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Folding Bike design & build

A slim folded bike

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Alan Jackson09/04/2019 17:21:43
197 forum posts
82 photos

I know this is not Model Engineering but it certainly kept me occupied in my workshop so I hope it is not too off topic a subject here. For years I have been trying to design and build a folding bike that can be folded easily into a slim and manageable folded package and have now patented the idea. The idea was to try to get to a small slim suitcase arrangement that can be carried close to the body or wheeled on the front wheel when folded, using the seatpost extended, in a similar way as a suitcase is wheeled at airports etc. Most folding bikes fold in the centre of the frame on a vertical hinge that brings the wheels side by side. Then the handlebars are folded alongside the folded assembly. This results in a smaller side view envelope but a much wider end view envelope due to the wheel widths, pedals and handlebars. Making generally a wide package of about 350 to 400mm.This is difficult to carry because it must be held away from the body, giving the upper arm muscle a severe work out. In the folded position they are usually wheeled on additional small castor wheels, which are only suitable for smooth surfaces. So over any uneven terrain they must be carried. The width also limits loading more than one bike in many vehicles.

This bike uses the frame components to actuate the folding mechanics, avoiding, tough to operate, overcentre clamps etc. There are only two hand operated clamps, one at the rear stay and one for front wheel. The seatpost actuates a strong locking method and the seat tube is unlocked when the rear stay is folded. The handlebars are automatically unlocked when they are set in the folded position. When folded, the seat post can be withdrawn freely up to a limiting stop, and used as an extended handle, as with a suitcase. The brake cables are hidden inside the handlebars to give a clean uncluttered look. The folded handlebars lock under the rear wheel rim enabling the package to be carried, using the steering tube as a lifting handle. The pedals can be folded inside the package, the lower pedal acts as a stand for the folded bike. The low frame enables easy mounting avoiding the rider having to cock their leg over the saddle. The folded dimensions are 720mm long, 520mm high, and 160mm wide, with 16inch wheels. The bike weighs 10kg (22lbs) but this could be reduced with better materials. The frame components are only mild steel rectangular box section, so there is much scope here.

There are some more pics in my album




top view folded.jpg

Edited By Alan Jackson on 09/04/2019 17:22:29

Mike Poole09/04/2019 17:43:13
2620 forum posts
63 photos

Looks well thought out and engineered Alan, must have burnt some midnight oil on designing that. Nice job.


Rik Shaw09/04/2019 17:43:54
1344 forum posts
364 photos

Lovely piece of design Allan - well done. What does it weigh?


Paul Kemp09/04/2019 18:06:37
515 forum posts
18 photos

He says it weighs 10kg?

Nice job.


blowlamp09/04/2019 18:42:49
1376 forum posts
85 photos

Call it the 'Jackson 5x2'.

Roderick Jenkins09/04/2019 19:52:32
1898 forum posts
489 photos

That's very neat. As a folding bike owner I appreciate many of the issues you have overcome. What is the transmission system/ratios?



the artfull-codger09/04/2019 20:43:24
254 forum posts

Well done Alan nice looking cycle, looks like we've got another Dr David Hon in our mists, he spent 7 yrs developing a folding bicycle in his garage & took his design to leading manufacturers who wern't interested, so with his brother he started his own company,[dahon] they are now the largest folding bike manufacturers in the world, I have a dahon cadenza, it has 8 hub gear speeds [none of the exposed derailleur gears & sprockets to gather dirt & salt,] a stainless steel chain disk brakes & full size wheels, a beautifull bike.


V8Eng09/04/2019 21:14:21
1449 forum posts
28 photos

Well done Alan that is a nice bit of design and really good professional looking finished product.

Edited By V8Eng on 09/04/2019 21:28:46

John Olsen10/04/2019 01:15:49
1049 forum posts
91 photos
1 articles

My wife and I took a couple of Dahon folding bikes on a world tour last year, which meant they had to fit into a standard airline check in bag size. That means 1580mm max total dimensions of the bag, and under 23 kg. So small bikes are of interest, since the trip was successful enough that we would love to do the same sort of thing again. This looks like a promising design, but I would echo the question someone asked above, what is the gearing like. It is hard to get a high enough top gear with small wheels. Not that you are going to want to go extremely Dahon has the 16 inch wheels and an 8 speed derailleur. The bottom gear is plenty low enough, the top could be a little higher but it is really hard to do that since you need a larger front sprocket. It has been done but they are hard to get, I might have to make one. The gear hub inside the back wheel is a good idea, again provided you can manage to source something suitable.

