Lightweight folder - build thread

*** Title edited - this will now be the build thread ***

Some background. I use my full sus folder ebike more than any other, it lives in the back of the car and gets used a lot, mainly for fairly short trips around the local city, never more than around 10 miles, mostly trips of maybe 4 or 5 miles. It's great, but despite having an alloy frame it isn't as light as it could be, due to the full suspension, gears that I don't need and a larger than needed battery pack. This makes heaving it in and out of the car a bit of a nuisance.

For some time I've been toying with the idea of building a really light, short range, folding ebike, probably still using a Bafang/8 Fun hub to get a decent bit of performance, but with no gears and no suspension. 20" wheels are a must, anything smaller is going to give a rougher ride than I'd like and make getting a fast enough motor and crank gearing difficult. Ideally I'd like to just buy a bare frame, preferable alloy so I don't have to worry about rust from dings, and then fit just the parts I need. I'll go with a small battery pack, maybe just 5Ah of LiCoO2 LiPo at 10 or 12 S. I'll build up a custom 6 FET controller for it, like the one I have on the existing folder. The idea is to get the weight down from the ~19 kg (~42 lbs) of the existing bike to maybe 12 kg at most if I can do it.

Anyone got any suggestions as to a good, lightweight, but not too expensive, frame choice, ideally in Europe, rather than further away?

Not European, but I've often thought that theXootr Swift would make a great ebike, and it's the only one I know that of that sells the frameset on its own.

The Swift frame is constructed of 6061-T6 custom-profiled aluminum tubing, TIG welded. The patent-pending TrusFold system provides maximum frame rigidity. The frame set includes the frame (obviously), fork (CroMoly straight taper) and headset, riser with quick release lever, seat post with two quick-release levers, and rear derailleur hanger.

We have had a number of folks ask us how much the frame weighs. The frame with the headset and fork weighs 7lbs, 13.5oz (approx. 3.6 kgs). The seat post, riser, derailer hanger, and QR levers are 2lbs, 10.8oz (approx. 1.2 kgs). These weights were taking with our packing scale so they are not 100% precise, but they are very close.

Click to expand...

JennyB said:

Not European, but I've often thought that theXootr Swift would make a great ebike, and it's the only one I know that of that sells the frameset on its own.

Click to expand...

You used to be able get the Airnimal Rhino frameset - not sure if it's still available or not. It has suspension and is not exactly budget, though:


http://www.airnimal.eu/Rhino/

Thanks folks, particularly that link to the Xootr folder, Jenny, the single speed version looks to be just what I'm after, plus it has the advantage of using pretty standard bike parts by the look of it. I like the way it has horizontal rear drop outs as standard, too, makes fitting a single speed easy.

I'm afraid the Airnimal, nice as it is, is outside the budget!

I've contacted Xootr to see how much it would cost to ship a frameset over here. Hopefully it won't be so expensive as to rule it out.

Thanks again,

Jeremy

It's still pretty new (as in - "lacks the robustness proof over time"), but my MENSTRUAL cycle project has proven to be well balanced, light weight and full of pep. The basic premise is RC drive to the left side using an Astro 3210 and a Recumpense V4 drive (5:1 belt reduction).

There are definitely less expensive ways to do RC, and I don't have any precise figures on the weight of the drive system. But beyond the subjectively light weight and even balance, I like that have a great range of e-power without sacrificing any pedal-only gearing.

I have to agree that 20" (406mm wheels) are a great size for a folding bike. One really doesn't gain much compactness by going to a 16" tire size, but components get harder to source and pothole performance suffers.

Have you tried the brompton? I've been looking a long time for a lightweight folder and nothing beat the brompton.

I also thought that a 16" wheel wouldn't be nice to ride, and actually I'm quite happy with it. Furthermore, it's an steel frame so you can easily apply more speed to it. I run at 30 mph with it.

It's not heavier than a standard aluminium frame bike, around 11-12 kg the bike.

You can buy it around 400£ second hand in gumtree, without too much problem. If needed, I can help you get one from gumtree in london. The only issue is that a lot of them are stolen.

