Friday, January 30, 2009

What, The Wheel Size?

Hello folks,

Forget 700c fixed-wheels. The high-wheelers are the ultimate city bike; view traffic hazards from a trucker's perspective—eye to eye. It is very intimidating to them and they give your wide berth, which is a good thing, as cars don't see you at all and turn rather impulsively in front of you. The High-wheeler has a fixed-wheel drive, which is all the rage with the ladies; especially the Gothic bike-gang types we like to swoon over in our fair city.

No real brakes, of course, are a FEATURE that adds to the danger in traffic and the possibility of certain death from this, the ultimate two-wheel high wire act. It's only a matter of time before Ford tools up their old bike production line and we see one like the new-old mustang production.

On wheels noted earlier and below:

Triathletes often have bikes equipped with smaller than ATB (ATB are nominally 26x1.5-2.125 559mm ISO) 650 C (nominally 26 inch wheel 571 mm ISO) wheels. The 650 B size (demi Balloon nominally 26x1-1/2 inch 584 mm ISO) is actually an older French touring standard size that sits between the modern ATB (thorn 26 noted below) and the common 700c (622 mm ISO) road diameter. The Triathlon racing wheel noted is actually a 650c (nominally 26x1 inches 571 mm ISO) which is an old Schwinn Balloon Cruiser 26x1-3/4 nice narrowed up for race use. I hope I got this correct?

On rolling resistance that latest wisdom that some people have claimed is that wider tires have less rolling resistance. this goes against the intuitive reasoning that says that the 700x18 mm tire is faster than a 700x25. "The wider the better," some say, "and we have testing to prove it." Continental did some original testing on their equipment and found that their 700x25 tires had lower rolling resistance than their 700x23 tires a few years back. They attributed this to the larger tire having a smaller, but perpendicular, contact patch (compared to the longer, parallel contact patch of the narrower tire). Seems reasonable.

Thorn claims that their 26 inch (ATB size tires) have lower rolling resistance than larger wheels. While I have not seen this, I do not doubt this statement, but I will say that in bicycles, as in all things, this "DEPENDS." If wider is truly better, the Triathletes would certainly gravitate away from their skinny 650c x20-23 tires (nominally 26x1 inches 571 mm ISO) to the faster Schwinn Balloon Cruiser tire 26x1-3/4 (571 x47 size 571 mm ISO) and watch the records be broken! This will not happen for many reasons, chief among them it would be impossible. Between these similar diameter tires (wider tires are taller tires too!) the wider tire has so much more rolling resistance that the narrow one might have lower rolling resistance riding on the rim uninflated. I personally set a personal best in a Time Trial years ago placing second riding 23-miles on a flat front tire in a 25-mile event. Very tricky and I would have never attempted it but a fellow in New Jersey placed first or second in the national championship 8-9 months earlier doing essentially the same thing; not by choice of course.

There are so many variables: tread, tread compound, casing fabric, thread count, width of rim, air pressure, diameter, weights of various components and the biggest are the limits of testing equipment, time and budget. The old skinny tired high wheelers had very low rolling resistance. This could be as much because of the hard (high pressure before it was cool) solid tires as the large wheels compliance to irregular pavement (sort of a suspension system of the day).

The Alex Moulton small wheel bikes we sell have been tested many times on rolling resistance and always test very well ( tops in many tests) regardless of testing style even though many claimed tests for rolling resistance did not account for other variables, An older version of this bike holds the world land speed record for upright bikes and many older HPV records were set with the newer (at the time) high performance, high pressure 17 inch wheel (most Moultons use 20-inch wheels these days). The absolute world land speed records set behind automobiles on the Bonneville salt flats are over 160 mph and they have been set with 20-inch (nominal) wheels. While I don't feel that smaller 17-20-24-26 inch wheels are necessarily faster than 700c or larger wheels my experience is they are not slower either and similar setups can vary quite a bit for a number or reasons. I was recently at a gathering of small wheel bikes in Philadelphia where, after climbing nearly 400 vertical feet in a mile, I was treated to a long steep downhill in company. After a slow start down I realized a downhill race was formulating ( my specialty). A fellow on a late model Bike Friday had about a 200 foot head-start before I realized the game was on. He was loaded with a hefty belt/backpack for the weekend and was sailing. Even though I had a very unaerodynamic handlebar bag, mudguards and rear rack and small bag I not only caught but passed him going about 4 mph faster than his 43 mph top speed all the time coasting. We had similar wheels, tires (20-inch 120 psi) and overall weight. His body, luggage and bike were probably more aerodynamic than my setup. What was the variable? I suspect it was that the Moulton has a full front and rear road tuned suspension and this may have lowered the rolling resistance but who is to know.

