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Tech Factors for Smoother Rides on Small Wheel Bikes

GrantT

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Only then was I allowed to test ride the D9 again, and from which ride I instantly concluded that the bits on the P10 were way better. But again, and with reference to the OP, I’m clueless about why that should be. Derailleur tech is at least 100 years old; shouldn’t we be able to pick up cheap group-sets at Daiso by now?

That's about what the bike maker did for the D9, or at least the wholesaler equivalent of a Daiso. Anyway, it may have felt clunky but it's Shimano so should last okay.
 

joewein

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The P10 uses a 10 speed Deore rear derailleur vs. the 9 speed Acera on the D9. Shimano changed the parallelogram on mountain derailleurs such as the Deore when going to 10 speed. The 10 and 11 speed MTB RD pull more cable for the same amount of lateral movement. They made a similar change on road RDs when going to 11 speed (as well as on the 10-speed Tiagra 4700 road derailleur), for the same reason: More cable pull allows for more precise shifting, especially when the cogs at the rear are packed more tightly because you have more of them. With the new parallelogram designs the cable pull per click is now back to around where it was in 7-8 speed days.

It would be possible to upgrade later. Cassettes wear out. If you need a new cassette and chain, going up to 10 speed would involve only a new rear derailleur and the matching shifter on top of that.

In terms of gearing range, both models have the same top gear (52-11) and similar spacing throughout the range, but the P10 adds one lower gear below the lowest gear of the D9. This shouldn't really matter around the city or on the river bike paths, but up in the mountains lower gears will be very welcome. The lowest gears are similar to what you would get on a 700C with a 10-speed 11-28 or 11-speed 11-32 cassette, respectively. For me, even the P10 wouldn't be low geared enough for the mountains - 1X doesn't have the overall range I would need.
 

joewein

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One small difference between the two bikes is not only the brand of tire but also the width: Though both use the same 451 mm bead seat diameter 20" (same rims will work), the P10 comes with 20 x 1 1/8" tires while the D9 rides on 20 x 1 3/8". The latter are a few mm wider. As already mentioned by others, the Schwalbe on the P10 is a nicer tire than the CST on the D9.

Tires are easy to replace and they change how the bike rides. The more puncture protection you add to a tire, the stiffer and more energy-absorbing the tire will become. A narrower tire needs to be inflated to higher pressures to carry the same weight with the same amount of tire deformation. That's especially true with the risk of snakebite punctures in mind, as the rim will ride a little bit closer to the road.

For that reason I would recommend a supple 451 tire but in 20 x 1 3/8 (the wider format), whichever of the two bikes you start from. I have a Bike Friday Pocket Rocket which came with 20 x 1 1/8, but I switched to 20 x 1 3/8 later and didn't look back. The difference in ride quality is quite noticeable. The wider tire run at a slightly lower pressure may initially be perceived as slower because it transmits less road buzz, which we tend to associate with higher speed, but it isn't.

A few things on the D9 look like it was built to a tight budget. For example, some of the weight difference to the P10 is likely to come from the steel fork vs. the aluminium fork of the P10. But not only is this a steel fork, it's "high tensile" steel, which despite the fancy sounding name is a pretty basic kind of steel. It is not the stronger "cro-moly" steel (also known as "4130") that classic road bikes and current touring bikes are made of. Weaker steel means thicker (heavier) tubing to get the same structural results. As a rule of thumb, hi tensile parts will be at least about 50% heavier than equivalent strength cro-moly parts because you need that much more material. Yes, we're talking cheap mamachari kind of stuff!
 
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Slowburner

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Sep 27, 2019
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These are great replies, thank you @joewein Yes, I’m interested in the difference between expectations and perceptions, and the actual contributions that various bike components make to both the experience of smoothness and the efficiency of the ride. Can I restate your points as:
1a) that running the tyre at somewhat lower pressure will will help the bike go faster, because (as I understand your arguments) it provides extra resilience, which presumably absorbs major and minor road surface imperfections that would otherwise be slowing the bike down; and
b) is that why, although we think we’re going faster when the ride is harsher but we're not (because smoother is faster); and
c) is all of that why ‘stiffness’ in the tyre is a bad thing, as you say?