The other thing I would suggest thinking about is a carrier of some sort. My wife's Dahon came with one and it does not significantly affect the folded size. I had to buy and fit one for mine, which meant a bit of modification on the milling machine, but again it can be left on when folded and still fit the airline bag. I did fit it using quick release fasteners so that it can be taken off easily. Even if you do not plan airline travel, one of the good uses for a folding bike is trips to the shops from either a small apartment or even a caravan or campervan. (US RV) You may not need (or want!) to carry a lot of stuff but it is a handy thing to be able to do. We were able to fold down the big bag once the bike was out and strap it on the little carrier, wear the carry on, and bicycle to our bed and breakfast places.

The Dahons are around the 11 or 12 kg mark, which leaves a bit of extra available in the bag to carry clothes etc. Between that and our carry on bags, we were able to travel for two months quite comfortably. Of course there are little expedients to keep the weight of the bags down, like wearing the camera and keeping the lenses in my pockets.

Bikes are a bit frustrating, when you think that the 12 kg or so of mostly aluminium should be able to pack down into under 30 litres or so, if only there was a simple way to do that. Well, we could pack it down OK by melting it, but getting it unpacked would be more of a challenge.


Bill Phinn10/04/2019 01:57:25
335 forum posts
67 photos

Very interested to see this, Alan. It looks very appealing.

I'd echo Roderick in liking to know what gearing it has.

Other questions:

  • Is there any adjustment on the handlebars, whether up and down or towards/away from the rider? If not, how practicable would this be to incorporate into the design?
  • Is there a tool-free wheel release system?
  • Would it be possible to fit clipless MTB-style pedals and still be able to fold them in?
Alan Jackson10/04/2019 11:36:04
197 forum posts
82 photos

Thank you for your kind comments and as to the Dahon reference, I too have shown this to some manufacturers who have shown a similar response. They liked it, but also said it would cost a lot to develop etc. They were generally too risk averse and conventional. Most folding bikes are just a reassembly of many standard parts on a hinged frame. On this bike I disregarded convention (Threw caution to the wind, as they say) but convention and caution rule. The gear ratio is about 50 gear inches, which suits a midrange ratio for general purposes. The hard part of any design is to set the design requirements. The phrase you can only have any two of the following, springs to mind: Time, Quality, Cost.

On this bike I wanted about a three to one gear ration for the small wheels. Using a conventional chain of 0.500” pitch will give a large minimum 48 tooth chainwheel. I chose an 8mm pitch chain which reduces the chainwheel size massively. I calculated that with a slightly reduced pedal crank length (Which even expert cyclists failed to notice) driving a smaller wheel diameter it would take a 400lb person, standing on one pedal, (mustn’t just say man) to break the chain. And if that was not enough safety factor, then a duplex 8mm chain could be used with minimal width increase, which, would have the same strength as a 0.500” chain. However, this seemed too big a risk for very conventional, cautious minds. The Chain runs in angle section frame members, thus using the frame as a chain guard. As to handlebar adjustment the bike is designed around an average sized adult.

The handlebars are fixed in position, but the saddle can be easily adjusted. There has to be compromises or it will only fold up badly. Look at a Brompton, the horizontal distance between the saddle and handlebars is controlled by having to accommodate the rear wheel in the folded position. My biased view is that the handlebars seem to be too far forward. Hub gears could be used but this will add up more weight. Dureillier style gears are light but mean an exposed chain which is not good when folded in crowded places. My problem is that I am now too old, but when I was younger, I was much more interested in other wasteful pursuits.

Edited By Alan Jackson on 10/04/2019 11:59:03

A Smith10/04/2019 12:13:30
40 forum posts
3 photos

What an excellent piece of work!

ega10/04/2019 18:50:06
1752 forum posts
152 photos

More than a step ahead!

