Folding Bikes - Average Speed: 20" vs 700c

(Let's see, where did I put that fire-retardant suit... :D)

The question of "is a folding bike faster/slower than a standard bike" occasionally crops up, as at least a few of you know. ;) Obviously there is a lot of diversity in bikes, and the only genuinely scientific method to compare would require outfitting the bikes in question with power meters, and comparing a large number of samples.

However, I have kept track of my rides for the last few years, and thought I might as well compare the average speeds of my rides. This is hardly a rigorous test, but I've done quite a few rides so there may be some merit to the comparison.

The culprits in question are a Xootr Swift, a steel cross bike, and a steel road bike.

• Rider position is about the same on all 3 bikes
• Swift had flat bars with bar-ends, cross and road have drops
• All 3 bikes use 100psi slick tires
• Swift and road are ~25 lbs, cross is 28+
• Swift has Marathon Slicks (406, 2.0" wide)
• Cross has 28c's, Road has 23c's and 25c's
• Cross has fenders and sometimes a big trunk bag
• The routes are pretty much the same, all rides are solo, and most rides are 1-2 hours long
• Edit: All rides were done with clipless pedals

What I found was: the road bike is about 4% faster than the Swift and the Cross. Edit: a blank entry threw off the cross numbers. Whoopsie... ;)

I was a little bit surprised by this. I suspected the cross was the slow, and my subjective impression was that the Swift was the same speed as the road bike.

So, given the similarities and differences, my current theory is it's the wheels and tires. The cross bike's wheels are heavier and wider than the road bike, and the tires are a little bit wider. The Swift's wheels are smaller and ought to have an aero advantage, so it's probably a tad slower due to higher rolling resistance. It could be that the tire width, rim width and spoke count mitigates some of the aero advantage too.

Either way, I could make the Swift faster by using narrower and/or higher PSI tires and/or low spoke count wheels with narrower rims, but that would incur an even greater comfort penalty than it already has. That would still be fine for short rides, but would be problematic for me around the 60 mile mark.

Anyone else have similar records to compare?

First of all, I consider what you've done here the most scientifically rigorous test (even more so than using a power meter) because you've directly measured the desired result as opposed to adjusting the numbers based on possibly flawed assumptions regarding how the power input should be related to the speed of the bicycle. Unfortunately I do not have any such records to contribute.

Second of all, to a first approximation, a 2" wide 20" diameter tire should have rolling resistance roughly equal to a 1" wide 40" diameter tire at equal pressure; So I don't think the difference could be attributed to increased rolling resistance due to diameter alone.

My theory would be that the cross is slower simply because it's heavier (thus, increasing the peak force required at the pedals and subsequently reducing the power provided) and the Swift is slower because the marathon slicks are only mediocre tires or possibly also because its wheels (with wide tires) have more rotating mass making it effectively heavier. What kind of 23c or 25c tires are you using?

Thanks for that comparison. I am pretty sure that neither tire width nor tire weight count in significantly. It is more about the tire compound (given that all your tires are slicks). And the road surface and riding style. My tests have shown that Big Apples 2.0 where 15% faster (!) than Stelvios on my commute, mostly on bicycle lane which is quite rough. Marathon Racers where in between, 10% faster than Stelvios but 5% slower than Big Apples. Big effect was that stand-and-hammer did work better on the wider tires than on the harsh and narrow ones. Also choice of pedals play a role here due to better and secure grip. On the plain Street the Stelvios are faster but not to a measurable amount (probably 3%, didn't had enough rides for precise comparison of that). All test where done on a Dahon Mu SL. I was ~2% faster on it than on my full size bike, a full suspension MTB race bike with Racing Ralph knobby tires, a bike that rides easily full speed over any obstacle on that commute (comprising a lot of curb jumps). My Mu XL Sport is slower, ~5%. I guess because of the internal hub plus the telescoing handlepost which is limiting at high speeds and powerful strokes. My average commuting speed was 24km/h in these comparisons (usually I ride a lot slower). And finally - in your case there might be some significant loss due to a loaded rack.

Anyone else have similar records to compare?



Not yet, but I am planning to make a statistical test comparing several bicycles. I have a nice 400 m bit of road with a smooth slope nearby my place and I intend to take there several bicycles to compare average descending speeds. I intend to make the test by comparing the time each bicycle takes to descend the slope without pedaling, just giving a small inicial impulse for the bicycle start moving, most probably using a ramp. The bicycles to compare are two folding 451 mm bicycles, a road bicycle and 2 mountain bicycles (one full suspension, one without any type of suspension). I will try to make as many repetitions for each bicycle as I can, and I will let you know the results...