2) Is it also true that these things are more relevant on small wheel bikes, because they make more contribution to smoother, faster riding (because smaller wheels are more hindered by surface imperfections, tending to ride more harshly, which actually means more slowly)?
 
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Cactaur

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Smaller wheels are slower due to circumference. You go further therefore faster on the same effort on normal wheels.

Previous thinking was to have as thin as possible tires with as much pressure as possible to reduce rolling and air resistance. This has been abandoned.

Yes if you are smoother without bouncing around it’s faster. Running less pressure with fatter tires is more comfortable, so less fatigue and contributes to speed. There is of course diminishing returns at some point.

Supple tires grip the road better and is desirable when cornering.
 
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Slowburner

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Sep 27, 2019
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One of the considerations of tyres and rims I've seen most frequently mentioned is that whilst 451 rims ought to roll a little smoother and a little faster as @Cactaur says above. Although using 20"/406 rims apparently give access to a wider range of tyres than 451 rims.

Myself, that doesn't seem terribly important if you're not getting punctures every day, and have at least one extra tyre of the sort you've chosen. However, with respect to @joewein's points about tyres, it could be more relevant, and there's plenty of 406-based folding bikes to choose from, including the Dahon P8 Lockjaw I mentioned previously.

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joewein

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Smaller wheels are slower due to circumference. You go further therefore faster on the same effort on normal wheels.

That's a commonly held misconception. Because of the smaller leverage of a smaller wheel you can drive it in a heavier gear (spinning the cassette and wheel faster) so that what you feel at the pedals for the same amount of air resistance or gradient at a given speed is the same. Smaller wheels would be slower only if they were to spin at the same number of revolutions per minute as bigger wheels, which they won't since we have gears.

It was all different back when the pedals directly drove the wheel. Then driving wheels were extra large for precisely this reason:



Notice how modern 700C wheels are considerably smaller than those wheels were then?

With a crank connected by a driving chain to a cog or cassette at the rear, pedal RPMs and wheel RPMs are no longer identical (unless you happen to chose so). So for example, you might be pedaling at a 75 rpm cadence and your crank will be a 50T. With a 700C wheel you may be driving a 16T cog on the cassette while with a 20" 451 it might be a 12T instead, spinning the wheel at 33% more RPMs instead of spinning a wheel that is 33% larger. The outcome in meters per road per second is pretty similar (8.2 m/s in this example).

Assuming sufficient gear range, the limiting factor for speed will almost exclusively be air resistance, the bulk of which will be from your body and not the bike (wheels or frame). If you compare a single speed 20" shopping bike with a 22-speed 700C road bike then yes, most likely you won't have the gears on the shopping bike to keep up with the road bike, but not directly because of the wheel size but because of the limited gearing. My Bike Friday has a gear range of 21-95 gear inches. My 650B Elephant NFE has 21 to 100 gear inches, almost no difference despite the former having wheels 3/4 the size of the latter.
 

Cactaur

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I'm thinking in terms of keeping all variables the same except for wheel size.
Lets have a relatively easy to calc gear 40x20. Same gearing, same effort diff wheel. 1 crank = 2 turns of the wheel. Bigger wheel has the longer roll out.

I'm probably missing out on the math for the difference in leverage and force needed by a larger wheel but thats above my physics level. Clearly a penny farthing is harder to crank over than a 34x34 climbing gear even if they're both 1:1.
 

joewein

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Oct 25, 2011
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These are great replies, thank you @joewein Yes, I’m interested in the difference between expectations and perceptions, and the actual contributions that various bike components make to both the experience of smoothness and the efficiency of the ride. Can I restate your points as:
1a) that running the tyre at somewhat lower pressure will will help the bike go faster, because (as I understand your arguments) it provides extra resilience, which presumably absorbs major and minor road surface imperfections that would otherwise be slowing the bike down; and
b) is that why, although we think we’re going faster when the ride is harsher but we're not (because smoother is faster); and
c) is all of that why ‘stiffness’ in the tyre is a bad thing, as you say?

2) Is it also true that these things are more relevant on small wheel bikes, because they make more contribution to smoother, faster riding (because smaller wheels are more hindered by surface imperfections, tending to ride more harshly, which actually means more slowly)?

