Oh, thanks.
Sran dualdrive increases the gear ratio dramaticaly.
For my calculations, i see his setup with sran dualldrive 53t crankset and 11-? would take him up to 177 gear inches on his heavyest gear.
177 gear inches is archived on smallwhell folding bike with an regular setup with 72t chainring on front and 11t cassete on rear. Wich is very high.
To archieve 70km/h with that gearing the he should be at 120rpm cadence.
The frame would flex so mutch that i think is impossible to folding bike.
Even dahon 30 anny or other premiun terns or multons cannot hold this forces.
Pehaps with an recumbent? Or with a pod fo avoid air resistance?
My bet is that his archieve this speed at an botton of a huge downhill, not on flat.

Best,
pedro

Of course, this speed is on a downhill, I don't know anyone who can reach 70 on the flats.

On the flats with no wind I usually cruise at around 28/30kph, although I can sprint for a short time at 38kph. No need for a DualDrive to achieve this speeds though.

Folding bikes can be quick, but the term quick is relative. I don't ride a folder for it's speed, I ride one so I can take it with me on the bus or train (I don't have a car). I can get around quickly enough on a folder, but for very long rides at a consistently high speed, I will use my old road bike. I used to do almost all of my regular riding on my folder, until it was stolen last month. Now that I have to do my commuting on my road bike, I find that it takes nearly half as much time as it did on my Brompton. But, on the other hand, I can't take my road bike on the train or subway, so I am not going out to the countryside as much as I was.

If you are going to get a folder, speed should not be the main priority. You should choose a bike which is reliable, reasonably light, folds quickly and easily, and has a wide enough range of gearing for the type of riding you will be doing.

120 mph ......

well ....I passed a truck and got carried away

my bike in the trunk , obviously


thor

My folder is a Tern Verge X30h. I bought it specifically for the speed. It has the SRAM dual drive which makes up for the 20" wheels. My daily ride is a Kona Jake ( my commute is a mix of gravel and pavement) and the Tern is a faster ride on pavement. I bought a folder for exercise when on my frequent business trips and so I didn't want a commuter but something to get some speed.

The dual drive is definitely the key to this. Unfortunately this is significantly above the OPs budget.....

I may have to get a SRAM Dualdrive on my TernJoeP24. It sounds perfect,...

Somebody must have done a trans-Atlantic flight with their folder...

From the Moulton web site: 1985-1986 - In the Autumn of 1985, at the International Human Powered Speed Championships, a fully-faired Moulton ridden by Jim Glover broke the 200 metres flying start speed record, at 50.21mph (80.79kph). Then on August 29th 1986, at the same event, he broke his own record at a speed of 51.29mph (82.54kph) which still stands today for the conventional riding position. The Moulton ridden was an AM SPEED with the fairing designed by Doug Milliken of Buffalo, NY.

Thank you all who have shared this info. FYI, I ended up ordering a Crane 8. It seemed to come closest to what I was looking for (at least according to the descriptions!) -- and I do have 2 weeks to return it if I don't like it.

BIGGER HILL @ 42mph: 42 MPH on a Brompton! @ The Path Less Pedaled !!

Looked like fun!!! Thanks,... :thumb:

Loving your work Fietsbob :0)

On cadence 90rpm is a reasonable pace and the most efficient on the flat I was told by a v experienced coach. 160rpm is doable for some and it depends on any differences in the lengths of your legs. The more symmetrical you are, the less this induces a rocking motion which destroys rhythm. Personally I can do about 130rpm, which equates to 35mph on my Chameleon and no I don't need a hill for that, just a gel :0) it would go faster if I changed the top gear and did some training. If you want to improve your cadence start riding a 700c fixie on medium gears (eg 44x17).

Theoretically a small-wheel bike sees increasing effects from bearing friction as it gets faster, in comparison to more conventional bikes. In practice any decent hill will show you this effect is outweighed by aerodynamics.

BTW Terminal Velocity is zero, when you think about it ;0)

SRAM is a brand name. The 11-32 "cassette" means your smallest gear in the back is an 11 tooth, and your biggest is a 32 tooth. 52x11 means you're in the 52 tooth chainring (big one up front) and the 11 tooth gear in the back (small gear.) RPM is well, how fast you're pedaling, also known as your cadence.

