mommus

Hi everyone,

I posted a similar thing on the bike mechanics section of this forum but thought I should ask the people who really deal with this stuff.

I'm working on a design for a new folding urban/light trail bike. Part of the design necessitates an upper frame that is made from two pieces, meaning that the minimum clearance between your knees (when pedalling) will be about 140mm, give or take a few mm.

Is that something you think you could tolerate? If it meant you could have a light, strong full size folder with full size wheels that folds into a space the size of a trekking backback?

All comments and opinions very much appreciated

cheers

Tom

ChiapasFixed

and what, exactly, is the advantage of "full sized" (I assume you mean 26" or 700c?) wheels?
(chuckles malevolently)

bhkyte

some old school BMX bikes had two upper cross bars.ie torker and haro not problems there.

I have seen a german bike with twin Downtubes so that the rear wheel could flip under(like a brompton) and then rest between the twin tubes. can not remember the thread name.

mommus

I've been doing a bit of street research (chatting at traffic lights whilst riding to work) with cyclists, and one of the main reasons people cite for not buying folders is that they look a bit odd with little wheels and enormous long stems and seat posts. I've tried a few bromptons and a dahon and find that the small wheels retain less inertia, so are more tiring to ride. They also feel less stable. (though I'm sure you'll all correct me on these points)

I do mean 26" wheels yes. The advantages of larger wheels must be obvious to most people or ordinary bicycles wouldn't have had 26" ones since the dawn of time?

I'd eventually like to develop a mountain bike in the same vein as the urban one i'm working on, so starting with larger wheels seems logical.

It sounds like those pesky Germans have stolen my idea then...

Thanks for the feedback, however malevolent!

bhkyte

If you do some test riding,you will find 20" wheels are fine for just about any purpose. A brompton does not have the same geometry as a 26" bike, but are common bikes. Sometimes people extrapulate that all folding bikes ride like a brompton.

this is not intended as anti brompton statement, as the bike furfills its intended role well.

Try a dahon speed pro, a birdie, a moulton a bike friday, a downtube FS ,a dahon jetstream,a dahon hammerhead. If you try any or all of these bikes you will be convinced that a bike does not need 26" wheels.

I am currently trying to get a friend who is considering taking advantage of the scrap car initiative to buy a new car to consider getting the bike to fit the car ,not getting a car to fit the bike.
I have suggested that she tried a birdie demonstrator out at the LBS. Her preconception means that she probably will not do this, yet I know the bike would be perfect for her intended use.

Its a slow process, but things will change, if you want to build a folder build a better 20" as none of them do everything well. Else try a 26" ,it may sell, but it will be less useful as a folding bike.

just my 2p.

fmattheus

Now that's a healthy attitude for someone trying to come up with a new concept

itsajustme

Not saying it wasn't more tiring to you, but it's hard to believe the reason could be inertia. The difference between a light bike and a heavy bike is that the light one retains less inertia and everyone knows that a light bike is less tiring, not more.

Moreover, if you consider the physics of the situation it turns out that a smaller wheel does not actually have less inertia unless it's lighter because the faster spinning exactly cancels the smaller diameter. So it turns out that the weight and inertia of bicycle components are equivalent and the only way for inertia to make a bicycle less tiring is for all heavy bikes to be less tiring, which is ridiculous on its face.

This is another phrase that's thrown around a lot, but I find the meaning a bit cryptic. In engineering terms there's certainly nothing less stable about small wheels, so it's difficult to say whether any significance can be attributed to your feeling apart from being a matter of taste.

Unless, of course, they reasoned like you have here that "it must be best simply because other people are using it". And if a burgeoning bicycle designer like yourself thinks it reasonable to draw such a conclusion then why would you expect greater discernment from an ordinary rider?

And, as a designer, this is the part where you realize that even if smaller wheels are better they'd have to be substantially better to make you more money than giving in to the popular prejudice, which reveals the true advantage of larger wheels: marketability and economic efficiency.

The truth is that, as toys and sports equipment, most bicycles have not been designed with regard for what's best since the invention's infancy (ie before the invention of the automobile when bicycles were still considered vehicles). Contrary to popular option bicycle design is not highly evolved, but in a state of stunted growth because although many bicycle variations have been created, most were never sufficiently evaluated before the whole of human powered transport was relegated to toy status (ie for play or sport).

To assume that whatever is popular must be best is a slippery slope. Or as my father used to say, "the masses are asses".

Check https://www.mas-design.com/ for examples of where the same train of thought has taken the design of others.

mommus

Thanks again for the extensive comments... They are all very useful to me.