The pneumatic tire as invented by Dunlop uses air as a suspension. Previously tires were made of solid rubber or wheels were solid wood or clad in an iron hoop, like on ox carts. Air is a very efficient medium for suspending the weight of the bike and rider, as not much energy is lost that way when it rolls, even as it goes over bumps. As the wheel spins, the contact patch moves around and some air is displaced as the tire is deformed, but air flows relatively easily.

More energy is lost when solid objects are deformed, such as the sidewalls or the tread of the tire itself. The stiffer the materials used, the more internal friction there is, which turns motion into heat. A supple tire has less of this internal friction so it doesn't matter much at what pressure you run it, the efficiency of the tire won't change much. A very stiff tire however will consume more energy when it deforms more because it won't just be the air pressure but also the sidewalls that carry weight.

With any tire, lower pressure means that less vibration will be passed into the body of the cyclist. Just as the stiff tire loses energy when it deforms, so does the body tissue of the cyclist being rattled about. So lower pressure, particularly on wider tires that have a wider contact patch, makes more sense with supple tires as it reduces energy loss inside the rider without giving up efficiency within the tire.

Yes, I would agree that rougher roads make more difference on smaller wheels, especially small narrow wheels. In some ways 406 mm, the other common tire size known as "20 inch" (and used by BMX bikes) is a better choice than 451 even though the latter has a "faster" image, simply because there is a much wider choice of tire widths for 406. You can get 406 tires up to 50 mm wide, with considerably more air volume, that are better at dealing with bad road surfaces. 451 will be faster on perfect roads only.
 

joewein

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I'm thinking in terms of keeping all variables the same except for wheel size.
Lets have a relatively easy to calc gear 40x20. Same gearing, same effort diff wheel. 1 crank = 2 turns of the wheel. Bigger wheel has the longer distance.

I'm probably missing out on the math for the difference in leverage and force needed by a larger wheel but thats above my physics level.

Yes, you're missing out on the difference in leverage of the rear wheel.

Imagine your are holding a 2 m pole with a weight at the end. Then imagine the same weight at the end of a 4 m pole. It becomes twice the effort. Well, that pole is your bicycle spokes!

If two bikes climb an equally steep hill, say 5%, and the bikes and rider weigh the same and they both use the same gearing, say 40x20 as you suggest, then the total gearing will be determined by all the levers, which are

1) the crank arm length (e.g. 170 mm),
2) the chain ring diameter or tooth count,
3) the rear cog diameter or tooth count and
4) the wheel diameter.

If 1-3 are kept equal, how hard you will have to push the pedals will be proportional to 4) i.e. the bigger the wheel, the harder a given gear ratio will feel at the pedals. So in the real world, you would chose a smaller front:rear ratio (lighter gear) with the bigger wheel and a larger front:rear ratio (heavier gear) with the smaller wheel.

The bottom line is, gearing makes up for bicycle wheels of different sizes. As long as you have the right gears, your feet will not know what size of wheels they're driving. But it's easier to build a bike with super low (light) gears with small wheels and a bike with super high (heavy) gears with bigger wheels.
 

kiwisimon

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I'm thinking in terms of keeping all variables the same except for wheel size.
Lets have a relatively easy to calc gear 40x20. Same gearing, same effort diff wheel. 1 crank = 2 turns of the wheel. Bigger wheel has the longer distance.

I'm probably missing out on the math for the difference in leverage and force needed by a larger wheel but thats above my physics level. Clearly a penny farthing is harder to crank over than a 34x34 climbing gear even if they're 1:1.
it's not the same gearing. You will have to expend a lot more energy from your legs to get the bigger tyres to spin at the same speed(RPM) as the small tyres. But I like your logic. I thought it made sense too once.
edit: What Joe said.
 
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Slowburner

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... hang on.

Leaving aside the ‘same effort for greater rotation’ argument (which never made sense to me anyway and I’m pleased to read the explanation of gearing, thank you) I always accepted that larger wheels would go faster, and believed that 451s would offer a (very slightly) higher top speed than 406s, as indicated in my earlier replies, because .... er, skateboards.

If you’re freewheeling downhill, won’t a larger wheeled bike (let’s say with the same quality bearings and the same tyres) run faster than the smaller wheeled bike like larger wheeled skateboards do?