There's nothing stopping you from going fast on a folder, that's just down to gearing. However there is something stopping you from going fast safely (or at least stably) on a folder. And that's mechanical trail.

Mechanical trail is the degree to which the front wheel acts like a swivel caster, that is, the degree to which it resists being turned and only wants to point forward. Various factors influence mechanical trail, but for small wheeled bikes really only one of them is dominant: the wheel size. All other things equal, the smaller the wheel, the lower the mechanical trail.

There are reasons you'd want to have a low mechanical trail: notably if you're planning on loading the front wheel with heavy stuff (like a porteur bike or a bike with heavy front panniers on it). But without this, low mechanical trail just makes the steering feel unstable. Small-wheeled folders are notoriously difficult to ride no-handed, for this reason. There are claims that low mechanical trail can make a bike more "nimble" for serious racers, whatever that means. But for most people, I think it's safe to say that they're far harder to control at high speeds in anything but basically a straight line.

So while it's *possible* to ride over 40 miles an hour on a Brompton, it's rather difficult to do so stably (and safely I think) compared to doing so on a racing road bike.

Mechanical trail is still not well understood? It's the distance between the steering axis and the tyre ground contact point. So a larger wheeled bike is a greater distance. But a lot of trail also makes for increased wheel flop. I think there is a bit more to it than this. Maybe this is a factor for very small wheeled bikes and in my experience there is a big difference between 2o inch and 16 inch wheels.
There are other aspects like rear wheel caster effect, (long wheel base).
On a brompton I feel the unstability is due to the lack of stem extention. Extend the bars on a bromptom. By lowering bars and extending them 9 inches(see my threads)and it's the best handling 16 inch bike I have ever ridden. Do the same on a short wheeled mezzo with an already extended stem and it's very wobbly indeed.
Simple answers rarely work.
I believe the truth is that often small wheeled bikes are not optimised for handling in their design. Brompton is a good case in point. It's so much better with more stem reach, but it's designed to fold with out any. The folding aspect dictates.
Moultons are very stable at silly speeds, they are optimised for handling.

You also have to take into account the gyroscopic effect of a spinning wheel. A larger wheel is more steady as the the increased circumference generates greater leverage. When I switch between my folder and my road bike I can always feel the difference in effort as I steer or lean over. The road bike, even at slow speeds, requires more effort do turn, not from trail (known as caster), but gyroscopic effect. This is also the main reason that small-wheeled bikes are much harder to ride hands-free.

I'd add in planetary orbital and rotational velocity, to the speed of a falling body ..

It's that sudden stop I'd REALLY be worried about,...:p

I believe all the gyroscopic stability theory of the wheel spinning to keep a bike stable was completely debunked in the 80s by demostractions that bikes with contra rotating and 90 decree off set were all perfectly rideable.
I believe modern thinking is that rear wheel castering and the general rpm of the wheels yields the stability to be able to cycle.

Meanwhile, a folding bike going faster than the speed of light would require an infinite amount of energy to slow it down. Einstein tachioned this to the general theory of not getting on with his relatives. I might have not been listening to this physics lesson properly. Anyone seen my cat, hope he's ok.

Gyroscopic effect is not fully responsible for keeping a bike stable, but it plays a large part. You can experiment yourself, take a road bike wheel and a smaller wheel, spin it, and hold it at one end of the axle. The larger wheel will be more stable. Hold both axles and try to lean the wheel to either side, the larger wheel will be harder to lean. It is not rocket science. Ride a bike with small wheels, and one with full size wheels, and you will notice the difference in the effort it takes to turn the bars. It is not a matter of trail, spin the wheels with the bikes on a stand, and try turning the bars, you will notice the difference in effort.

I have spent time racing bicycles and motorcycles, and have felt the difference in gyroscopic stability when tires and wheels of different weights are used, though the steering and suspension geometry remain the same.

Um, what? Mechanical trail is very, very well understood.

Do you have any evidence of this? And once again, high speed in a straight line isn't of interest to the discussion.

Ok.
Let me pedant.
Mechanical trail importance in bike stability is still of a disputed importance compared to other factors. That's well evidenced on Internet.
Gyroscopic force applies in equal extents reguardless of wheel size at a given speed if the distrubtion of weight is spread relatively. I may have made that up?

