Still searching for the holy grail

I thought my latest build (250w cellman kit with 4lb konion cell battery) would be lightweight enough to satisfy me. It's a great bike for going 15mph or so. But it's a slouch on any 'fast' road (tailwind, slight downhill, or anytime you want to go above 18mph). It was easily 5mph slower than my road bike on a slight downhill, coasting on both bikes. That's horrible IMO. I can't be losing that kind of speed (and efficiency). I think it's due to the extra weight (18lbs more than roadie), and therefore higher rolling resistence (running 60psi 1.5in wide 26" tires). I can't run 1" wide tires with that weight. (can I? - not on less than perfect roads).

I love the stealthness of this bike, silent, worry-free drivetrain. But at 36v, it's too slow (17-18mph at best). I think if I go to a 48v batt and infineon controller, this will be an okay bike for commuting purposes. But it will always lack the efficiency that I LOVE about my road bike.

Now I'm thinking of once again thinking of going to an RC drive on a road bike with 700x25 tires. I need to hit this goal - to have an ebike that is nearly as efficient and fast as my road racing bike. I need that speed and efficiency, but with e assist. I want to ride it like a normal road bike without the power on and not feel slow. That's the holy grail, must attain it!

I've gone from currie motors, to geared currie motors, to geared hub motors, and now I think I'm ready to put the money into a superlight RC setup. This will be the sheet if I do it right.

Actually a lot of the secret sauce is in the width of your tires.
On my 700c bike, i went from 38 to 28 tires and it made a huge difference in my pedaling acceleration. Suddenly i could out-pedal the gears, and now i am looking for a larger front crank for that bike.

Weight matters on hills more than it does on a flat.

Try a 1in. tire and you will notice a difference.
You may even gain a mph or two, and your acceleration should be better as well.

But that geared motor won't do much more than 20mph.

veloman said:

. I think it's due to the extra weight (18lbs more than roadie), and therefore higher rolling resistence (running 60psi 1.5in wide 26" tires). I can't run 1" wide tires with that weight. (can I? - not on less than perfect roads)..

Click to expand...

Why not ? .. there are plenty of big guys (250 + lbs ) riding round on those 700c23 road tyres.
but ..there is plenty of evidence to suggest that tyre width is not a factor in rolling resistance. :wink:
.I suspect your problem is elsewhere,...motor drag, bearings , brakes ??

Hillhater said:

Why not ? .. there are plenty of big guys (250 + lbs ) riding round on those 700c23 road tyres.
but ..there is plenty of evidence to suggest that tyre width is not a factor in rolling resistance. :wink:
.I suspect your problem is elsewhere,...motor drag, bearings , brakes ??

Click to expand...

Hm.. i can't disagree more. It depends on how much the tires sag which determines their overall contact patch.

If you have a wide tire at the maximum PSI it can handle, and your weight is not enough to make it flatten, yeah you have equivalently a tire of a narrow width.

If it is not at max psi you will get epic amounts of extra drag. There is a tendency to run tires at lower PSI.

some weeks back, there was a report posted from a bike mag. ( i cannot find the post currently)
It was a review of the latest tire developments from Maxxi (?? i think) where they had done some detailed controlled tests on various tires and shown quite conclusively that some of the wider section tires(1.7 -1.9") had less ROLLING resistance than their top range road race tire !
Note:- wind resistance is obviously a different issue.

I've heard of that test. but please find a link if possible.

Rotating mass in the worst place possible is another. Wider tires generally have more rotating mass.
I can feel the rear 1.95" in tire on my bike dragging me down hard on hills. On flats it helps keep the momentum.

Every small geared hub motor i've ridden on has had a small amount of drag though. Just barely enough to be noticeable.

Hillhater said:

some weeks back, there was a report posted from a bike mag. ( i cannot find the post currently)
It was a review of the latest tire developments from Maxxi (?? i think) where they had done some detailed controlled tests on various tires and shown quite conclusively that some of the wider section tires(1.7 -1.9") had less ROLLING resistance than their top range road race tire !
Note:- wind resistance is obviously a different issue.

Click to expand...

Someone posted this article not long ago:
http://www.bikeradar.com/news/article/bicycle-tires-puncturing-the-myths-29245

Wider tires only have less rolling resistance if all other attributes are equal. I think in most cases the increased weight and lower tire pressure of wider models will generally outweigh any gains from the width in the rolling resistance department.

great article, rifle. Thanks for the link - bookmarked.

