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Thread: Wheel diameter?

  1. #1
    eternalvoyage
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    Wheel diameter?

    Rolf at Hostel Shoppe said that larger diameter wheels allow recumbent riders to keep up, when riding with a group of fast road bikes. He said that the smaller wheel diameters (below 26"/559mm) are slower, and that riders were slowed down enough by them to make a noticeable difference.

    But I have also heard conflicting reports. The world-record-holding bikes for speed (when drafting behind a lead vehicle) use smaller diameter wheels. Also, Alex Moulton has talked about his decision to use smaller-diameter wheels, and about their greater efficiencies, and about the fact that trains, airplanes, and cars all went from larger to smaller wheels as they evolved.

    So, what I'm wondering is if anyone here has anything to add that will help clarify this.

    (Between 700c, 650B, 650C, and 26" (559mm), there seems to be very little difference. When you drop down to 20", though (406mm), some people claim a significant difference....)

  2. #2
    Senior Member BlazingPedals's Avatar
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    This is just me talking, so ignore as necessary.

    I'm a big wheel chauvinist. I believe the efficiency of large wheels is greater than small wheels. Large wheels don't have to turn as fast at a given speed as small wheels, so there are smaller losses to bearing friction. Larger wheels will roll over surface imperfections better. In a drive situation, they offer greater gear range when using standard parts than a small wheel does. Finally, larger wheels have more choices of good, low rolling resistance tires. There are a few good ones for 559 and smaller, but even the best of them would not be considered standouts in the 700c world.

    Small wheels make sense when the packaging requires them, such as in streamliners or front wheels on many bents, or even on folding bikes. But I don't believe they're the best choice for speed.

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    All of the things wrong with small wheels are insignificant in the modern world except one: wide range gearing is difficult to achieve. Impossible actually without geared hubs or cranks or intermediate gears. Ride quality issues can be addressed with suspension. Does one really need dozens of tire choices? An adequate selection of quality and pressure (psi) levels exist in 20" wheels.

    H

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    Quote Originally Posted by Leisesturm
    Ride quality issues can be addressed with suspension.
    Perhaps, but suspension is expensive and adds significant weight.

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    cyclopath vik's Avatar
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    Except on a perfectly smooth race track or freshly paved road smaller wheels will be slower.

    However, your other point about keeping up with fast DF road bikes will really depend on your recumbent's weight and how well you can climb on it. I climb faster on my DF road bike than any bent I have owned. If I was racing myself I'd drop the recumbent me on the climbs and I would not lose enough time on the flats/descent to make up for that. If we are talking a group of DF road bikes in a paceline that would be doubly true.

    If you want to stick with fast DF bikes get a light recumbent with big wheels and make sure you are able to climb well with it. If you can get ahead of the flats do it so you have a bit of a cushion for the next climb. The problem with this is that you end up not riding with the DF bikes very much which might be what you are after. It is just hard since the two types of bikes have different strengths & weaknesses.
    safe riding - Vik
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    Senior Member BlazingPedals's Avatar
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    I wish I knew where it was, but I once saw a rolling resistance chart that showed a 20" Stelvio, which is about the lowest rolling resistance tire you can get for 20", at about 28 watts. OTOH, there were quite a few everyday 700c choices down around 23 watts. So those fragile 20" racing tires are almost 20% worse than what many roadies routinely use. It's true that it doesn't matter how many choices there are if one of the choices happens to be something you'd be using anyway, but unfortunately I've had terrible luck with both Stelvios and Contis, and the list of available 20" tires beyond those start seeing big increases in rolling resistances.

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    Cycling Anarchist Trsnrtr's Avatar
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    While I agree that big wheels roll well and feel better on rough pavement, my fastest sustained averages (greater than two hours) have been on two bikes with 20" front wheels. I also have owned two twin 650C bikes. I guess the total package means more to me than just wheel sizes.
    Dennis T

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    This is a favorite bent discussion and we all have opinion, born of experience with our local roads.

    Before I turned my RS24 into the low geared touring trike it ran at the same speed as my Windcheetah, 24" vs 26" drives respectively. And the fronts on the RS are 20" vs 16" Moultons on the Cheetah. And the tires on the RS are all fatter.

    It could be fashion that DF's all run 700's, could just be being different that some MTB have gone up to 28", but why did RANS alter the Stratus with the big front wheel, or the ever "Speedy" Rotator Pursuit with the dual 700's if the small 20's were as fast. After all. we are told that the 20" offer less wind resistance than the big wheels, and at speed aero is more important than weight, oh, and the small wheels are lighter with the added benefit of being stronger.

