SesameCrunch

I was going through the Dahon website and found the following description of their HammerHead's small wheels:

"Small wheels are slightly higher in rolling resistance, but they are also inherently lighter, faster to accelerate, and most importantly, more aerodynamically efficient. Compared to the fastest 700c race bikes, the Hammerhead gives up a bit of speed but oh my, is this bike ever easy to transport."

But the whole premise of Alex Moulton's research is that high pressure small wheel offer less rolling resistance and are more efficient. Not to mention less inertia and less wind resistance.

So, given these two very contradictory positions made by prominent small-wheel bike manufacturers, what's a poor layman folding bike fan supposed to believe?

Discuss....

downtube42

not either one of them, because they lack objectivity.

I'd want to see data, not opinions. And not theoretical data on wheels, but actual data from complete bikes.

But I'm too lazy to look it up, so I'll go with my opinion that small wheels are bad (including the one one front of my V-Rex).

arctos

Tony Hadland's book the Moulton Bicycle includes the comparative testing of full sized wheels and small 16 inch ones using identical pressure and tire type. These lengthy tests led to the Moulton view of small wheels listed in their Q&A section quoted below:

1. Why the small wheels? The small wheels are an essential feature of the Moulton concept. They offer many advantages.
With only half the rotating mass of the wheels on a 'conventional' bicycle, it is possible to accelerate faster.
They are extremely stiff and much stronger than larger wheels because of the short spokes.
The aerodynamic drag is lower; there is less frontal area and less spoke area causing turbulence to slow you down.
The centre of gravity is lowered, resulting in improved stability.
The small wheels free up space normally occupied by large wheels, allowing luggage to be carried lower. 2. Aren't smaller wheels harder to pedal?
No, because:-
The gears are chosen so that they correspond to pedalling a bicycle with large wheels.
The smaller frontal area results in less aerodynamic drag.
The lower inertia means that you can accelerate faster.
If you are still doubtful, consider the HPVs (Human Powered Vehicles) developed for the ultimate performance - many
of these use the unique 17" Moulton wheels and tyres fitted to the AM series bicycles. 3. Why the space frame?
The construction makes it far stiffer and stronger than conventional frames.
The weight is similar to that of the best conventional touring bicycles - and the Speed model is comparable with the
lightest racing frames. In conjunction with the small wheels it results in a low centre of gravity.
The standard frame size can be ridden by cyclists of almost any size.
The low top tube leads to improved safety and controllability.
The low top tube allows it to be ridden equally easily by men and women; it is also a major advantage for elderly or
disabled riders, who cannot easily ride conventional bicycles. 4. Why suspension?
It allows the advantages of the very rigid small wheels, high pressure tyres and space frame to be enjoyed while giving
a much more comfortable ride than a conventional large-wheeled bicycle. The road shocks experienced on a conventional bicycle are dramatically reduced.
It is a light, simple, maintenance free system.
Improved traction - the wheels do not bounce going through corners or on rough surfaces.
Reduced strain on the wheels - the wheels stay true, spoke nipples stay tight and spoke breakages are extremely
rare. 5. Does it fold?
No - this is a no-compromise high-performance bike, quite unlike any folding bicycle.
But ...
The frame does separate into two parts.
This does not affect the frame rigidity - tests on a brazed-up version of the frame against the normal separable version
showed no difference in rigidity. When separated into the two parts, it easily fits into the boot of a car.
When placed in the carry bag, it can be carried on a train as hand luggage, rather than needing to be placed in the
luggage van of the train - a big advantage given the restrictions on some train services. Users have also transported their AMs as normal luggage on aircraft flights. 6. Is it as good as a conventional bicycle?
It's not just as good as a conventional bicycle, it's better:-
Owners of Moulton bicycles report that after using the Moulton for a week, they never want to ride conventional
bicycles again. Just look at the specification and the performance details. 7. How well does it perform?
An AM bicycle holds the world speed record for bicycles of conventional riding position at 51mph, fully faired.
The AM bicycle has successfully completed the Race Across America (RAAM) - finishing the course of 3117 miles in
10 days 15 hours and 1 minute. Owners of AM bicycles use them successfully for commuting, touring the world and for racing. The APB bicycles are
ideal for commuting, touring and use off-road.
My own real world experience over 20 years of owning several F frame Moultons, an ATB and a Mark 3 seems to confirm at least equal rolling resistance. I do also confess to riding and owning full size bicycles-a touring bike and a mountain and road tandem.

makeinu

Two things:
1. I don't think Alex Moulton purports that small wheels have less rolling resistance. It's that small wheels are lighter and more aerodynamic, while suspension provides low rolling resistance.
2. Dahon doesn't specifically say that the Hammerhead's small wheels are what makes it slower than the fastest 700c race bike. Moultons are also slower than the fastest 700c race bikes and the fastest 700c race bikes are slower than the fastest small wheeled recumbent bikes. Aside from being visually striking, wheel diameter is a minor factor in all respects.