Rifle said:

Someone posted this article not long ago:
http://www.bikeradar.com/news/article/bicycle-tires-puncturing-the-myths-29245

Wider tires only have less rolling resistance if all other attributes are equal. I think in most cases the increased weight and lower tire pressure of wider models will generally outweigh any gains from the width in the rolling resistance department.

Click to expand...

Thanks for that.
I guess it depends on what your priorities are .. you could say that the added ride comfort and puncture resistance of the fatter tyre, outweighs any losses in the weight or wind resistance departments ! :wink:
..but the original issue was identifying a significant difference in rolling resistance between them.

Hillhater said:

..but the original issue was identifying a significant difference in rolling resistance between them.

Click to expand...

Maybe you're referring to your own post, but just to be clear, rolling resistance is all I was talking about. The greater weigh increases the rolling resistance as does the lower tire pressure, so the wider tires won't necessarily have a lower rolling resistance unless you can find one that weighs the same and can be inflated to as high a pressure as a skinnier one.

From the article you linked..

... Riders have argued for years that narrower tires – especially on the road – roll faster and are more efficient than wider ones when in fact, the opposite is true. According to Wheel Energy, the key to reducing rolling resistance is minimizing the energy lost to casing deformation, not minimizing how much tread is in contact with the ground. All other factors being equal, wider casings exhibit less 'bulge' as a percentage of their cross-section and also have a shorter section of deflected sidewall.

Click to expand...

since Veloman was looking for a "lost" 5mph, the difference in R Resistance between a 1" and a 1.5" tyre, (at 60psi) would seem unlikely to be the main cause.
However, if he is comparing a 1" slick with a 1.5" knobbly ,... then it maybe so !

Oh and let me touch on RC drive....

More efficient? not from what i've seen O_O
Those motors may run at lower voltage, but are severely amp hungry..

I know what you mean about the efficiency drive and i have given up on it personally.
I let the motor do it's work and forget about it.

I am going to do another build with the cell_man geared hub again. This time i will use the hub motor as a rear chain drive.. with the motor directly above the wheel.

If the geared motor is freewheeling then you only have the drag of the extra freewheel which is quite minimal really.
No rotating mass to drag you down, and you can use regular bike components.

Downside: i will have to bribe a friend into doing some welding for me and the work will involve a spare bike frame for donor dropouts to hold the motor.


Or you can say f*** it and let the motor do the work like i have with the mac motor build, lol

And here I thought rolling resistance depended on co-efficient of friction and weight ... only ...

Cheers,
GT

Just curious, have you put the same extra weight on your road bike and compared it? Like load up with waterbottles and see if you still feel fast?

I have also noticed perceptable drag on gearmotor setups, but using my heavy batteries, I had also made the bike 30 pounds heavier. Damn right it feels sluggish 30 pounds heavier.

I know when I'm carrying a heavy backpack on my roadbike - maybe 20lbs, that I do feel noticeably slower. It could just be the weight. Weight is a weird thing - on paper it shouldn't have that much of an effect when you aren't accelerating or climbing. But I've notice that on most roads, you are either accelerating or decelerating, if only little bits.

Last night I took the ebike home, then immediately got on my 1990 Trek 1400 (a good road bike for it's age, but nothing like the new multi-thousand $ road bikes today). I'm able to go the same speed on the road bike on many sections of road where I would be pulling at least 100-150watts on the ebike, with just coasting. Comparing the two, the only times I actually feel the ebike is benefical is when I'm climbing or going into a serious headwind. It's pathetic how slow the ebike is on any 'fast' section of road (which is a good amount of the time - any downhill or tailwind).

Yes I can just build a 'moped' ebike that will go faster than my road bike and require a big battery and lots of money.

I just HATE feeling so noticeably less efficient on the ebike. I think I might go crazy again trying to find this holy grail. But damn, why can't we add 300watts to a road bike with only 5lbs added, and not require tons of custom fab and huge $? 300watts is PEANUTS, but enough to make a very fast assist road bike.

My roommate's dad just rode the ebike. He thinks I'm on to something...

Once battery cost comes down, I think many more people will jump on the ebike train.


I'm going to start working on a 700c version, should roll faster and get another 1.5mph hopefully. I want to try out ~44-50v... which will mean attempting lipo since I only want 5ah (and the high c rate).

Dude, when you get a faster motor you will stop caring. Trust me on this one.

You don't have to have a moped.. with the right gearing you will be able to contribute plenty of human power to the motor.