In terms of stability, I would suggest that the feeling of stability I described was a consequence of the shorter distance between the tyre and the hub on a brompton. It's the same feeling I get riding my scooter as opposed to a proper motorbike. Almost a top-heavy feeling and a tendency to weave more. In engineering terms I think the flywheel effect and to a lesser extent, the gyroscopic effect of larger wheels does make a difference. At the same time, I am very impressed by Bromptons, so don't think of me as a Brompton-Hater

I agree that the statement I made about people 'using large wheels since the dawn of time' was a little backward-looking. I felt that a bit as I was writing it, but left it in anyway to guage the reaction.

I disagree that bicycles are in a state of stunted development. I think any frame-builder or bike designer embarks upon a process of evaluation before beginning work. In many respects this could be considered an evaluation of human-powered transport. I certainly embarked upon - and indeed still consider myself to be in the process of - an evaluation of human-powered transport.

My ideal situation would be a bike that can be carried in a backpack and could accompany anyone on a trip anywhere as the sole method of (land) transport, irrespective of terrian, and be equally at home in a car-boot or overhead rack on a train. You can start at any point in this design and will still arrive at something resembling a regular bicycle. Not because I'm backward-looking or basing my decisions on flawed engineering and prejudice, but simply because it is a well-evolved compromise between all the essential needs.

thanks again for your posts

mommus

thanks for the links also

bhkyte

Read the "wheels bigger than 20 are unnecessary " thread if you can find it.

I am not against 26" wheels, but they are less usefull on a folder. Most folding 26" wheeled bikes fold crudely and only one or two at the very most fit a car boot at a time. They do not go in small cars at all without folding the seats down. This is no good if you have a family.

Taking both wheels off a non folding bike is just about as effective as a folding 26" IMO, but the folder is slightly quicker and easier, that is not much as folding frames are heavier and more expensive.
There are a few small folding exceptions such as the under speced, over price,heavy "IFmode".

I dont thing that finding solutions to accommodate 26" wheels is the answer when the advantages of larger wheels are in depute other than due to market forces,
but show us what you can do.

the german bike that was mentioned is at https://www.bikeforums.net/showthread...n+folding+bike
folds= https://translate.google.com/translat...sl=zh-CN&tl=en
looks very nice.

mommus

thanks bhkyte, that German bike is a very pretty thing indeed. It also looks incredibly light.

I'd love to show you my idea, but can't until i've at least finalised the initial design and spoken to a patent lawyer. It's rather more chunky than the aforemationed bike, which again is a result of it's eventual intention as a mountain bike.

I get what you're saying about 20" and 26" wheels and I realise that there will probably be an insignificant performance advantage, but I've kind of taken on the challenge of producing something of identical proportions and geometry to a regular mountain/urban bike. The wheels themselves will reduce in size too. The folded package will be about 900mm x 300mm x 300mm including the wheels. I'm aiming at backpack size.

alhedges

+1

It's certainly possible that the OP's design will change people minds, of course, but notwithstanding the opinion of cyclists on the street, 26" folders haven't been terribly successful on the folder market. The reason being, IMO, that they don't fold down that small, especially when compared with just removing one or both wheels from a conventional 26" bike.

Because of the fact that they fold, folders are going to be more expensive and slightly heavier than an equivalent bike. (Or much more expensive and about the same weight...). This basically means that there will be a penalty for buying a folder. To make up for that penalty, people want the folding feature to be useful...i.e., they want to fold to be small enough that the folder can do things that conventional bikes can't.

Having a 26" folder doesn't offer a lot of advantages over conventional bikes when compared with 20" folders.

badmother

Why would you carry something that has got wheels? Leave bike as is and hang the backpack on the bike and roll.

I suggest you spend more time with a 20" bike, also offroad, you`d be suprised of what it can do. "Most peopel" do a lot of things that is not smart all the time, like riding full size bikes .

bhkyte

Many folding bikes already are identical riding postions and geometry to a regular mountain/urban bike.

mommus

If you had to walk through terrain unsuitable for a bike, or if you wanted to carry it on a plane, train etc. It would be nicer to pack inside something rather than having all the protruding bits scraping and catching on things. I'm not suggesting anyone treks through the Amazon rainforest with it but foldies do need to be carried from time to time, and the most convenient way to carry something heavy is on your back... well, actually the most convenient way to carry something heavy is to get someone else to carry it, obviously.

It's also got mini wheels so it can be pulled behind like a wheely-suitcase, with or without the bag.

itsajustme

The reason, IMO, we don't see more folders intended to be carried on the back is that having those protruding bits jabbing your back is far worse than having them scraping and catching on other things.

This can be solved by covering or eliminating the scraping bits, but any kind of casing or shell will make the bike so heavy that it defeats the purpose of carrying it on your back and unless all the parts are custom made there will surely be many such bits. So there are weight and cost constraints.

There's also the issue of how far the bike protrudes behind the back. A very thick pack pulls more backwards than down and taxes the stomach muscles more than the back muscles, thus defeating the goal of using the strong back muscles to do the work. It's very difficult to build a thin folder...particularly because of the bottom bracket and pedals. Perhaps a Gram Obree style washing machine BB would help here, but so far no one has tried it and it still doesn't solve the jabbing problem.