I think the entire concept of one bike being unequivocally faster than another is hogwash. It's a case of horses for courses and a 700c race bike will always be faster than a small wheeled bike in a UCI race because small wheels aren't UCI legal.

yangmusa

Close. Suspension lets your run narrow, high pressure tires with low rolling resistance without sacrificing comfort. You could run the same tires with no suspension, but it would be a rough ride.

EvilV

I think that all of that was born out by my experience of owning and riding the TSR30 that Sesamicrunch now owns and rides. I found that the bike did what Moulton says on the tin - I rode faster and longer than on my other folding bike, and the suspension not only made the bike more comfortable, but the road holding had to be experienced to be believed. It would literally fly over the bumps and I could pedal through the roughest of normal roads with absolute confidence at speeds I wouldn't have expected.

Sesami will no doubt say what he thinks about the arrangement. He has a much wider experience of bikes than I have, but I never felt that bike was slow.

I agree completely.

makeinu

It's the same thing really. All rolling resistance is theoretically due to surface roughness. So it shouldn't be surprising that if a ride is too rough your tires get bounced backwards, thus, increasing rolling resistance. The only way around it (literally) is for the wheel to go up, which can be accomplished with either a larger diameter wheel or a wheel with some give. The former is heavy and has poor aerodynamics, while the latter needs to flex. Since tires have conflicting demands of traction, wear, etc, they cannot be completely optimized for low hysteresis and, thus, waste a lot of energy flexing. A dedicated suspension, however, can flex with minimal losses.

So suspension lets you achieve low rolling resistance without sacrificing weight and aerodynamics.

jur

I have this differently: The wheel size is negligible in rolling resistance (Moulton's findings), the tyre pressure dominates. But the smaller wheel is harsher, so enter suspension to counter that.

But now, another parameter enters the equation - rolling resistance is now actually decreased due to the lessened effect of rolling over small bumps - instead of the whole bike+rider being lifted over a bump, the suspension flexes and just the wheel has to go over.

EvilV

Excellent explanation Jur - and brief too.

timo888 

But the site goes on to show how rolling resistance is negligible in relation to other resistances.

Also, wider tires have less rolling resistance than narrow tires...when both are inflated to the same pressure. But narrow tires can be inflated to higher pressure.

From the Schwalbe site.

SesameCrunch

I, too, tend toward the Moulton theory (but that may just be cognitive dissonance, since I own two Moulton bikes ). The mystery to me is why Dahon's official website would concede that small tires are intrinsically inferior in rolling resistance? What studies have they done, I wonder? Pretty poor marketing, I'd say....and I'm a SmoothHound/Hammerhead fan!
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On a totally different topic (is it kosher to hijack your own thread? ) While I was changing over to the Capreo setup on my SmoothHound, I took a ride with the stock 55t chainring and the 9-26 Capreo cassette. I had the bike over 41mph (downhill) and was still pushing gears with the 55/9 combination and 20" wheels. It was exhilarating to say the least! I had to quit at 41mph because of road conditions, but there was still room to go on the gearing! Crazy fast. Now I have a very happy setup with 53/39 in the front.

Mooo

and that's why a Rocket is faster

timo888 

The Schwalbe site explains such an assertion: given the same inflation pressure, a tire of a specified diameter will be less out-of-round than a tire whose diameter is smaller. The absolute "squish" or deformation area is the same for both tires, but the tire with the larger diameter, and thus having the greater circumference, has proportionally less deformation, i.e. is less out-of-round than the smaller. The more out of round, the greater the resistance. The larger the circumference, the more gradual the ascending arc of the tire; the smaller the circumference, the more abrupt the arc. To state the thing in extreme terms, if you had to fashion a wheel made out of wood in a polygonal shape, would you rather ride a small pentagon or a larger duodecahedron?

Let's say the rims are the same width, and that we have two wheels, one 700mm Ø and the other 305mm Ø. We will ignore the tire wall height for the sake of simplicity. The circumference (Π * Ø) of the larger is 700 * 3.14 = 2200 (roughly) and the circumference of the smaller is 305 * 3.14 = 958. If there's a 25mm deformation along the tire surface, on the larger that is 25/2200 (.011) and on the smaller it is 25/958 (0.2), about double.