Another alternative is the Dahon speed uno:

http://www.dahon.com/bikes/2011/mu-uno

It's weight 10 kg and is also quite cheap (around £400 and less if you get it second hand). It folds quite cleanly but part are difficult to find as Dahon brand do custom parts.

Funny you should mention the Brompton, as that's what triggered this idea again this morning. I was stopped by a chap while riding back to the car park from town, who was interested in my bike. He owned a Brompton (and the lady he was with was a Birdie fan). I mentioned to him that I'd like the bike to be a bit lighter, and he picked my bike up and reckoned the Brompton he had (steel framed) wasn't a lot lighter. On the drive home I got thinking about resurrecting the lightweight folder again, hence this thread.

I did take a look at a Dahon Mu P8, a while but wasn't that taken with the design, TBH, and wasn't wholly convinced that it wuld be much better than the cheap alloy folder I have at the moment.

As an aside, I am getting used to being stopped and asked about the bike in town, but today was unusual, as I had three people stop me, chat at length about the bike, and two asked if I could build ebikes for them. Must be the warm weather...........

A bit more pricey but the roll-around-after-folded feature is pretty cool - IF Reach Folding Bike.

Budget priced: Downtube Nova - many hi-Res photos. Youtube of Nova w/Mac.

Buyer's Guide for Folders.

I owned the Pacific if reach few months ago. It was really nice to peddal but the rear dropout is only at 120 mm and if you have a motor you'll have to customise the axle in order to accept the folding magnet (it allows the bike to remain folded).


But I sold it because it wasn't compact enough for multi-modal commuting. I brought it once to restaurant and didn't find anywhere to park the bike (inside the restaurant), we had to hide it inside the toilet :lol: . Since then, I purchased a brompton and can leave it inside restaurant next to my table once folded because it doesn't take much space.

If you go to shop, stairs, bus and restaurant, there isn't any bike more practical than the brompton. That's why I'm on the brompton only now :lol:

Check the brompton configurator:
http://www.nycewheels.com/brompton-folding-bike-alc-custom-video-configurator.html

If you get a single speed brompton and other lightweight options, even a steel brompton can weight around 10kg. I can't see many bike that are nice to ride of that weight.

Thanks for all the advice, much appreciated.

Matty, the most useful thing from your build for me was the cheaper alternative to the expensive Schlumpf drive. I've struggled to get a decent ratio on my current folder, as big chain wheels are a pain (the 50T I have is about as big as I can go without risking damage with ground contact when the bike's folded), and getting hold of small rear freewheels isn't easy, either. The idea of being able to have a small chainring and standard rear sprocket, yet still get the equivalent of something like a 72 or 78 T chainring sounds great - I should be able to pedal at close to top speed. I'm going to order one of the ATS Speed Drives from Accountant.

I do quite like the Brompton, but the non-standard parts and small wheels make it less than ideal. I'm waiting to here how much it will cost to ship one of the Swift framesets over here, if it's not mega expensive then that's probably the way I'll go. Interestingly, the Swift folds in a fairly similar way to the Brompton, but has the big advantage of using standard bike parts. With the frame, forks, headset, riser and seat post weighing in at just4.8 kg it isn't too heavy, either.

I've ordered a new Bafang motor, plus some rims and spokes, so as soon as I decide on the frame I should be set to go. No doubt it'll be all the little stuff that pushes the price up on this build - that's what usually seems to happen.................

Jeremy Harris said:

Matty, the most useful thing from your build for me was the cheaper alternative to the expensive Schlumpf drive.

Click to expand...

Happy to be of service!
You've no doubt seen the trouble I had getting the bottom bracket machined to the 45* chamfer. A machine chop can do it, but I held out for the real-deal Schlumpf tool. Also if your BB width is 68mm even, you might want to have spacers in hand. The waiting was torture! Other than that the ATS drive/Schlumpf drive was easy to install, and well worth it!

This is another budget alternative to the Schlumpf:
http://pattersonbike.com/

Luckily the spacers aren't hard to make.

Note that Schlumpf makes special models for some bikes, the ATS version may not fit everything.

On the Borg I run mine in speed mode all the time, nice to have a large effective chainring.

Miles said:

This is another budget alternative to the Schlumpf:
http://pattersonbike.com/

Click to expand...

