This is a good article on the Moulton small wheel philosophy. Well, part philosophy, part science...

https://www.users.globalnet.co.uk/~hadland/page15.html

The end conclusion? Suspended, tuned bikes with the right tire pressure on smooth road conditions will outperform large wheels. Otherwise, large wheels have an advantage due to lower rolling resistance. I think I understand the concept now; pebbles, etc., tend to push back on tires with a smaller contact patch and higher pressure. Kind of the way that 1970s skateboard throw you off if you hit a pebble because the wheels are so hard. Softer wheels deform around rough surfaces, so there is no push back.

Thus, if you are on a rough surface, you will go faster with larger smooshy tires. If you are on a hard, smooth surface, you will go faster with hard, small tires b/c there is less deformity.

This issue is very polemic with science giving advantage to a bigger wheel and emotions giving advantage to small portable wheels. One thing is for sure, I rode side by side with road bikes until we reached the first descend. I lost control of the front wheel and I add to slow down. And as the article refered I am within the limits 300 mm - 500 mm with 451 mm wheels 28 mm tires 110 psi. I have no doubt bicycles with bigger wheels are more stable.

Also may be of interest:

https://www.ingentaconnect.com/conten...2?crawler=true

but has to be bought. "An important finding was the ability for a streamlined bicycle under certain conditions to sail" sounds interesting!

https://www.diablocyclists.com/bicyclescience.htm

https://bike.terrymorse.com/rrdiscuss.html

For a humorous look at small wheels, & folders:

https://www.citycycling.co.uk/issue5/issue5page3.html

Stability of a bicycle is more a function of the geometry than the wheels size. My Raleigh Twenty is ultra stable, it is like it's on rails. I routinely get 70km/h and over without the slightest problem. But you can't do that on a stock Twenty - the geometry is iffy. My Swift is less stable than my Twenty.

Check the Speed Wobble article on wikipedia.

Can you ride your twenty with no hands?

Yes.

The problem with the discussion is it does not discuss $. To design a properly suspended bike that mimicks a full sized would take allot of engineering skill and perhaps parts like adjustable shocks that don't exists. The world is not looking to spend $1000+ on a bike. Dahon Mu XL is a nice attempt at such a bike ($900).

I'm glad this question has come up because it's something I was pondering the other day as I was riding my Mini.

When I was a youngster, I could ride my 20" no name bike no-hands, no-problem.

I can't ride my 20" VIIIH no-hands at all (to say nothing of the Mini - I wouldn't even try it).

So what's the deal. Is it me at more than double the weight and 1 to 2 feet taller or is it the bike?

If it's the bike, why? What's different between my folder and my 1970's stingray?

By the way, I can see there is a difference, I'm not blind. I'm asking for the technical / mathmatical reason.

Shorter wheelbase = less stable?

I can now ride a Brommie no-handed, but it took me a while to get a feel for its characteristics. The faster I'm going, the easier it is to control. Any slight reduction in speed and "pedal steer" easily shifts the bike all over the place. I'm using Marathon 1.5s but I don't know if tire width makes a big difference.

Polaris, it's not just you. I can just barely ride my Mini with no hands, but don't; it's not stable. I cannot ride my Strida, nor my Moulton Stowaway, nor my Raleigh 20 (with original fork) without hands, not even a little bit.

But I have a MTB that I set up for commuter use, and I can ride that with no hands, no problem. It's so stable I can go without hands long enough to take off a jacket and tie it around my waist without worrying in the least.

This came up not long ago in reference to this article on early Dahons:
https://www.johnforester.com/Articles...eEng/dahon.htm

According to Forester, it's not the wheelbase, but the "trail." According to the article, Forester modified his Dahon as follows:

I would like to do something similar to the Mini's fork... but not by bending it, that sounds risky!

Maybe we should start another thread, with a poll: what (folder) do you ride, and can you ride it no hands?

Rudi

Doesn't modifying the trail modify the wheelbase distance as well (i.e. he lengthened the wheelbase by extending the trail)? Seems like that's all Forrester does.

I'd be curious to try no hands on 8" wheels, but I think the center of gravity on those kinds of bikes is way too high to be stable at any speed.

I can ride my Swift no-hands--though it's less stable than either of my 700c bikes.

I want to point out that Forester's article doesn't represent all the issues associated with trail and stability. As noted by Jan Heine in most every issue of Bicycle Quaterly, traditional French long distance bicycles (randonneur machines) have very low trail, in an application where stability is a primary design requirement. In a 1200km event, you don't want to spend any extra effort keeping your bike tracking straight.