    I can watch the speed drop when one road turns from smooth to chipseal, the drop is about twice as much with a small, high pressure wheel vs the DF. Bad pavement, poor patching job and potholes suck even more speed off.

    Two of the three cases of road rash I've had have been on machines where one or more wheels were sub 26 dealing poorly with ruts that didn't bother big wheels, the third was car/bike interaction. So, IMO small wheels are less safe in ragged pavement, which I have a lot of around here, Of course, there were other factors involved in the crashes, but for the sake of this discussion, let's just blame the 16" wheels.

    For myself, it is all fashion, I like the looks of a large drive wheel and a smaller lead. The Cheetah looks fast, the trikes with the same size wheels look odd to me. If I were to go back to riding two wheel bents it would be another Stratus, 26/20, not another high wheel racer. It is looks,,,,

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    The last poster had me sucked in behind for the ride until s/he mentioned 'looks'. I was never trying to argue that small wheels don't drastically decrease the ride quality when the going gets rough. Suspension must be used and it better be well designed too. Moulton knows that and from the very beginning his 20" bikes were suspended even though suspension science has come a long way since his first efforts. Smaller wheels are stronger wheels period. However, at the present level of performance even large wheels are not in any danger of failing in normal use. Still, at the present state of the art of recumbent design, when a rear wheel is driven it must be 26" or larger in order to use a long cage derailleur. When the driven rear wheel is 20" some kind of expensive geared hub or jackshaft intermediate must be used to get a decent range or high gear.

    H

  10. #10
    cyclopath vik's Avatar
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    Quote Originally Posted by Leisesturm
    The last poster had me sucked in behind for the ride until s/he mentioned 'looks'. I was never trying to argue that small wheels don't drastically decrease the ride quality when the going gets rough. Suspension must be used and it better be well designed too. Moulton knows that and from the very beginning his 20" bikes were suspended even though suspension science has come a long way since his first efforts. Smaller wheels are stronger wheels period. However, at the present level of performance even large wheels are not in any danger of failing in normal use. Still, at the present state of the art of recumbent design, when a rear wheel is driven it must be 26" or larger in order to use a long cage derailleur. When the driven rear wheel is 20" some kind of expensive geared hub or jackshaft intermediate must be used to get a decent range or high gear. H
    The trouble with suspension is that it adds weight and that will negatively affect climbing speed which is the bane of bents. Hills are where the roadies will smoke you every time and the only way to fight back is train on hills + use a light bent.

    Quote Originally Posted by Trsnrtr
    While I agree that big wheels roll well and feel better on rough pavement, my fastest sustained averages (greater than two hours) have been on two bikes with 20" front wheels. I also have owned two twin 650C bikes. I guess the total package means more to me than just wheel sizes.
    Agreed - it is the total package that counts. My Volae Expedition with dual 26" wheels is going to be slower on a mixed course than a Fujin SL2 which has that small 20" front wheel simply because the Fujin is so much lighter and very aero. But, give me a highracer with dual 650C wheels that weighs the same as the Fujin and I would wager it will be faster on the road. On a smooth racetrack I'd bet on the Fujin.
    safe riding - Vik
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    Quote Originally Posted by vik
    The trouble with suspension is that it adds weight and that will negatively affect climbing speed which is the bane of bents.
    Not just bents, anything. The whole bents don't climb as well... etc. is being debated right now in the next thread. The 'only' reason upright bikes can outclimb bents is because the rider can stand and use his weight but if the hill is long enough and he has to sit and spin it out then he won't have any more advantage than 'maybe' that his DF will weigh less than the bent he is trying to beat. But since more and more DF bikes have suspension and not only on small wheels but 26" wheels too, it is futile to aruge against it. Suspension is here to stay. It will get smaller, lighter, better, as will disc brakes. There will be very little difference between a decent HPV of any design and powered bike or full on motorcycle. The needs of a 'vehicle' be it bicycle or velomobile, motorcycle or automobile are the same. The only reason suspension, disc brakes, geared hubs, etc. have been slow to enter our market is the usual one. Money.