I did take a look at that one earlier, but the downside is that it comes with a fixed chainring that's too small for a 20" wheel bike. The largest effective chainring size with the Patterson is only 45T, unfortunately.

Alan B said:

Luckily the spacers aren't hard to make.

Note that Schlumpf makes special models for some bikes, the ATS version may not fit everything.

On the Borg I run mine in speed mode all the time, nice to have a large effective chainring.

Click to expand...

I noted the point about spacers - seems odd that it doesn't fit a 68mm BB as standard, as there are a heck of a lot of bikes around with that width BB. I reckon I can machine the BB OK without the special tool, as long as I take some time to make up a proper jig to hold the frame in the milling machine accurately.

I've never changed out of the highest gear on my current folder, so having the gears is just carrying around ballast. Unfortunately I've only been able to get a 12T sprocket, and with the 50T chainring it's not really comfortable pedalling at 20 mph plus.

I think there is a lot of variation in the 68mm "standard" bottom brackets, and the Schlumpf is more sensitive to these due to the method of attachment. They supply a 0mm spacer, and they have 2,4,6mm spacers in steel and aluminum. They indicate using the opposite material as the frame for best "grip". In my case the 6mm spacer was not in stock and I was impatient, so I made one on the lathe in a couple of hours (probably less than half that time for a machinist to do it, or a few minutes for CNC). Then the bike mechanic tells me, maybe 7mm would have been better. But I went with the 6 and it has been working fine.

Jeremy Harris said:

I noted the point about spacers - seems odd that it doesn't fit a 68mm BB as standard, as there are a heck of a lot of bikes around with that width BB

Click to expand...

Ilia makes the point in his installation video (at bikessf.com) not to take too much BB cup material off. I think that's the kicker. How much is too much? Lacking experience, decided "too much" meant enough to make the lip of the BB too thin, and I has some nice beefy BB cups. That's probably true also, but as I found out the hard way "too much" also means "such that your BB width is too narrow for proper torque"

I was probably only a few tenths of a mm too narrow.

You are right of course, Schlumpf and ATS could easily throw on a few more turns of thread so that people like me are covered... but they don't. So bottom line, knowing the consequence of too much chamfering is the need for spacers, you'll be equipped to take measurements, take off less metal, and likely not need spacers.

My experience was complicated. First I went to Ilia, and he cut the chamfer, then he found that we needed wider washers, the threads bottomed out without it grasping the shell. Ilia did not have the washers, apparently they are not needed in most installs. Then I took it to Cyclemonkey/East Bay Bicycle Workshop and Stefan did the final install. He had a technique for measuring the amount of chamfer, and he cut a bit more than Ilia had already. If too little chamfer is cut the surface area is reduced and the drive can slip. When the measurement was correct he tried the spacers he had on hand and it would not tighten up with the 4mm spacer, so he loaned me the 4mm spacer and I made the 6mm spacer from 6061-T6 aluminum bar stock, about 2" in diameter, making a lot of swarf for this thin little washer. Photos in my Borg thread and album.

So there is a way of measuring with a caliper the proper amount of chamfer. I don't recall the value, but it may be somewhere in the Schlumpf installation instructions. Or perhaps Stefan knows it some other way. I think he was measuring the OD of the chamfer since it grows from the ID outward as it is cut. The shop there has done a lot of these installs. The fellow I talked to first at Cyclemonkey indicated that most installs did not need more than 2 or 4mm, so 6mm is apparently unusual. They had 6mm spacers on order but were uncertain when they would arrive. As it turned out they probably arrived the day I came back for the final install but we used the one I made.

View attachment 1
I love my downtube folder and you can still get them for about $400 from the downtube website. Full suspension is above.

My Downtube is a hard tail with a bmc front wheel drive and Ilia installed a schlumpf on it and it makes a hug difference on ride quality. Its great being able to pedal assist at 30mph. Unfortunately price of sclumpf has gone up a lot since a few years ago when i bought mine.