I don't pretend to understand all the issues myself, but I do know that tire width, tire pressure, center of gravity, and weight distribution--it addition to trail--are factors that need to be considered when evaluating stability. Even the term itself needs analysis, since high speed stability and low speed stability are often at odds.

Jack

Yes, good point; but I think the key is that the additional length is in the fork, rather than the frame.

I'm sure you're right, that stability comes in part from the gyroscopic force of the wheels, but it seems that's not the whole story.

Intuitively, it seems to me that a bike would handle best if the steering axis, defined by the angle of steerer tube at the headset, is a little behind the contact point, where the front wheel touches the ground. If that's correct, then a bike with smaller wheels does not need as much trail as one with larger wheels. But on the Mini the steering axis is a little ahead of the contact point. It's hard to measure, but it looks like less than an inch. On the Strida the contact point is an inch or more ahead of the contact point. But that, as I say, is my intuition... and who knows where that comes from.

Bending the forks will of course affect the wheelbase, but to get more trail, you bend the forks back, so we're looking at a shorter wheelbase here. This is sometimes counter-intuitive, but on a typical bike (including the folders under discussion), more fork rake (aka fork offset) will result in less trail.

Detailed explanation: https://en.wikipedia.org/wiki/Bicycle...cycle_geometry

The only folder i could ride no hands without even thinking about it was my Giant Halfway RS. Since then all my folders are hard to ride without hands.

My current Brompton is a mean bike: if I ride with no hands and stop focusing for a split second it will try to ride alone...

In the Velovision review of the Mezzo, I seem to recall Peter Eland saying that (whilst he didn't dare to), one of his colleagues had ridden the Mezzo no hands with some success, and put it down to the relative stiffness of the hingeless frame. Having said that, I haven't been over tempted to try it myself whilst navigating London rush hour traffic. Maybe one day on a quiet road, with soft verges all around to fall onto..

Ability to ride a bike no-hands depends mainly on the trail, ie the contact patch must be behind the steering axis' extension where it hits the ground, like in a castor wheel. Having a headset bearing that rotates freely is also nice to have.

I modified my Twenty's fork to increase trail and it made a whopping difference. Since then I have installed a RST suspension fork with similar offset, and it is also very stable.

The DT Mini suffers (by my remote analysis) of too little trail: with a small wheel, the steering axis hits the ground closer to the contact patch if the forks had no offset; so even a small amount of offset (rake) will reduce the trail. The Mini fork is raked, and has very little trail as a result, hence the difficulty in riding no-hands.

Thanks for the explanation, folks.

The gist of the wikipedia article:
"Trail is a function of head angle, fork offset or rake, and wheel size" (followed by a mathematical formula).

In response to a question, here are some pics of what I did to make my R20 ridable no-hands.

Fisrt, here is the original condition:


Here it is after cold setting the forks. I straightened them, by lightly clamping in my woodworking vise near the fork ti for each blade, and hauled away near the crown. The result was very close to what I wanted, it straightened in the most bendy part. The paint cracked.


Here it is with the suspension fork:


I can make some measurements on the original for to find the current rake, if someone wants it.

Thanks! The wikipedia article is very helpful, and it's interesting to see how my intuition is so completely wrong (because the effects of the geometry are, as you say, counter-intuitive).

And thanks, Jur, for the photos of your R20! That is one cool looking bike. I'm curious just how much you bent the fork blades of the stock fork.

Hi
I have wondered why there are no these https://www.velorution.biz/index.php?s=hebie in folding bikes -has anyone seen them fitted? Perhaps inside the steering column could be fitted some kind of spring making the same job.
When I let my workmates drive Merc, the comments were:"Nice, but unstable", it was same with my previous 20" folding-bike. It might make folding bikes more popular if they were more stable - if they were more popular there would be more competition - and improvement in quality and innovations.

Never even heard of them ... neat idea. I recall some motorcycles had steering dampeners at one point.

I also like some of the kick stands they offer. Anyone see one in the US?

I think these are more for the case of the stationary bike, to prevent the steering from rotating. I have no idea what they would do to the riding stability.

I tried riding my Swift again no-hands, and it is definitely marginally stable - I can't unwrap my muesli bar without veering all over the road.

Bigger tyres would help since from a pure geometry consideration, these increase trail by a small amount. This explains why some have reported putting on a large size tyre on the front made a good improvement.

The increase in trail due to larger tires is negligible compared to the increased self-aligning torque of the shorter/wider contact patch. If trail alone were responsible, 541 Twenties would be more stable than 406 Twenties.