    Quote Originally Posted by vik
    Hills are where the roadies will smoke you every time and the only way to fight back is train on hills + use a light bent.
    Hills are where a fitter rider will smoke you regardless of what you are riding. The only way to fight back is to become fitter than the rider you want to beat. What does a Windcheetah cost? A lot I am sure. It is one light bent isn't it, but I suspect AWD or whoever it is makes them would sell tons more if they were 1/3 the price like, say, an Actionbent. Roadies have the same dilemma. How many roadies can afford <10lb carbon fiber DF's? They would be even faster up the hills than they are now on the 25lb iron they presently ride.

    H

  12. #12
    cyclopath vik's Avatar
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    Quote Originally Posted by Leisesturm
    Not just bents, anything. The whole bents don't climb as well... etc. is being debated right now in the next thread. The 'only' reason upright bikes can outclimb bents is because the rider can stand and use his weight but if the hill is long enough and he has to sit and spin it out then he won't have any more advantage than 'maybe' that his DF will weigh less than the bent he is trying to beat. But since more and more DF bikes have suspension and not only on small wheels but 26" wheels too, it is futile to aruge against it. Suspension is here to stay. It will get smaller, lighter, better, as will disc brakes. There will be very little difference between a decent HPV of any design and powered bike or full on motorcycle. The needs of a 'vehicle' be it bicycle or velomobile, motorcycle or automobile are the same. The only reason suspension, disc brakes, geared hubs, etc. have been slow to enter our market is the usual one. Money.



    Hills are where a fitter rider will smoke you regardless of what you are riding. The only way to fight back is to become fitter than the rider you want to beat. What does a Windcheetah cost? A lot I am sure. It is one light bent isn't it, but I suspect AWD or whoever it is makes them would sell tons more if they were 1/3 the price like, say, an Actionbent. Roadies have the same dilemma. How many roadies can afford <10lb carbon fiber DF's? They would be even faster up the hills than they are now on the 25lb iron they presently ride.

    H
    Well my experience disagrees with you. I would be faster on my DF touring bike than my dual 26" highracer - similar weight bikes, on long mountain passes as well as shorter climbs. I tend to stay seated when I climb and I can generate way more power on my DF bike than my bent while climbing.

    I have been "beaten" uphills on my bent by riders on a DF bike that I would smoke on my DF touring bike. Obviously fitness matters, but the reality is I have not heard of many people who can climb as fast on a bent as on their DF bikes.

    My experience is only one data point however.
    safe riding - Vik
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    Leisesturm wrote:

    "The last poster had me sucked in behind for the ride until s/he mentioned 'looks'."

    thanks, I guess you got my point. My collection has been Linear, Stratus, bikeE, EZ1 and Corsa, two different Catrikes, including a Speed, currently a Cheetah and RS24, oh and a couple of tandems too. I would have had a Bachetta Aero (is my memory failing me yet again, their fastest, Ti job) except I am too big, 6'4", 200# and the Bachetta boys didn't think their machine would hold up, so I got the steel Corsa.

    Aerodynamics is more important than wheel size for speed, the trikes are faster than any of the two wheelers I owned, except the Corsa, because they are all inefficient, upright riding positions, catching lots of wind. The Cheetah is faster than the RS because it is more laid back, same enigine, same road 26 on the Cheetah, 23 on the RS. I would guess i was fastest on the Stratus going up long grades, 6% for a mile or more, because its position suited me better, but i had to upgrade the wheels/hubs to get it there.

    Climbing is all about power to weight, speed is, at some point all about aerodynamics, never about wheel size. Until suspension is more developed, ie lighter and more responsive, I'll take a wider, lower pressure tire to solve the ragged road problems.

    a small diversion...

    I was very pleased with the Speeddrive on the 20" drive Catrike Speed, I have never liked the convoluted three speed hub with seven gear ala Greenspeed. i've yet to try the Roloff that is supposed to be woderful solution to the small drive wheel dilemma. 26 works great, and because of my size, I appreciate the long wheelbase that it brings along with it.

    And why doesn't anyone want to take my bait about small wheels causing my crashes....

    Mike

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    A bike with a 20" rear wheel can keep up with DF bikes - as long as it has the gearing to make up for it. Usually this means the bike will have a massive 63 tooth chainring up front, and low-toothcount cassette in the rear.

    That said, I must admit that I'm a big rear wheel advocate myself. I know, from owning a trike, that the large rear wheel rolls over cracks with less shock transmitted to the rider than the smaller front wheels. There's also a larger selection of tires for larger wheels than for small ones.
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