Regards
T
P.S. But again, as was mentioned on the Schwalbe site and by others earlier in the thread, at higher speeds, air resistance is far more important than rolling resistance, and smaller narrower tires offer less air resistance, so what little the small wheel loses in rolling resistance it more than makes up for in large reductions in air resistance -- if it's a narrow tire.

P.P.S. But none of these nuances makes any meaningful difference unless you're racing.

SesameCrunch

But Moulton proved through more than 500 test cycles with actual bikes that his 16" wheels rolled better. I'd take that empirical evidence over some theoretical calculation of deformity.

kb5ql

Has winter come early??? It's too early for the fear and self-loathing threads.

I still need to see this mythical TSR and challenge it to a race.

Sir, the gauntlet has been thrown.

jur

Or, I'll see your TSR and raise you a Swift.

stevegor

I have a R20 three of a kind...that beats the lot of you.

EvilV

But would you be testing the bike or the man who was riding it?

timo888 

Could you provide a citation/link? I am under the impression that what Moulton showed is that smaller-diameter wheels with narrow high-psi tires have less air resistance, not that they have less rolling resistance. Predications involving two variables may lead to some confusion: larger wheels with low-pressure tires have more rolling resistance than smaller wheels with high-pressure tires. But if the tires are inflated to the same pressure, the larger wheel wins but only with respect to rolling resistance. The small wheel wins with respect to air resistance.

If you'll consult the Schwalbe site, you'll see from their graph that rolling resistance is by far the least important of the various resistances: air, gradient, and rolling. [Not much friction resistance in a properly maintained bike.] The smaller wheel's aerodynamic benefits at speeds above 20 km/h are far more significant to overall performance at speed than the slowing effect of its greater rolling resistance, vis-a-vis a larger wheel with tires inflated to the same pressure. Below 20km/h, air resistance and rolling resistance are of roughly equal importance (see where lines 1 and 3 cross).

Key to Schwalbe graph (x-axis shows speed, y-axis shows resistance):
1 Rolling resistance
2 Gradient resistance
3 Air resistance
4 Total resistance (1+2+3)

Regards
T

jur

How about a Mini, R20, Yeah, Birdy and Swift full-garage?

SesameCrunch

Challenge accepted!

Me on the TSR and you on the XtraCycle with the two kids, right?

The winner would definitively prove whether small wheels are faster or not (I think).

itsajustme

The problem with trying to test it empirically is that the premise is false. That is, the definition of rolling resistance precludes a single configuration from having lower rolling resistance over all terrain. So if you try to interpret the results of an experiment as determining whether one size is inherently superior to another you can always conduct another experiment over different terrain which gives you a contradictory result.

You see, rolling resistance is defined by the force which pushes backwards from the road surface as a wheel rolls forwards. There are two ways for this to happen:
1. If you're rolling over a surface which suddenly turns up 90 degrees and becomes a wall then the force of rolling resistance will be whatever force necessary to stop a mass moving at your velocity as you hit the wall. Wheel size, tire material, tire pressure, etc, won't have anything to do with it.
2. If you're rolling over a perfectly flat, perfectly smooth surface then the tire and surface will both deform into little bumps (ie miniature walls) which, in turn, push back against you as you crash into them.

Rolling resistance on real surfaces will obviously be a combination of the two. A soft wheel reduces #1 and a hard wheel reduces #2. So the configuration with the lowest rolling resistance on real surfaces will depend on the smoothness of the surface and shape of its permanent bumps.

That being said, I think the key to the Moulton concept is that both a large wheel and a suspended wheel reduce both #1 and #2 and since adding a suspension is both lighter and more aerodynamic than enlarging a wheel, small suspended wheels involve fewer compromises on typical road surfaces (although one can still find scenarios/experiments for which another configuration is better).

SesameCrunch

I heard that reference in a Youtube video with Dr. Moulton that was about 10 minutes long. A quick search just now didn't yield it. I'll see if I can't find it later.

Regardless of whether the claim of faster small wheels is due to lower rolling resistance or other factors, I am still mystified as to why Dahon would say that small wheels are slower in their marketing pieces....

makeinu

Well, they also sell a number of bikes with "full size" wheels.

timo888 

Mystified because you'd expect advertising hype never to include such a comment ... or mystified for technical reasons? Also, they don't say it as bluntly as you do. They say the Hammerhead gives up a bit of speed to the fastest 700c racing bikes. And they make up for that with an "oh my".

Regards
T