EvilV

I think this may be the video you speak of Sesamicrunch. It is on Google Video not Youtube.

https://video.google.com/videoplay?do...2343&q=moulton

Watching that was what drove me to buy the TSR and then tempt you with it.

Anyone watching will have to be grown up and ignore the atrociously boring lecturer's voice over. It looks like some Engineering Prof voiced it (very tediously) but it refers to this subject as I recall.

invisiblehand

I always thought that the Schwalbe website was quite good.

One problem with saying that air resistance is most important is that for many people, they can't make their aerodynamics much better. That is, if a person is concerned about speed, chances are they have already optimized -- to some extent -- their riding position and left the panniers at home. From what I gather, past that, the biggest improvement one can make concerns rolling resistance.

SesameCrunch

Yup, that was it. In it, Dr. Moulton clearly states that his test yielded that small, high pressure tires offered the best rolling characteristics. Then, he designed the suspension to smooth out the ride.

Thanks, EvilV. I watched the whole thing again. Interesting video.

SesameCrunch

I'm mystified for technical reasons. Having drunk the Moulton Kool-Aid, and knowing that he's a quintessential engineer, I trust his analysis. On the other hand, Dahon completely concedes that small tires are inferior without offering any analysis behind it.

EvilV

Moulton spoke of small wheeled bikes using a couple of percent less energy. I got the feeling that he did live tests with a rider. I'm envisaging some dude riding along wearing some kind of breathing apparatus to measure his oxygen burn. It would be just about the only way to do it I think - but then; a) I'm using my imagination and not engineering expertise, and, b) I'm as far from being an engineer as being a space man,

fmattheus

I just watched the video as well. At what point does he actually say that smaller wheels offered better rolling characteristics?

At 2:00 he says "the inflation pressue really dominated the rolling resistance, not the size"
He goes on to mention that smaller wheels would be bumpier, and needed suspension to smooth it out.

SesameCrunch

starting at 3:50.

invisiblehand

Tire technology might have been different at the time of testing. From what I recall of the video, Moulton talks about historical tests as opposed to what is currently available. It may be the case that small thin tread and supple sidewall tires were easier to make the big ones. Things might have changed since those tests.

timo888 

It's a beautiful bike but the Kool-Aid isn't as delicious as you remember, and I think you're conflating a couple of different factors.

Rolling resistance, air resistance, gradient resistance, and friction add up to overall resistance. Schwalbe identifies air resistance as the dominant factor in overall resistance, about 14:1 relative to rolling resistance (at speeds in excess of 20km/h).

Moulton identifies inflation-pressure and wheel size as factors that contribute to rolling resistance, and says that the wheel size is by far the less important of the two; inflation pressure "dominates".

What I think Moulton's saying in the video is this: coupled with suspension, the little Moulton wheels may do slightly better than a high-inflation-pressure 700c tire on wheels without suspension. There he's talking about the overall design, not about the wheels alone.

Regards
T

P.S. Nor is Dahon referring necessarily to the wheels alone when they say the Hammerhead would be edged out by a fast 700c racing bike.

fmattheus

I agree with Timo, at 3:50 he's saying that in tests his bicycle was faster than standard bikes. He's not saying that smaller wheels have lower rolling resistance. It's the combination of small wheels, high pressure and suspension that gave the bike the edge, not just the small wheels alone.

makeinu

I think I have more experience with a greater range of wheel sizes than most around here (most folks think 30% smaller than standard is small, but my 8 inch wheels are 70% smaller than standard) and have no problem believing this statement.

On smoothly paved roads the effect of wheel diameter on rolling resistance seems to be greatly exaggerated and can easily be compensated for by higher pressures. On the other hand, road imperfections seem to make high pressure tires have higher rolling resistance, so increasing pressure doesn't solve everything. Suspension can give the best of both worlds and large diameter wheels are a type of suspension. However, like itsajustme said, a dedicated suspension system is more aerodynamic than a large-wheel suspension.

jagatron

I have a hard time visually believing this (his bike tests faster than larger bike) that seeing the rider in his video bobbing around with every single pedal stroke. There's no way that this can't contribute to a significant cumulative loss of energy.

It's difficult doing an apples:apples comparison - there are not many models of high pressure tires at 16/20" in comparison to 700c.

EvilV

There is no doubt that by getting out of the saddle and hammering at the pedals the TSR30 will bob up and down a bit. I suppose that this is why in the New Series £4000 bikes, they include a device to lock out the front suspension when riders feel that they need it. However, even at 56 years old, the summer before last, I was able to maintain an average speed of 19 miles an hour for two hours without feeling totally done in. That bike was pretty quick and in the hands of a stronger rider it would have gone faster.

jur

In the Moulton flash booklet, there is more on this subject, not enough, but more nevertheless. The tests were done on dynamometers. A link to that booklet can be found in this thread.

EatMyA**

I dont see what you guys are arguing over. The smaller wheel will be faster if everything else is the same. else ordinaries would rule the speed category. We accepted that the world was indeed not flat, we can accept this too.