Given the expense and complication of the patent process, I assume you are serious about production. Your experience of the main stream bike industry is fairly typical I think. At first sight, your vastly impressive design appears to use only two standard items ie the saddle and one pedal (? brakes and bar grips).

I think that 50" would be OK for some of the purposes mentioned by John Olsen but a utility folder really needs mudguards and luggage capacity.

I like the rectangular seat tube which does away with the need for radial adjustment when unfolding.

Position on bike is both personal and use-dependant. It looks as though the rider on your machine will be sitting almost directly over the rear wheel; how does it perform on hills?

Those elegant disc wheels are no doubt your own design and manufacture. I did wonder about their lateral stiffness.

I hope you will keep us up to date with your progress in the refinement of this most interesting project and perhaps post a video of the folding process.

John Haine10/04/2019 19:35:27
3183 forum posts
172 photos

The way the handlebars fold looks as if inspired by a yoga pose! A very nice design and nicely executed.

Roderick Jenkins10/04/2019 20:45:30
1898 forum posts
489 photos

One of the problems with small wheels is hysteresis losses in the tyres so you need to overcome this with high pressures. Alex Moulten overcame this problem by introducing suspension. With the design above I forsee a rather uncomfortable ride with the upright seating position above the rear wheel.


not done it yet11/04/2019 02:10:32
4748 forum posts
16 photos

It likely needs a lightweight battery, and a motor in the wheel, to get a new start project noticed these days!

Perko711/04/2019 09:27:00
338 forum posts
24 photos

thumbs upthumbs up

Alan Jackson11/04/2019 10:52:48
197 forum posts
82 photos

Hi ega, Rod, John, not done yet, perko7, and all

I had to go through the patent process just to be able to show it to others. It is a necessary requirement, otherwise nobody is interested and/or will copy if they want: that really only suits big industry, so unlike the copyright process which costs nothing can be drawn on a fag packet and now lasts 70 years the world over. The whole bike has been reduced where possible. The wheelbase is minimalised. The rider is positioned midway between the wheels and there is little tendency to tip backwards over the rear wheel without intentionally trying to. The pedal crank length has been reduced allowing the whole bike to be lower while still keeping the necessary clearance for the pedals etc. This means an average person can put both feet on the ground when stationary. I have included in the design provision for a gas strut to be incorporated into the seatpost support. The frame locking arrangement enables the seatpost to pivot a without affecting the locking mechanism. The wheels are disc because that is what I could make to keep them slim. Spokes or ribbed discs can be used and also be stiffer and lighter. As to mudguards luggage racks lights etc. they can all be added, but It depends on what you want. I was trying to design a minimum mode for a distance of about 2 or three miles or so. As to ride quality which is subjective I have ridden a Brompton which was ok but not wonderful. A humming bird was a hard unforgiving ride and a clumsy fold.


ega11/04/2019 12:27:11
1752 forum posts
152 photos


Thanks for the further comments and information.

Might you provide a link to the patent documents? Your point about needing to protect your design before showing it reminds me of the experience of Andrew Ritchie when he was developing the Brompton - a long and rocky road.

Gearing and crank length go together of course. I believe that cranks as short as 100mm have been used by experimenters. Being able to put both feet to the ground without leaving the saddle is a strong point for "minimum mode" users.

I take it that you could incorporate an epicyclic hub gear in the rear wheel if necessary but this would add relatively significant weight; the present low weight is a strong feature. I endorse your comment about the difficulty of carrying a folded Brompton. A motor and battery would add even more weight although the hub gear could be dispensed with for "minimum mode".

Is the gas strut intended to provide suspension? The plain bearing main pivot on the Brompton is a weak point although it seems not have hampered its great popularity. The rear suspension on the Brompton can be tuned by using stiffer or softer media. Some years ago they altered the front frame hinge effectively increasing the wheelbase by about 30mm which I think had a beneficial effect on the ride (I have owned both types).

Alan Jackson11/04/2019 12:45:33
197 forum posts
82 photos

Hi ega


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