Alan B said:

My experience was complicated. First I went to Ilia, and he cut the chamfer, then he found that we needed wider washers, the threads bottomed out without it grasping the shell. Ilia did not have the washers, apparently they are not needed in most installs. Then I took it to Cyclemonkey/East Bay Bicycle Workshop and Stefan did the final install. He had a technique for measuring the amount of chamfer, and he cut a bit more than Ilia had already. If too little chamfer is cut the surface area is reduced and the drive can slip. When the measurement was correct he tried the spacers he had on hand and it would not tighten up with the 4mm spacer, so he loaned me the 4mm spacer and I made the 6mm spacer from 6061-T6 aluminum bar stock, about 2" in diameter, making a lot of swarf for this thin little washer. Photos in my Borg thread and album.

So there is a way of measuring with a caliper the proper amount of chamfer. I don't recall the value, but it may be somewhere in the Schlumpf installation instructions. Or perhaps Stefan knows it some other way. I think he was measuring the OD of the chamfer since it grows from the ID outward as it is cut. The shop there has done a lot of these installs. The fellow I talked to first at Cyclemonkey indicated that most installs did not need more than 2 or 4mm, so 6mm is apparently unusual. They had 6mm spacers on order but were uncertain when they would arrive. As it turned out they probably arrived the day I came back for the final install but we used the one I made.

Click to expand...

Thanks, that's useful to know.

I think it should be possible to carefully measure the drive in the fully tightened position, then measure the BB, and work back to determine how much needs to be taken out when cutting the chamfers to get a good tight fit. With a bit of luck I may be able to get away without needing to use spacers.

Green Machine said:

View attachment 1
I love my downtube folder and you can still get them for about $400 from the downtube website. Full suspension is above.

My Downtube is a hard tail with a bmc front wheel drive and Ilia installed a schlumpf on it and it makes a hug difference on ride quality. Its great being able to pedal assist at 30mph. Unfortunately price of sclumpf has gone up a lot since a few years ago when i bought mine.

Click to expand...

I tried to buy a Downtube a couple of years ago, but they weren't able to sell them over here then. Pity, as I like the design - the straight top tube makes for a cleaner look than many folders, in my view. It's probably one reason that I like the look of the Swift.

I suspect it is even simpler than that, Jeremy. Measure the OD of the washer. That's the only thing that contacts the chamfer. That way the whole surface of the washer is contacting the chamfer. Anyway, I'm sure you can work it out.

Good luck with your search. I want a good folder, too, so this is a useful thread. Thanks!

Bromptons feel like (from experience) what it might feel like riding a handicapped grocery scooter. Haha just kidding. The kick shift two speed drive on it was nice.. But not what u need I guess.

What do y'all think about this?

http://www.khsbicycles.com/10_mocha_06.htm


I particularly like the rear rack but have no experience evaluating a folder. 'been lurking on this thread...

Nice looking frame design, I like the built in rack, it makes the bike look better balanced, visually. Spec looks reasonable, but for a folder it's slightly on the heavy side at 32 lbs (14.5 kg) I think. Price looks good though, and there's potential for saving a tiny bit of weight by changing the steel seat post and handlebar riser to alloy. The 40T chainring is way too small, even with the 11/28 block. Top speed when pedalling like mad would be somewhere around 15 mph, I think. Easy enough to swap out the crankset for one with a bigger chainring, though.

Might make a nice basis for an ebike with that built in rack, handy for mounting the battery pack and controller. If it were me then I'd bin the gears, fit a high speed drive crankset, fit a geared high speed wind hub motor and single sprocket and make up a small battery pack to fit the rack.

I've been thinking about making the wiring, battery and controller installation neater for this new build. Connectors are the problem really, as no matter what I do they always seem to clutter things up. I'm planning on fitting the controller and battery pack in a slim alloy case that fits to a rack and making a multi-pole high current connector that also acts as part of the mounting for the case. I reckon I should be able to fit a row of 4mm RC type connectors into a plastic block, with their mating halves in another plastic block, so that I can just unlatch the controller/battery case and disconnect it from the bike for charging, or even just to make the bike lighter when lifting it in and out of the car. The connector block would need at least 11 pins; 3 phase wires, 3 hall wires, +5V, 0V, throttle signal, my simple "fuel guage" signal, and a power on/off signal from a handlebar switch. I'll probably build-in an RFID switch to the case, like my current folder. I have a bunch of 4mm connectors so might experiment and see what I can come up with.