BTW, speaking of Gram Obree a lot of his design elements are either the same as or improvements for folding bikes (monotube frame, smaller Q factor, etc) and are faster to boot. I'd like to see old faithful redesigned as a folder and I'd be surprised if Rob English hasn't had the same idea:

AEO

the only thing it really needs is a good handle for rolling around.

if it has any 16" or 20" wheel, it'll be easy to roll it up stairs as well.

for me, I'd rather not have to carry it at all.

bhkyte

Just seen advert fot Bigfish , Nexus 3 speed (undergeared?) ,Older Diblasi sized(?) folder, may be simular idea. frame does not fold rather like a micro bike. Some good concepts, but needs a folding frame I think.
https://www.bigfishbike.co.uk/index.a...atalog&c=13643

bhkyte

correction, looks like the rear frame slides forward to reduce the packaged size. If they combined this with the half way design of singled sided forks and rear stays it could have gone very compact indeed! with an angled fold like a mezzo or birdie. Just occurred to me that's what the "IFMODE" is.

Twin triangled frame without a high flexy seatpost that folds as compact, (or more than), a Brompton could be a market leader. and remove the prejudice of conventional over folding beam frames.

Pine Cone

I've ridden bikes where I have either thin bags on the top tube or tied stuff on there and I think after about 80mm I tend to knock my knees on whatever it is. I could tolerate 100mm, but I think 140mm would be wide enough to be very annoying.

prathmann

Agreed. I've noticed the same thing when I've carried items that increased the effective width of the top tube area of the bike. But individual pedaling styles vary and some riders always keep their knees well out to the sides so presumably they would find it acceptable. Personally I'd much rather have the smaller wheels and no impediments to keeping my knees fairly close together while pedaling.

I do notice some drawbacks to the smaller wheels on my folder. The tires wear out more quickly and tend to be somewhat more expensive due to lessened competition. And, if other factors are kept equal, they have slightly more rolling resistance. Normally this is small enough to be negligible, but I notice that if I let the pressure drop it makes my folder feel much more sluggish than the same pressure drop in the fullsize wheels of my other bikes. But keeping the tires pumped up isn't really a big problem. Smaller wheels also don't negotiate bumps quite as well - leading more small wheel bikes to adopt suspension systems. I haven't found it to be a real issue with 20" wheels, but much smaller and they do start to give a harsher ride.

And there are benefits as well. Despite the OP's claim of wanting more inertia, the universal quest of cyclists and cycle makers is to minimize inertia - both of the bike as a whole, but particularly of the rotating wheels. Since smaller wheels of equal strength can be made lighter, this is an advantage. The smaller wheels also have less frontal area and therefore reduced air resistance. And air resistance is further reduced when riding in a paceline since it's possible for the rider of a small-wheeled bike to get closer to the rider in front.

ChiapasFixed

"My ideal situation would be a bike that can be carried in a backpack and could accompany anyone on a trip anywhere as the sole method of (land) transport, irrespective of terrian, and be equally at home in a car-boot or overhead rack on a train."

then by all means, consider 20" or 16" wheels.

"The wheels themselves will reduce in size too."
This could be really interesting, as long as the weight and performance penalty is not severe. Another issue is replacement parts in far off places (like the Amazon).
Also, if you can reduce a 26" wheel enough to fit in a back pack, imagine the same technology on a 20" wheel that really reduces down to a manageable size! You could really be onto something then.

"Part of the design necessitates an upper frame that is made from two pieces, meaning that the minimum clearance between your knees (when pedalling) will be about 140mm"

I would strongly caution against this, as any cyclist who needs to go a fair distance without damage to the knees will want to pronate, or "toe-in" a bit, and bring their knees as close as possible to the top tube. In fact, on of the really nice things about most folding bikes is the complete absence of a top tube, giving the rider more freedom of movement, and easing mount/dismount.

ChiapasFixed

have you had a good look at the high performance, packable/folding all terrain bikes out there? examples are: Airnimal Rhino, Pacific Reach, Moulton TSR, Bike friday Llama, Airnimal Joey, Swissbike, Tikit, Birdy... the list goes on and is growing. Each bike is best suited for different things, and I appreciate wanting to make a "do it all bike", which is pretty much what I was striving for with my Tikit, just make sure you are not re-iventing the wheel!
....or is that precicely what you mean to do?

mommus

As ever... all comments greatly appreciated.

I too am getting rather concerned about the width of the frame, and might ahve to think about redesigning the fold (again). But I suppose this is the essence of design isnt it. Trial and error.

I am actually trying to re-invent the wheel... gulp. Maybe I've bitten off more than I can chew

mommus

Have gone back to the drawing board this weekend to address some of the points mentioned above... specifically the wide frame