I'm fast on whatever I ride.... :p

heavy bikes and wheels take more power to get up to speed, but they slow down slower.

I bet anyone can tell which bike will go the fastest simply by looking at them in most cases. Almost everyone will choose the road bike. Second might be split though......

heavy bikes and wheels take more power to get up to speed, but they slow down slower.

That's exactly what makes heavy bikes slower. Which is easier, to ride 38mph for 30min followed by 2 mph for 30min or to ride 20mph for 1 hour? And 34mph/18mph? And 24mph/13mph? And 18mph/10mph?

Bikes which take more power to get up to speed yet slow down slower are obviously slower overall. However, since we know the laws of physics say they can't be slower with a constant/independent power input and the laws of physics are always right the only possible conclusion is that the assumption of a constant/independent power input is wrong.


Not yet, but I am planning to make a statistical test comparing several bicycles. I have a nice 400 m bit of road with a smooth slope nearby my place and I intend to take there several bicycles to compare average descending speeds. I intend to make the test by comparing the time each bicycle takes to descend the slope without pedaling, just giving a small inicial impulse for the bicycle start moving, most probably using a ramp. The bicycles to compare are two folding 451 mm bicycles, a road bicycle and 2 mountain bicycles (one full suspension, one without any type of suspension). I will try to make as many repetitions for each bicycle as I can, and I will let you know the results...

But what if the faster bike is faster precisely because it is easier to put power in to the pedals?

If you're interested in the speed of descending while pedaling then the only rational scientific measure is speed of descending while pedaling. You can not eliminate the statistical variation of the rider, only characterize it (ie with the average, variance, and higher moments of its probability distribution).

Using roll down tests to study bicycle speed is akin to using an ordered deck to study poker and using a power meter is akin to devising a strategy after viewing the other players hands. Sure such experimental design is "more objective", but it answers the wrong questions. The very nature of the subject is inherently uncertain/random and, therefore, any genuinely scientific approach must not try to eliminate the uncertainty but instead must grab it by the horns.

Your test results seem spot on with that of an individual I read about in another forum a few months ago, who compared his Swift, and his road bike in a similar test. He found the Swift to be about 95% as fast as his road bike under the same conditions. I don't know if his Swift was "modded", but I believe the road bike was a "sport" level model, and not a "full on" racer.

Edward Wong III
Qile Duo 5 Speed 20" Folder


(Let's see, where did I put that fire-retardant suit... :D)

The question of "is a folding bike faster/slower than a standard bike" occasionally crops up, as at least a few of you know. ;) Obviously there is a lot of diversity in bikes, and the only genuinely scientific method to compare would require outfitting the bikes in question with power meters, and comparing a large number of samples.

However, I have kept track of my rides for the last few years, and thought I might as well compare the average speeds of my rides. This is hardly a rigorous test, but I've done quite a few rides so there may be some merit to the comparison.

The culprits in question are a Xootr Swift, a steel cross bike, and a steel road bike.

• Rider position is about the same on all 3 bikes
• Swift had flat bars with bar-ends, cross and road have drops
• All 3 bikes use 100psi slick tires
• Swift and road are ~25 lbs, cross is 28+
• Swift has Marathon Slicks (406, 2.0" wide)
• Cross has 28c's, Road has 23c's and 25c's
• Cross has fenders and sometimes a big trunk bag
• The routes are pretty much the same, all rides are solo, and most rides are 1-2 hours long
• Edit: All rides were done with clipless pedals

What I found was: the road bike is about 4% faster than the Swift and the Cross. Edit: a blank entry threw off the cross numbers. Whoopsie... ;)

I was a little bit surprised by this. I suspected the cross was the slow, and my subjective impression was that the Swift was the same speed as the road bike.

So, given the similarities and differences, my current theory is it's the wheels and tires. The cross bike's wheels are heavier and wider than the road bike, and the tires are a little bit wider. The Swift's wheels are smaller and ought to have an aero advantage, so it's probably a tad slower due to higher rolling resistance. It could be that the tire width, rim width and spoke count mitigates some of the aero advantage too.

Either way, I could make the Swift faster by using narrower and/or higher PSI tires and/or low spoke count wheels with narrower rims, but that would incur an even greater comfort penalty than it already has. That would still be fine for short rides, but would be problematic for me around the 60 mile mark.

