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  1. #1
    cyclist/gearhead/cycli... moxfyre's Avatar
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    How were wheel sizes chosen?

    Why are bicycle wheels the sizes they are (besides the need for standardization)? ~27" for road bikes, ~26" for most mountain bikes, smaller for BMX.

    What's the advantage/disadvantage of a larger wheel? It seems to me that a larger wheel gives a bicycle larger gear-inches, without increasing the size of the chainrings, and provides more rotational kinetic energy to each wheel (giving it extra energy to roll over a bump or something). The disadvantage would be greater weight I suppose.

    Anybody have a good scientific answer for me?

    (Sorry, but I'm on a bicycle physics kick. I've been reading about steering geometry and this fascinating article about "trail" and its effect on stability, oh ya and this site too.)
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  2. #2
    Get outdoors! :) Becca's Avatar
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    I don't know all the science, but I have a few pieces of information for you... for one thing, a large wheel rolls easier than a small wheel. For instance, a lawn mower with small wheels pushes a little harder and has more trouble with obstacles than one with larger wheels.

    Another thing is that larger wheels turn fewer revolutions to cover the same distance as smaller ones do. If C=pi*d (C=circumference; pi approximates to 3.1415925653589 [yes, I'm a geek, I have that memorized ]; d=diameter), then a 3" wheel has a circumference of 9.424777961 inches. Likewise, a 6" wheel has a circumference of 18.849555922 inches. The 3" wheel will have to turn twice for every one revolution of the six inch wheel to cover the same distance.

    Likewise, a 700mm wheel has a circumference of 86.579325099 inches (I converted) while a 26" wheel has one of 81.681408993 inches.

    As to why these sizes were picked... I haven't a clue. Good topic for doing a Google history search, though...
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  3. #3
    Get outdoors! :) Becca's Avatar
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    Found this at http://www.bikecult.com/works/wheelsizes.html

    "Countless kinds of tires and rims have been made for bicycles. Before tire and rim standards were set by the European Tire and Rim Technical Organization (ETRTO) and adopted c.1970 by the International Standards Organization (ISO), manufacturers in different countries produced their own tire and rim sizes.

    "Most tire and rim sizes are nominal, not always the true measure, just close designations. Bead Seat Circumference (BSC), or Bead Seat Diameter (BSD), where the tire bead seats in the rim, is the most accurate measure. French Metric tires are measured by diameter in millimeters, and by width in letters (A is narrow 20mm, D is wide 50mm). An exception came with narrow 700-size clincher tires designated as C. Fractional Inches tire sizes usually fit wheels with European straight-bead rims and British wired-on rims. Decimal Inches tire sizes usually fit America hook-bead rims. Narrow width tires (18cm to 25cm or 1-1/4" to 7/8") usually fit hook-bead rims."
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  4. #4
    Senior Member sydney's Avatar
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    Quote Originally Posted by moxfyre
    Why are bicycle wheels the sizes they are (besides the need for standardization)? ~27" for road bikes, ~26" for most mountain bikes, smaller for BMX.

    What's the advantage/disadvantage of a larger wheel? It seems to me that a larger wheel gives a bicycle larger gear-inches, without increasing the size of the chainrings, and provides more rotational kinetic energy to each wheel (giving it extra energy to roll over a bump or something). The disadvantage would be greater weight I suppose.

    Anybody have a good scientific answer for me?

    (Sorry, but I'm on a bicycle physics kick. I've been reading about steering geometry and this fascinating article about "trail" and its effect on stability, oh ya and this site too.)
    Sheldon Brown has an article on wheel sizes. AFWIW, the current road standard in the US is 700c.

  5. #5
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    Historcally, the most important factor has been rolling resistance, and larger wheels have less resistance.
    The 27" (700c) size is the largest that you can fit into a frame suitable for an average sized male (and hence is too large for a small female).
    The use of 26" by MTBers is historical accident rather than analysis. The early MTBers used Cruiser style bikes with ballon tyres. French off-road tourists have traditionally used 650b, which is a similar (but different) standard.
    BMX 20" wheels were designed for small people to start with, and needed a small wheel for agility and strength.
    The issue of larger wheels giving higer gear-inches is irrelevant. Where Triathalon riders use 650c (26") wheels, they also use larger chainwheels.

