How Do Small Wheels Ride? (Part 1)

This is a very important question for many people considering a folding bicycle, or the many other small wheeled options on the market, and it does raise a legitimate challenge for small wheels. Before addressing this though, I should thank Tony Hadland as much of my knowledge of this issue is drawn from his excellent articles and books. Anyway, for a given tire, pressure, load, and road surface, bigger wheels roll more easily. This is due to the fact that a larger wheel will roll over many of the small crack and crevasses in the road that a small wheel will sink into. Due to its' larger rotating mass it also rises and falls more slowly than a smaller wheel. Finally, a small wheel will contact the edge of any hole or bump at a steeper angle than a larger wheel. Envision a monster truck as compared to a regular car:
Or, if you like, check out this graphic I had Pixar whip up to demonstrate my point: Pretty convincing huh? Seriously though, it is an issue. This is actually one of the key reasons that small wheeled mountain bikes don't work particularly well.

Another issue impacting ride comfort is the fact that small wheels are inherently stiffer than larger wheels. This is great sprinting or hill climbing since you don't have to worry about your wheels flexing laterally, but not as great for general riding comfort as it means that the wheel is less compliant vertically, and thus produces a slightly harsher ride quality. (Does this bit remind you of anything you have heard in a bike magazine or shop . . . i.e. "this carbon bike is completely laterally stiff, yet wonderfully vertically compliant -- it produces the perfect ride!!!" Yeah, yeah, yeah, tube shaping and layup techniques have worked some magic in this department, but does it strike anyone else as a bit of an oxymoron to claim that a bike is stiff and compliant? Having worked in the bike industry, I can assure you that most of these claims are just marketing, so don't buy into the hype too much!) Well, enough of that digression . . .

All of the aforementioned issues combined with wood or steel rims and the most primitive of tires led to the modern approximately 28" nominal wheel size. It was the largest wheel size that could be easily accommodated in the diamond frame of the early "Safety" bicycles. However, much as the medieval carts of old have evolved into the Mini Cooper of today . . .


. . . modern technology can adapt to these issues and produce excellent ride quality in a folding/small wheeled bicycle. How? Find out next time, as for now, get up and go ride.

Small Wheels are Slower, Right?

Hey, loyal readers! Sorry to disappoint all six of you with the 4 day layoff, but it was a busy weekend of . . . well, nothing. Stuff went down, etc. . . in the future you can expect at least 3 posts a week, sometimes as many as 5 though, so . . . you got that going for you. Anyway, on to the question of the day: Are Small Wheels Slower? This presumption is a common misconception, with some basis in fact, but probably not for the reasons many would expect. The most common point was addressed last time -- different gearing ratios allow small wheels to propel you at the same speed as larger wheels. Beyond this issue, we have to flip back to the physics that govern how a wheel functions. (Before delving into this I'd like to thank Bike Friday, Alex Moulton, and Tony Hadland for contributing to my own knowledge of these issues. I'll summarize what I gleaned from them in this post.)

I'll kick off with some of the more easily understood advantages. 1) Smaller wheels weigh less; 2) they present a smaller frontal area, and thus less aerodynamic drag; 3) the shorter spokes also produce less turbulence as they rotate -- turbulence equates to aerodynamic drag, thus smaller wheel are doubly better in this case. (You can even use disc wheels or some sort of cover for the spokes to further alleviate this issue as in a time trial bike with a much lower destabilizing effect from crosswind)


Ok, so those 3 points are pretty easy to grasp; the next issue relates to inertia and involves both positives and negatives for small wheeled bicycles. When you accelerate from a stop on a bicycle, the vast majority of your energy goes towards putting the mass of your body and your bicycle into forward motion. In the case of the wheels, you are not just moving their mass in the direction you are traveling, but setting the whole mass spinning as well. The lower overall mass of small wheels means this is an easier task, but you also benefit from the fact that the mass is closer to the axle of the wheel.