Anyone else have similar records to compare?

it's the wheel size. larger wheels have lower rolling resistances.
heavier wheels take more energy to spin up, but they also don't lose their kinetic energy as fast as light wheels. it's an issue in stop in go, but once you get up to speed and maintain it, it's moot. aerodynamics play a bigger factor in constant speed.

http://www.schwalbetires.com/tech_info/rolling_resistance

heavy bikes and wheels take more power to get up to speed, but they slow down slower.

Intuitively one tend to agree. But from math/physics that is a neglectable effect. Energy in rotating wheels is almost neglectable, if you compare this to the total mass, bike + rider. Also total (bike) weight plays a secondary role for end speed, it is important for acceleration or climbing only.
But weight is important for manoeverability. And I also believe it reduces rolling resistance over imperfect roads as bike can quicker rebounce.

it's the wheel size. larger wheels have lower rolling resistances.
heavier wheels take more energy to spin up, but they also don't lose their kinetic energy as fast as light wheels. it's an issue in stop in go, but once you get up to speed and maintain it, it's moot. aerodynamics play a bigger factor in constant speed.

http://www.schwalbetires.com/tech_info/rolling_resistance

That's impossible because when you account for both width and diameter it's the Swift's wheels which are actually larger in terms of rolling resistance. According to the Schwalbe site the reason skinny tires are typically faster is because they're run at higher pressures, which isn't true in this case (100psi all around according to the OP). Moreover, as noted by Baccaigalup the smaller wheel should actually have better aerodynamics, not worse.

IMHO, it can't possibly be anything but the quality of the tires because it's the only explanation which is physically possible.


Intuitively one tend to agree. But from math/physics that is a neglectable effect. Energy in rotating wheels is almost neglectable, if you compare this to the total mass, bike + rider. Also total (bike) weight plays a secondary role for end speed, it is important for acceleration or climbing only.
But weight is important for manoeverability. And I also believe it reduces rolling resistance over imperfect roads as bike can quicker rebounce.

Wrong. If the source could generate power/energy at a constant rate regardless of outside factors then the effect would be negligible as you say, but this isn't true. In fact, oscillations in the load result in greater inefficiency within the power source which, in turn, reduce the power at the pedals for a given energy expenditure.

Unfortunately, there is no way for me to impart several degrees of higher education in a message forum, but as an excellent professor of mine often said "convince yourself" by reading about impedance_matching (http://en.wikipedia.org/wiki/Impedance_matching) and normalized power (http://home.trainingpeaks.com/articles/cycling/normalized-power-intensity-factor-training-stress-score.aspx) that the importance of acceleration and climbing is much greater than indicated by the naive assumption that power can be generated independently of the bicycle being ridden and other external factors.

Also, strictly speaking rolling resistance is increased by weight. Traction, however, is also increased which might perhaps result in a higher overall speed despite increased rolling resistance.

Swift tires: Marathon Slicks
Cross tires: Conti Grand Prix 4 Seasons
Road tires: Specialized All Condition / Conti Ultra Sport

I'm not seeing how tire compound is the primary culprit; the Slicks were made to be fast, the cross tires are race tires, and the road tires are nothing special. I'd have to weigh the wheels to actually figure out which ones are heavier.

Road surfaces vary on the ride itself, but are mostly halfway-decent asphalt and are the same from ride-to-ride.

I may try pumping the cross tires to the max (116 psi), obviously results will require a few rides.

Have you considered testing your theories on a velodrome?
It would give you a more controlled atmosphere in terms of surface quality, distance and wind effect.

My understanding is this: the deflection of the tire or the flat contact patch length is like a hill or pot hole that must be overcome by the peddling force. The larger the diameter the easier it is to get it to roll over a contact patch of the same length. All things being equal, and of course they are not, given tires of equal diameter at the same pressure, the wider tire should have less rolling resistance. That is because the contact patch area is the same but not as long. This is why fast automobiles generally have wider tires. The higher the pressure in a tire the less deflection or contact length, so high pressure tires should be faster. This neglects weight and its effect on radial acceleration or tire side issues that most wide tires have or the aero factor on the tires.

Incidentally the small deflection of train wheels on steel track is why trains are so much more efficient fuel wise.

less contact patch = lower friction. trains can go fast because they have very low rolling resistance. they really suck at stopping and going up hill however.

race cars use fat tires for more traction going around corners and accelerating, but if you look at land speed record 'cars', like the thrust SSC, they use a very narrow, high pressure tire since they aren't being driven and don't require much traction once they are up to speed.