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20 inch wheels?

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20 inch wheels?

05-22-18, 06:17 PM
#1
Dake2
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20 inch wheels?

I am thinking about buying a folding bike with 20 inch wheels. But I am having trouble getting my head around the physics of riding a bike with 20 inch wheels. Using the same gear ratio as I would use riding my bike with 700c wheels, and turning the same number of revolutions per minute, how much slower will I be going on the 20 inch wheels if I am riding at 15 miles per hour on the 700c wheels. Thanks

Last edited by Dake2; 05-22-18 at 08:36 PM.
05-22-18, 06:25 PM
#2
Abu Mahendra
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Originally Posted by Dake2
I am thinking about buying a folding bike with 20 inch wheels. But I am having trouble getting my head around the physics of riding a bike with 20 inch wheels. Using the same gear ratio as I would use riding my bike with 700cm wheels, and turning the same number of revolutions per minute, how much slower will I be going on the 20 inch wheels if I am riding at 15 miles per hour on the 700 cm wheels. Thanks
The math is roughly 406/622 or 0.65. One turn of a ISO406 wheel covers the same distance as 0.65 of a turn of a 700c wheel. Inversely one turn of a 700c wheel covers the same distance as 1.53 turns of a 406 wheel. So, same gear, same cadence, 15 miles per hour on a 700c bike is about 10miles per hour on a 406 wheel.

btw, the most common 20" wheel is ISO406, but there's also ISO451. I own both types. There's a lot of ignorance and prejudice of small wheel bikes (i.e. 451 or smaller). Head over to the Folding Bicycles channel for solid info.

Last edited by Abu Mahendra; 05-22-18 at 11:47 PM.
05-22-18, 07:14 PM
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Dake2
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Really? Modern bikes have something called gearing? So it sounds like you are saying I would need to turn a bigger gear to keep up with someone riding a bike with larger wheels.
05-22-18, 07:18 PM
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Kapusta
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Originally Posted by Dake2
Really? Modern bikes have something called gearing? So it sounds like you are saying I would need to turn a bigger gear to keep up with someone riding a bike with larger wheels.
Yes, and thus small wheeled bikes often geared higher.
05-22-18, 07:26 PM
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Abu Mahendra
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Originally Posted by Dake2
Really? Modern bikes have something called gearing? So it sounds like you are saying I would need to turn a bigger gear to keep up with someone riding a bike with larger wheels.
You have the following options to raise gearing, on any bike, big or small wheel:
1. bigger chainring
2. internal gear crankset ala Patterson Drive
3. 9T rear sproket cogset ala Shimano Capreo
4. IGH ala SRAM DualDrive

This rig of mine had 125 gear-inches at the top at one time...
05-22-18, 07:42 PM
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Dake2
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Best looking folding bike I have seen! What brand is your bike? Thanks for the info.
05-22-18, 07:56 PM
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prathmann
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As one example, my Bike Friday with nominal 20" wheels (451mm rims) has a large chain ring with 60 teeth and the smallest cog with 11 teeth. That gives it about the same high gear as my 700c (622mm rim) Cannondale with a 53 tooth chain ring and a 13 tooth rear cog. The force with which I need to push the pedals and the cadence on both bikes will be the same if I'm riding both at the same speed.

There are a variety of ways to give small-wheeled bikes reasonably high gears. On mine it's using a larger than usual chain ring, others use an internal rear hub gear (usually 3-speed) in addition to the cassette gears. Another way is to use Shimano's Capreo cassette which has cogs going down to 9 teeth instead of the usual 11. Then there's the option of using a step-up gear built into the bottom bracket (see Schlumpf Speed Drive).

So there's no reason to think that you'd be using the same gear ratios when riding a bike with smaller wheels than the 700c wheels you're used to. And, BTW, you certainly don't have "700 cm" wheels - those would be 23 feet in diameter.

Last edited by prathmann; 05-22-18 at 08:01 PM.
05-22-18, 07:57 PM
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BlazingPedals
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If you want the equivalent of a 52T chainring on a 700c wheel, but on a 406 wheel (assuming the same cassette,) than you'll need something like a 62T big ring. The problem with bigger rings is, derailleurs can only handle so many teeth of difference between rings, and as the rings get bigger, you max out the derailleurs and have to accept smaller % steps between the rings. Which is to say, if you want full-range gearing on a small wheel, you have to resort to more drastic measures.

