bicycle would flip backward at the slightest power/torque application to the rear wheel on that incline.

 

[SamTexas]

Then, about the 40 degree climbing, I ride the stairs very often, and I believe that many here do it too. If wou want to know if your power to weight ratio is good, try climbing a series of 12 steps from 10 ft start.

I would love to see a video of someone climbing a 40 degree stairs.

 

[daveyjones97]

what madrhino says about stair climbing (when no-ones around...) is very much the sort of short sharp shock 15-30seconds max of loading i would like to make a bike cope with. im after torque rather than speed as im in the uk and as i found when i had silly cars; if i have the power, i use it, get careless and get caught im talking a shock loading like that 1 or 2 times a month and im cool with pedalling for extreme climbs.
my problem is theres so many different ways of doing an ebike that the more i read the harder its getting to nail down a parts/spec wish list

 

[daveyjones97]

youtube will show you there are skilled folk (not me) who can pedal a mtb up 45degree slopes without a run, and much steeper with a run. i have ridden up stuff close to that myself but im not talking about making a ebike do that on a regular basis as it would be for roads and mild trail riding most of the time

 

[Pure]

Weight is of little issue for even a moderately powered e-bike on flat ground. My bike @ a lil over 1900Ws has the same top speed with my 250# ass as it does with my buddy's 180#. It may accelerate a little better for him, but not enough to really notice. Now hills may be a different story, but since Florida is flat I can't compare. But with that said, what little bit of weight that can be saved with the use of "lightweight" parts, won't make a bit of a difference for just about any e-bike. Now peddle only bikes are a different story.

 

[Hugues]

....without having copper dripping out of it ....

on a paved and dry road i might be able to climb 20-25 % grade, but on nasty trails with rocks, muds, grass, 20% is pretty much the limit, with my gear )see sig below)

 

[MadRhino]

I would love to see a video of someone climbing a 40 degree stairs.

Well, I shall make one, but just for fun...

Here's Charlie trying my Demo 8 on the first day of its build. This was with limited power, and the stairs at the end were not 40 degrees, but he took them very slowly on the 11t gear. Yet, the bike is not the same now, and it sure laugh at stairs that are much longer and steeper.

[youtube]7FbKBMhk6pQ[/youtube]

 

[SamTexas]

Well, I shall make one, but just for fun...

Thanks. I look forward to seeing it.

Here's Charlie trying my Demo 8 on the first day of its build. This was with limited power, and the stairs at the end were not 40 degrees, but he took them very slowly on the 11t gear. Yet, the bike is not the same now, and it sure laugh at stairs that are much longer and steeper.

How steep do you think those stairs are? More or less than 30%?

That's a very functional and powerful bike.

 

[daveyjones97]

dont mean to stir a hornets nest but stair climbing is comfortably in the capabilities of a gas trials bike with a skilled rider, guess those bikes are 10+ hp or 7500w minimum though and pretty light

 

[SamTexas]

Yep. You guys are right. Looks like 40 degree is doable. I stand corrected.

http://www.youtube.com/watch?v=kqLXQ8vBVKs

 

[MadRhino]

How steep do you think those stairs are? More or less than 30%?

I believe those stairs are about 33 degrees.

That's a very functional and powerful bike.

Thanks. Like I said, the bike is not the same now. This was only an experimental first ride and Charlie was riding it so I could see its handling and know what to improve. The build is much better completed and fine tuned 6 month later, and now has more than twice the power that you see in that vid.