Common wheel sizes for downhill boards are 65mm and 75mm, which is quite a bit larger than standard freestyle/street/park wheels. Larger wheels certainly appear to give a higher top speed than smaller ones, and larger wheeled boards can be seen visibly pulling away from smaller wheeled boards them as speed rises, regardless of bearings (which are very important).

That’s what I’ve observed, and what we’ve all accepted without question. And that’s what I thought was happening with larger wheeled bikes - they can carry more speed. Is that somehow incorrect then, and if it’s not, why isn’t it true for bike wheels too?
 
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kiwisimon

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Skateboard wheels assuming the same durometer and width : Rolling Resistance.
A larger wheel, with a smaller arc angle given a specific distance, will collide with fewer imperfections on the ground. Think of a pothole: if the wheel going over it is smaller than it, it will fall in trying to move over it, cause a huge thud, and lose energy climbing the other side. If the wheel is much larger than it, though, it will experience little resistance as it moves over it. Small and large imperfections work the same way, so with a larger wheel, the resistance from ground imperfections goes down and effort to maintain velocity is thereby reduced (or, if you prefer, “it goes faster”). Source: Jeff Meden https://www.quora.com/Why-do-bigger-wheels-roll-faster-What-is-the-physics-behind-this (scroll down to get a little about bicycles).

If all your riding is downhill or bumpy off road a larger diameter wheel makes sense in being "faster". 29er bikes became very popular off road for this reason.
 

jdd

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...My 650B Elephant NFE has 21 to 100 gear inches, ...

The lowest gear inches for the three models mentioned in OP are 30", 26", and 24" (click on the links there and then go to specs, and IIRC, highs are 90-something to just over 100).

While I'd agree that tires and wheel size, crank length and so on do affect 'feel', combining various details/sizes/measurements in a gear-inch calculator at least isolates the physics of it all from a rider's perceptions.
 

microcord

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Aug 28, 2012
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Is it practical to swap out bearings in wheels and cranks too, or is that sort of thing not possible until you get into higher cost bikes; is it a feature of higher cost bikes that they support interchangeable components where cheaper ones do not?

Riders determined to throw money around will want ceramic bearings. Before joining them, see this video of Hambini's: .
(Actually just about any video of his is a pleasant and educational way to pass your time, but skip the one he did about bearings on GCN because on that one it's hard to see what he's talking about.)
 

joewein

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Common wheel sizes for downhill boards are 65mm and 75mm, which is quite a bit larger than standard freestyle/street/park wheels. Larger wheels certainly appear to give a higher top speed than smaller ones, and larger wheeled boards can be seen visibly pulling away from smaller wheeled boards them as speed rises, regardless of bearings (which are very important)

Skateboard wheels aren't using pneumatic tires but relatively hard plastic wheels, usually made of solid polyurethane. That makes for quite a different ride compared to modern bicycles. Yes, those bigger hard wheels will roll faster on rough concrete or asphalt, just like in the days of the high wheeler bikes, because they will be deflected less as they roll over irregularities. Penny-farthing bikes in the 1870s/80s used huge front wheels not only because they had no gearing and wanted to make the most of every pedal turn, but also because they had hard wheels instead of pneumatic tires. It was the best way to deal with rough roads given that constraint.

With pneumatic tires the tire deformation mitigates the irregularities and much reduces their impact, even if it never completely eliminates it. However, as you go to larger and larger wheels, you add weight and air resistance, which at some point becomes counter-productive.

With skateboards there are also different trade-offs regarding manoeuvrability for doing tricks at relatively low speeds, which I understand smaller wheels will do better at, but I am really no skateboard expert (I have a son and two brothers who used to skateboard).
 

joewein

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I always accepted that larger wheels would go faster, and believed that 451s would offer a (very slightly) higher top speed than 406s

For the really fast guys that's probably true. If you are spending much time riding in a roadie peloton at 35+ km/h then top end gearing becomes important and that is one of the drawbacks of small wheels: It's more difficult to get high gearing using standard components, to be able to keep a sensible cadence at very high speeds. But for most people that should be the least of their worries.