You will be able to reach speeds that no human ( other than Lance Armstrong ) can achieve and efficiency won't even be a question, as eBikes are already ridiculously efficient to begin with. Geared motors are about as good as it's gonna get, especially in hilly terrain. The bike is going to be heavy, that's just a fact. I personally cut down the weight by installing higher end components, and using lipos.. Hey, i can still carry the bike up a flight of stairs into my apartment so that's all that matters.

And by pedaling you will reduce the amp load noticeably and increase your top speed.

Man if you were local i'd take you out on a spin on the MAC and there'd be no question in your mind about it

That being said i am going to eventually do another build that runs that MXUS motor as a chain drive on a 700C wheel disc sprocket to eliminate it's drag and rotating mass.
my eZip worked that way and it was actually easier to pedal when the power was off.

When you've only got 200w-ish of human power, everything counts..

Yeah, I understand what you're saying. I'm not at Armstrong's level, but I did race near elite level amateur road events, so I come to expect efficiency and speed. (I could Time Trial at 25mph on 350watts). Just last night I sped ahead of traffic at over 40mph down a hill, stuff like that is soo fun because you know you are at the pinnacle of efficiency on a road bike. (well, for short burst riding. top end speed goes to the streamliners, but they can't accelerate!) I have a powermeter telling me my actual REAL wattage to the rear wheel, and when I'm laying it down in a 2000watt sprint (i.e. 0-30mph in 5 seconds), it's an amazing feeling. Yes, I suppose I do need to let go of the fact that an ebike will always be heavier and less efficient than a road bike. However, there is improvement to be made. A member here did an RC chain drive on his cyclocross bike, I remember watching the video of him ripping around town on it. Lipo is key though, NEED that lightweight high c rate.

I would really like to ride a powerful ebike. All I know are my jerry-rigged low power ebikes, and 250watt geared hub motors.

I think I may do a 30mph 9c build by end of summer. I now work at home, so I have lots of time to tinker. If I can get comfortable with lipo, that would be realistic.

Ah. Low power, low weight, efficient. Geared hub motors have some drag. It's unavoidable because the planetary gears, freewheel, sealed bearings are never going to be as free running as a conventional bicycle wheel. For most of us this isn't a problem because the drag is acceptably low, but if you have a properly fast racing bike and the legs to use it, you will notice it. I think you should look at what Kepler, Adrian_sm are doing in the non-hub forum along with the commercial packaged solution mentioned there. See also http://www.recumbents.com/wisil/tetz/E-AssistMetric/default.htm It looks like it may be possible to build an RC, friction drive setup for under 5Kg total and possibly under 4 and maybe even under 3kg. And when the friction drive is disconnected there's ZERO extra drag. The other thing is to think about when you want assist and how little you can use it. If you only ever use it on steep hills to push your speed from 10mph to 15mph, you can get away with tiny batteries and tiny amounts of assist.

If you can put up with the low drag of a hub motor, I'd look at cellman's kits and making up something like the 350w geared hub. 26" motor in a 700c rim, and an A123 12s1p pack or possibly 12s2p. The small rim motor with a big rim gives you a higher no load rpm at the expense of some hill climb torque. The A123 gives you enough C to run a very small AHr battery. 36v keeps down the total number of cells needed. cellman's BMS makes the battery plug and play. The Infineon controller is well understood and modifiable. And then try and condition yourself not to use it, except when you absolutely need the extra assist.

the kepler setup would probably work amazing for him.

Mind you, it is noisy as hell ( all RC motors are ), and there are mixed reports on that kit.

He already has a cell_man kit and lipo i believe, That's as light as you get for a hub motor until you start looking at crappy low power european motors which are like... 1lb less.... and useless.

veloman said:

Now I'm thinking of once again thinking of going to an RC drive on a road bike with 700x25 tires. I need to hit this goal - to have an ebike that is nearly as efficient and fast as my road racing bike. I need that speed and efficiency, but with e assist. I want to ride it like a normal road bike without the power on and not feel slow. That's the holy grail, must attain it!

Click to expand...

That is the whole reason I bothered with my friction drive design.
Click here for some pics

It definetely ticks the boxes of light weight, no added rolling resistance, feels like a normal road bike, heaps of power (>1000w) if you need it.
It looks stealth, but is not quiet. Just ironing out the final bugs, the major one being good current limiting. But Kepler is very close to having that solved, and ready for release.

I don't know if it is a holy grail, as it won't suit everyone sine you are limited as too how much power you can put through at it, and you notice the sound.
I know I still keep my hub motor, dual suspension bike. But the friction drive sure as hell is a nice compromise.

Adrian