  6. #6
    Ex Racer, frame builder
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    I think modern road bikes could benefit from smaller wheels.

    Historically cycle builders had to offer reasonable comfort on very rough roads. Larger wheels roll over roughness more smoothly, as the wheel starts to climb earlier and descend later.

    With highwheelers the wheel size was your gearing. In oder to go fast you needed a big wheel, and long legs to reach the pedals. Thats why tall cyclists did a lot better in races than short ones.

    The early safety bikes often had 30" even 32" wheels, before 28" became the standard for almost 80 years. 27" then 700mm are relatively recent develpments.

    I think modern racing bikes for use on smooth surfaces could benefit from say 500mm wheels, although the benefit would be so slight, that I can't see the current standard being changed.

    Bobthe....

  7. #7
    Senior Member royalflash's Avatar
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    according to studies by alex moulton 20 inch wheels are more efficient that 700c wheels in terms of rolling resistance at least but they are banned by the racing authorities

    see:

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

  8. #8
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    Bigger wheels are also harder to turn so that can take away from the rolling resistance advantage. So for a course with lots of hills and slow going, the bigger wheels would be a disadvantage.

  9. #9
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    The bicycle has evolved over many years and initially big wheels were chosen to smooth out the rough roads of that time. With today’s better roads wheels could be a little smaller but standards have been set and it is doubtful things will change.

    My namesake Alex Moulton (No relation.) inventor of the small wheel bike drastically reduced the size of the wheel but then found it necessary to add suspension to compensate for the harsher ride. Or rather it was the other way round he invented the suspension which enabled him to use smaller wheels. Either way my opinion is a road bike needs suspension like a one arm man needs a calculator watch.

    I will say the current standard 27 inch wheel, which when actually measured is closer to 26 ˝ inches; is a good size for the complete range of frame sizes. I used to build a range of frames from 48cm. to 66cm. but if I was building a bike to be the center piece of a Trade Show display or for a photo shoot I would always choose a 56, 57, or 58cm. frame; in other words the sizes right in the middle of the range, because these sizes are most pleasing aesthetically as a complete bike.

    I have a theory that if something looks right aesthetically it is probably right from a practical point of view. Bikes below these mid sizes the wheels start to look too big and for the larger sizes vice versa. From a frame builder’s prospective it would be nice to have different wheels for different size frames, but in the real world that’s not going to happen.
    Last edited by Dave Moulton; 11-13-04 at 08:34 AM. Reason: Choice of words
    History, photos and tech articles on my website. Also check "Dave's Bike Blog."

  10. #10
    Senior Member MudPie's Avatar
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    Quote Originally Posted by moxfyre
    Why are bicycle wheels the sizes they are (besides the need for standardization)? ~27" for road bikes, ~26" for most mountain bikes, smaller for BMX.



    steering geometry and this fascinating article about "trail" and its effect on stability, oh ya and this site too.)

    I'll take a more cynical approach as to why certain sizes prevail(ed).

    Like with any budding industry, there were many wheel sizes, say 100 years ago (as mentioned in previous posts). Each company had their own sizes which distinguished themselves and served as selling points. As companies faded or were bought out, their unique sizes vanished. Also, when standardizing (like with the International Standards Organization), companies try hard to make their product the "standard", so they'd have an advantage over their competitors (don't have to re-tool, engineer or change product lines...). Although ISO is a voluntary standards organization, most will comply to take advantage of standarized parts and systems.

    So I hypothesize that the standards we have today may not be the result of engineering and science, but rather, the marketing and product promotion aspects in a free economy.

    (I've written engineering standards for the American Society of Testing and Materials and it's common for the standards writing process to slow because of individual interests.)

  11. #11
    Videre non videri
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    The world's fastest bicycle had small wheels...
    http://www.canosoarus.com/08LSRbicycle/LSR%20Bike02.htm

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