As I mentioned, my Bike Friday tops out at 95 gear inches with its 52/36 crank and the 11-34 cassette with 451 wheels with 20 x 1 3/8" tires. A regular 700C with 25-622 tires and a 50/34 crank with an 11T smallest cog gives you a 120" top gear. To me that top gear is useless because I could only use it for very short intervals on a downhill. But if you're racing, you do need tall top gears because you'll be drafting other people at high speed and you'll probably have the legs to go with that speed. That is why Shimano created the Capreo hubs with a 9T smallest cog on the cassette, for people who want very tall gears on small wheeled bikes. Going from 11T to 9T brings you back in line with 700C road gearing. But arguably cyclists on small wheels couldn't care less about what cadence they would have to pedal at 45 km/h to stay in the TdF peloton if small wheels were permitted by the UCI as they once were.

As the number indicates, 406 tires have a smaller bead seat diameter than 451 tires, but they are also wider. Because of this the widest 406 tires actually have a bigger circumference than the narrowest 451 tires, but most are indeed smaller, even if not by as much as the numeric designation would lead you to believe. Consequently they won't give you quite as a high a top gear, but they will roll more comfortably because of the bigger air volume and the wider footprint that allows them to deal better with ruts and cracks in the road. basically the same thing as I said before about 20 x 1 1/8 vs 20 x 1 3/8. Also, a wider lower pressure tire is less likely to puncture than a narrow high pressure tire.

In real world, non-racing conditions the top gear almost never matters. Rolling resistance, safety, comfort and puncture risks should be more important considerations.
 

Slowburner

Cruising
Sep 27, 2019
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Riders determined to throw money around will want ceramic bearings.
Dunno how they work for cyclists, but I have both ceramics and ABEC-9* bearings on my boards, and absolutely love the ceramics.

* or so they’re called. Close reading makes me think the nomenclature is effectively meaningless, but they are very nice bearings, and nearly as smooth and fast as the ceramics.
 

Slowburner

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Sep 27, 2019
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Before joining them, see this video of Hambini's: .
Great link, thank you. The whole ‘Engineering graduate cutting up stuff with an angle grinder in his Dad’s garage’ thing is terrific, and I’m still laughing at “take care with the sparks; my nuts got roasted”. If he’s not a lecturer, he should be.
 

Slowburner

Cruising
Sep 27, 2019
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Update: I went back to Hasirin in Kashiwa yesterday and tested several bikes back to back, including the Dahon Horize Disk and Dash P8, the Tern Verge D9 and Verge N8; your input was very useful indeed, thank you all.

The staff were incredibly helpful, letting me ride a decent ten minute+ test circuit on each, then lining the bikes up so I could do a quick spin around the block, and hop on to the next, all of which made it very easy to focus on their differences.

I realised that ‘smoothness’ (and someone said early [link to follow]) might cover a multitude of factors, some of which are actually undesirable. Bikes with a giant hinge in the middle can have a degree of ‘bendyness’ (as we structural engineers like to say) that might well be smooth in the sense of comfy, but which isn’t great if you’re trying to take off from the ‘lights to stay ahead of traffic.

So the most comfortable ride was from Tern bikes, and their more refined designs, but upon closer scrutiny, I began to feel this was a sophisticated management of the inherent limitations. They also had the best folds and (although it’s beyond my scope of own interest) anyone looking to Brompton’s for foldability should probably also check out Tern’s remarkable new BYB.

By contrast, the Dahon Horize has the clunkiest fold (another design engineering term ;-), and the Dash P8 has the least convenient fold, being two hinges in the top tube and down tubes of a conventional style frame, rather than a single main tube that requires a hex wrench. Once I actually rode the bikes however, I realised the P8’s conventional frame provides a fundamentally different experience to the single-tube bikes in terms of how it responds to rider effort.

Small folding bikes are about the urban environment which for my riding style in particular seems to be about stopping and starting efficiently (and sometimes in a hurry to avoid careless drivers or unwary pedestrians). Riding these bikes back to back left no doubt that the P8 is the better design for the actual cycling experience (and damn the annoying folding experience!)

It occurs to me that a better investigation would be to compare these bikes with a road bike and full suspension mountain bike at the same price point. I just fear the experience would drive a man to full sized bikes, quick release levers, and rinko bags ... ;)

Finally, I could use some more input on another difference with the P8. It has a conventional stem with the bars forward of the stem, whereas all the others have beanstalks with the bars on top (or only slightly forward). Would the bikes with long stems feel better if the handlebars were more farther forward, or is it just the flexibility that’s making them feel less secure?
 
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