Riding a borrowed Moulton is proof enought to me that they are stable at speed.

Anyway answer to OP is my black 16" mezzo has done 30+ mph on the flat on the A1.
Fast enough.

Let me be *more* pedantic. Mechanical trail isn't a bicycle thing. It is a physical property that has a basic effect on practically every steered vehicle in the world. It is so well understood in terms of stability that entire motorcycle companies are built around it. Heck, Mazda toyed with the suspension system of their 2015 Mazda 3 specifically to add more mechanical trail: they have entire engineering videos about it. Whole caster systems rely on it in industry. The effect of mechanical trail on bike and motorcycle steering stability is exceptionally well understood regardless of what you may have read on the "internet".

I think it's very well established that low trail bikes are much more challenging to control at high speeds except in straight lines and gradual curves. And that *definitely* goes for the Moulton.

But yes, gyroscopic forces have been proven to have essentially no effect in a bike.

Its better stated as an actual measured dimension..

Well I feel like an ass, who would have thought you guys would have been talking over here about the same damn thing for days. Note to self read every trending thread before posting.

Ok well I have stated my 2 cents in my seemingly redundant thread but I will breifly summarize here so I am on the record:

I have 2 bikes near identical geometry, same wheel size, and same tires. One is far more stable at higher speeds much less twitchy feeling and much easier to ride with no hands (i dont usually like to grandstand like that though). The only real difference i can find between the two is the Mechanical steering trail, the smoother one has 45mm of trail and the twichier one has 35mm of trail. All the info I have found online says that most road bikes try to hit the 50mm-65mm trail number.

I should also state that on both bikes though they are both 20" wheels they have very heavy tires (770g maxxis hookworms) which would give them much more rotating mass increasing the inertial gyroscopic effects though I havent notice any significant stability effects on the bike when swapped for my schwalbe kojacks which knock about 1 pound of rotating weight off each wheel.

On a side note I am upset that many bike manufacturers these days and pretty much all folding bike manufacturers don't provide geometry infomation about their bikes. At least armed with a little info you can make some intelectual comparison before you put so much effort into finding a place that you can test a bike or in the case of folders where many times you have no choice but to buy it online.

Well, thanks, y'all. I bought an Origami Crane, still in the 2 wk test drive, but for the most part pretty pleased with it. Riding it I'm experiencing (and thus better understanding) much of what you have been talking about. What should have been obvious--but for me the beginner was not--is that the higher gear ratio in fact means higher energy output to get to those higher speeds. I guess I should have figured that. I maintained about 70 rpm on my old 3 speed comfortably and wished for overdrive. Now maintaining 70 rpm--on the exact same stretch of road--in 8th gear on my Crane is just more work.
Mechanical trail is a concept I have also gotten acquainted with. My Crane "feels" less stable than my old bike, but MT explains why.
Something that no one has mentioned is, uh, maybe the technical term is "over the top"? I.e., when I brake suddenly, I tend to do front wheelies. Thinking about it it, I should have expected that, too, but I didn't. That will take some adjustment.
This is a very educational forum!

Well that tendancy to go over the top is a large component of riding position and possibly a shorter wheel base. I have really learned to appreciate a small road bike seat being able to extend my arms and slide my ass back past the seat to bias my weight back, it took some getting used to but now that is second nature for me.

Xhim has made his choice, but I'm surprised that no-one came on board to mention www.downtube.com - Yan's 9FS is pretty solid all around, and at $499 currently, might have been a front-runner. Confirmation bias: I own one.

Glade the OP is happy with the bike they ended up getting. A bit of banter about tecnical stuff is ok if in good spirit. I learnt a lot here. I also realised my tecnical points were about slow speed stability not high speed.
Re recomeding a Downtube. I did post a photo of one. Nearly a recommendation.

I have hit 55kmh on the flats with my 20 inch wheeled folder... this is where I max out the 53/11 and can't spin any faster. My pleasant cruising speed tends to be in the 30kmh / 18mph range and that applies to pretty much all my bicycles.

The wheel size has much less to do with things than does conditioning and aerodynamics, my folder and smaller wheeled moulton both have drop bars and fit like a conventional road bike,