Conclusions and Observations:

Most rolling resistance tests rely heavily on downhill coasting contests that test ease of pedaling more than actual rolling resistance. I have seen some that tested coasting UPHILL, A small wheel bike with lighter wheels and less wheel momentum will be handicapped in this test but a heavy larger wheel wheel will often have an advantage.

IS wider better?
Perhaps, but only to a point. On a very wide tire the contact patch can grow and the aerodynamic handicap increases, tire pressure generally decreases, and the weight increases, all affecting performance and test results in a negative way.

Most tests have shown conclusively that higher air pressure tires do lower rolling resistance, but a rough surface can makes this figure go the other way unless road-tuned suspension is added.

Smaller wheels are stronger, lighter, more aerodynamic (bigger advantage than most people realize, even at touring speeds) and more compact than similar performing large wheels, which has advantages for touring and transport. In the proper frame, tires from a 20-inch wheel rim can accept 28-52 mm width tires on the same rim, offering much more versatility than is typically available with 26-700c wheels and frames.

The smaller the wheels used, the more road shock is transmitted to the rider. This may raise rolling resistance and certainly will fatigue the rider. Mountain bike suspension used on the road is styled a little like landing gear on aircraft and is designed to take sudden, very hard impacts. It does increase potential comfort, but tends to absorb pedaling effort in many designs and may actually slow the bike down rolling resistance wise on rougher roads as it tends to overcompensate small bumps. A suspension system used on the road should be designed for the road and can decrease rider fatigue and lower rolling resistance, which can be very beneficial for touring.

Continental tire tests compared several tires, but results might vary with different brands as well. I have found that Continental tires feature very stiff side-walls which, on anything but the smoothest roads, seem to increase rolling resistance in my own simple tests. A flexible side-wall tire might have different results with wide verses narrow,

Few tire tests take into account road surface variation, bumpy verses smooth and grades in between. Certain low ranking tires might out-perform high ranking ones, if the surface is changed.

Disc Brakes are hard on spokes, frames and forks. Disc brakes on small wheels may or may not exacerbate this problem.

With tires, like most things bikes, I believe I can construct tests that will make winners out of almost anything and give conflicting conclusions.

Ideal Touring Wheel and Tire:

  • Tough enough to carry the loaded bike and rider
  • Large enough cross section to protect the rim.
  • High enough rim weight and spoke count for the job at hand, without being overly heavy
  • Small enough for easy transport
  • Easy to patch, boot, install and remove
  • Self-healing from cuts (this is not advertised, but varies a lot from tire to tire.)
  • Heavy enough to do the job, Light enough to accelerate easily
  • Low aerodynamic profile (Small narrow wheels are the best; choose smilie short- if not narrow if you have to choose one).
  • Long wear between replacements
  • Accepts a high enough pressure to protect the rim and offer low rolling resistance.
and for Off the beaten path add—
  • Ease of finding local replacement
  • Small enough for economical shipping or carrying (folding models are a plus, 20-inch folders are now available.)
  • Very long wear between replacements
  • Tough enough to survive minor falls while loaded.
  • Wide enough for some off road capability (may also be needed above)
Small wheel to high wheel, it's not only the size that matters. They all can work well.

I hope my experience has been of value.

Yours in Cycling,
Gilbert Anderson

North Road Bicycle Imports
P.O. Box 840
166 Courthouse Square
Yanceyville, NC 27379 USA
toll free: 800-321-5511
local: 919-828-8999

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