Imagine opening a door. Normally, the knob is placed far away from the hinges (the fulcrum) and it requires relatively little force to open. Now imagine closing the same door, but instead of pushing near the knob, you apply force very close to the hinge . . . it will be incredibly difficult. The same concept applies to bicycle wheels -- a case in which you are always driving forward momentum by applying a force near the fulcrum point (the rear hub). Thus the larger the wheel, and consequently the further away the rim and tire are from the center of the hub, the more force you will have to impart to start the wheel rotating. (I think that may have been the most simplified explanation of torque and the physics of levers and wheels in all of human history; for a more detailed discussion go here, or here, or check out this book.) The end result of all of this is that is is easier to accelerate a bicycle with smaller wheels. This by the way is not just a hypothetical difference, it is noticeably easier. The converse though is that at speed, you have a smaller flywheel effect from the mass of the wheels tendency to remain rotating. This means that after speeding down a hill on your small wheeled bike, you will experience a little less momentum carrying you up the next hill. I cannot say I have personally noticed this to the same extent I notice quicker acceleration at low speeds, but science says that it is there.

I am sure you as you read all this, you are thinking "That physics stuff is great, and I conceptually understand these effects, but what concrete numbers can I apply to actually riding?" Thankfully someone else wondered the same thing and the end result is that the smaller rotating mass of small wheels is more efficient below 16 mph, and the greater gyroscopic effect of a larger wheel is beneficial above 33mph; between the two speeds the difference is minimal. I am sure that we all think of ourselves as speed demons, but how often do you really go above 33 mph? Not that often right? (If you disagree, then you are deluded -- the record speed in an individual time trial in the Tour de France is a 34.27 mph average over a 4.47 mile course). So in the case of normal riding, small wheels will either benefit you or be no different from regular wheels speed wise. If you live in a city and commute like my self, smaller wheels are especially nice because you are constantly stopping and starting with the flow of traffic.

If you are still skeptical, keep in mind that virtually all human powered vehicle speed records are set with small wheels. Check out the International Human Powered Vehicle Association (IHPVA) for further info.

Varna Diablo II - the fastest human powered vehicle on earth at 81 mph

Moulton Liner II - The fastest upright bicycle in the world since 1986 (51.29 mph)

All in all, I think that should answer any doubts about the speed of small wheels. Next time we look at the ride quality / comfort of small wheels and folding bikes. As for now, get up and go ride.

Don't I Have to Pedal More?

For many people, this is the very first question they will ask when encountering a small wheeled folding bicycle. (I will discuss folding bicycles with normal wheels in the future) I have heard this query more times than I can count, and it is often followed by " . . . really? . . . like you can go up hills and everything?!?" -- and I can assure you that yes, I can go up hills with my folding bicycle. in fact, I can bike at the same speed as a normal bicycle in any situation.

This miracle is brought to you through the amazing simple machine that is gearing. So, if you have smaller wheels, you can compensate by either using larger chainrings, or smaller cogs on the cassette / freewheel / hub gear. Shimano even makes a group specifically for this purpose called Capreo, and despite the need for some new tools to install and remove (a completely uncommon issue in the bike industry), it works really well. In general though, special equipment is entirely unnecessary because most of us bike in the middle range of our bicycle's gearing most of the time. Smaller wheels and standard gearing just mean that you use a higher gear that you normally would to ride at a given speed. Sure you lose that 110 inch top gear, but you may gain some nice lower end gearing to plod up hills (especially nice for commuting). For you roadies out there, this is basically the same concept as a compact crankset, which as you may have noticed is all the rage these days. In all reality, a small percentage of bicycle riders need or even use the highest few gearing combinations they have (53-11 much?). Given this fact, you would be much better served by a lower range with narrower jumps between gears. In fact this will even offer greater efficiency as you have more gears to chose from while riding the speeds you normally ride at, and it also encourages you to ride smoothly at a higher cadence in a lower gear as opposed to stomping on the pedals and wasting energy.

So, to answer the question, no, you don't have to pedal more with smaller wheels. You may not have the same high end gearing available to you as on a traditional road bike, but you can if it is that important to you! However, when you actually take the time to think through how you bike and what you want to use your bike for, I think you may realize that the lower gearing easily offered on a folding bike with standard parts will be a more functional set up. Many of the benefits of folding bicycles come down to this point of functionality; and as with many aspects of life, functional utility is the most important factor driving long term usage and enjoyment of a product.

Sure that Colnago Presidente looks AWESOME hanging in the bike store's window. Fortunately, it will also look awesome hanging on your wall when you try to pass it off as an artistic tribute to modern industrial design while explaining why you don't ride it 6 months after purchase.

Tune in next time for "Aren't Small Wheels Slower?", as for now, get up and go ride.