I don't care anyway. THANK YOU ALL FOR THIS THREAD. This is what I want. You guys are great. Thank you for exposing me to this type of bicycle. Thank you for linking the video EvilV, that did it for me.

caotropheus

We fellows of the folding world still have some room for discussions around wheel sizes. No dough a 700 C wheel is bigger than a 20" wheel, not to say a 16" wheel. Undoubtedly smaller wheels can be store and carried easier and that's the main objective of a folding bicycle. If I hijack the wheel size discussion to the MTB world now there is the 29" wheel trend that is not so different from a 26" wheel. And to spice a bit more the MTB wheel size discussion and because of historical reasons the 650 B size is gaining momento in the MTB arena. AS you can see, the difference in sizes of these three wheels is minimal and riders report wonderful improvements (psychologically, no dough!) in performance as the wheel size increases. Please what are your opinions about this MTB wheel size increase and increase in off road performance, when compared with the small wheel big wheel discussion we are having here for folding bicycles.

sqynt

What about the Greenspeed study? I'm surprised no one has cited that yet:

https://www.legslarry.beerdrinkers.co.uk/tech/GS.htm

The table lists the Comet Primo in three different diameters in the 37mm width. Assuming that the tires are made of the same material, the smaller diameter tire appears to have less rolling resistance. Although this could be just off-set by the advantage of a relatively wider width for a smaller diameter.

jur

The problem with Ian Sims' study is too small a drum was used (see bottom of that page). This was was also the case for Moulton tests (from that film clip), so the results are in doubt.

EvilV

A small wheel on a well paved road, with hard tyres may well perform slightly better than a large wheel, but if the quality of the road is rough, it will be at a disadvantage because it can not so easily roll over the bumps. For an off-road bike, the whole game is about the wheel's ability to roll over bumps, and we are talking bumps of four and five inches at times, sometimes with a vertical face. Larger wheels would obviously smooth these out for the rider and would probably roll over them with less chance of smashing the wheel. You could go at them faster and harder too without so much risk of going over the bars.

Of course, almost all folder use is on well made roads. I once ran out of decent road on a little coastal tour I was doing and came across a three mile stretch which was covered with flints about an inch and sometimes two in diameter. The sixteen inch wheeled bike was able to accommodate the surface, but slowly and painfully at about five miles an hour. An ATB would have romped across that - large soft tyres, big wheels, perfectly at home.

EvilV

I remember that you said this before once upon a time, but as long as the drum is large enough to replicate the same size tyre contact patch as a flat road would, what's the problem? Are you saying that Moulton's drum was smaller than that? Maybe it is, but my impression of the contact patch size is that with a high pressure tyre and a thin wheel, the length of the contact patch is maybe less than 1.5 cm. How large a drum would be needed to ensure that? Given that real world roads are less than perfectly smooth, maybe in practice the contact patch is dictated by minor irregularities in the road surface anyway. There are a couple of places I ride where there is a thin strip of perfect bitumen where utilities people have dug up pipes and then repaired the road, so I have a length of a couple of hundred yards of perfectly smooth surface. I really notice the luxurious quality and speed of that strip as I ride on and off it.

timo888 

You've asked Jur EvilV, and he may answer differently, but here's how I would critique Moulton's results...or our use of them.

Moulton's lab simulations are a real-world approximation, and the margin-of-error or margin-of-unreality in the approximation may be as great as or greater than the margin-of-victory of one bike over another. Paris-Dakar ain't Daytona. Itsajustme made a similar point earlier.

In a field-test with fewer and/or smaller bumps, the margin-of-difference may diminish, or with more and larger bumps it may increase. The bikes may even swap places on the winner's stand depending on the exigencies of the real road ... and on other factors such as design-induced rider fatigue.

So, when the differences in unmanned machine performance are only a few percentage points, I would shift the focus away from absolute measurements of maximum machine performance to ergonomic concerns. What happens to the rider's body when riding? Which design is optimal? That is, which does many different things very well, rather than one thing excellently and another poorly? I wonder why The Optimal receives so little attention? Is it because it's much harder to define a multi-faceted concept? And because the human system is harder to measure, there being so much variation from person to person?

Regards
T

P.S. I don't mean to imply that Moulton is neglecting ergonomic concerns. Just the opposite. His design emerged from ergonomic meditation.
P.P.S. Because there are so damned many efficiency weenies in the bicycle world, I have very few front-suspension choices for my Swift.

caotropheus

EvilV, I completely agree with your remarks. The point in the folding bicycle is that we want a compact package to carry around, that will be as small as the wheels allow. If small wheels have other advantages over big wheels in addition to compactness, we have further gains. That's what we are discussing here. Most of the folding bicycles have 406 mm wheels or smaller. Comparing to 622 mm wheels, the jump in size from ordinary road wheels to folding bicycle wheels is quite big.
On the case of a mountain bicycle the jump from a 559 mm wheel to 622 mm is not so big and I believe that the improvements in riding quality that many riders state are too small to be noticed (hence, "psychological") and are under the influence of a good marketing strategy from the companies that sell 29" ATB.

EvilV

Both Timo88 and Caotropheus are pointing out the very minor differences that some of these design differences impart to the real world equation. Since we all know that by far the biggest factor in real cycling efficiency is wind resistance at realistic speeds, we really are wringing our hands over the last percentage point of the effort we put into riding. If I was an Olympic pursuit cyclist, I might need to worry about wheels size, tyre pressure and bike weight, but I'd be an idiot and a non-medalist if I didn't pay far more attention to decreasing the wind resistance issues, like clothing, helmet fairing, shaving legs and presumably my face.

The joke is that cycling with a baggy jacket or flapping trouser legs, being an ectomorph rather than an endomorph in body type almost certainly make much more difference to the energy required to complete a journey by bicycle than any of the things we are arguing about. Also, while the weight weenies worry about an ounce here or there, some of us are riding around with twenty pounds of extra flesh upon their bodies - I know I am.

caotropheus

I know I am not...lucky little me, 52 kg !

timo888 

That's because the bar you're pressing has no weights on it.

Regards
T