I think that most folders and citi-bikes use lower gearing, because they're just not as fast and so don't need the big gears.
05-22-18, 07:58 PM
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Abu Mahendra
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This dog?

It is a Dahon Dash, the little brother to my Dahon Dash Altena...

25-99GI on tap

Originally Posted by Dake2
Best looking folding bike I have seen! What brand is your bike? Thanks for the info.

Last edited by Abu Mahendra; 05-22-18 at 08:07 PM.
05-22-18, 08:38 PM
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Dake2
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I stand corrected 700c not 700 cm.
05-22-18, 08:59 PM
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1nterceptor
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Instead of relying on people's opinion on the internet; I suggest to try some folding bikes for yourself
and get first hand experience/knowledge.

My folding bike with 16 in tires(349 ETRTO); keeping and passing other bikes w/ 20 inch, 26 inch, 700c,
29 inch, etc. wheels:
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05-23-18, 08:07 AM
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Kapusta
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Originally Posted by 1nterceptor
Instead of relying on people's opinion on the internet; I suggest to try some folding bikes for yourself
and get first hand experience/knowledge.

My folding bike with 16 in tires(349 ETRTO); keeping and passing other bikes w/ 20 inch, 26 inch, 700c,
29 inch, etc. wheels:
To be fair, you can pass 90% of the people on the 5 Boro ride with square wheels and no chain.
05-23-18, 10:42 AM
#13
fietsbob
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Imo

20" especially in 406, is likely about the most abundant rire size on the globe ...

451 is a thin go fast rim - tire, 406 is a more rugged rim - tire combo..
both are nominally 20"

...

Last edited by fietsbob; 07-16-18 at 11:10 PM.
05-23-18, 11:04 AM
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CliffordK
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Originally Posted by BlazingPedals
If you want the equivalent of a 52T chainring on a 700c wheel, but on a 406 wheel (assuming the same cassette,) than you'll need something like a 62T big ring. The problem with bigger rings is, derailleurs can only handle so many teeth of difference between rings, and as the rings get bigger, you max out the derailleurs and have to accept smaller % steps between the rings. Which is to say, if you want full-range gearing on a small wheel, you have to resort to more drastic measures.

I think that most folders and citi-bikes use lower gearing, because they're just not as fast and so don't need the big gears.
I'll admit that I've had issues with front derailleurs and big rings in general, for a couple of reasons, some with intended range, some with frame design.

However, Say you use a 60 or 70T outer ring, then the logical choice is to use say a 50T inner ring. And you should be able to shift it with most front derailleurs.
05-23-18, 11:33 AM
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Leisesturm
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Originally Posted by Dake2
Best looking folding bike I have seen! What brand is your bike? Thanks for the info.
I don't think that bike folds. It has 20" wheels, yes, but I'm not seeing a folding mechanism anywhere.
05-23-18, 11:40 AM
#16
JA TREK
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I'm thinking of selling my 20" folder with brand new tires (only rode on once for 1 mile) and a tune-up if you're interested! It has 3 gears and shifter works. It's in NY. I love the bike, just don't use it enough.
05-23-18, 11:51 AM
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fietsbob
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Mini Velos are a non folding 20" wheel road bike , often discussed here ..

no hinges means it can be lighter, too.
05-23-18, 07:29 PM
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20 inch wheels would look so cool
05-23-18, 10:28 PM
#19
atwl77
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Originally Posted by Leisesturm
I don't think that bike folds. It has 20" wheels, yes, but I'm not seeing a folding mechanism anywhere.
That Dahon Dash, as well as the Altena, are both folding mini-velos.
05-24-18, 12:27 AM
#20
Abu Mahendra
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Originally Posted by Leisesturm
I don't think that bike folds. It has 20" wheels, yes, but I'm not seeing a folding mechanism anywhere.
Come again?

it folds via a LockJaw hinge on the top-tube and on the down-tube which clamp down with an Allen key on a set of inter-locking teeth. Zero flex. Six years on--it is a 2012 model--the hinge Mechanism is still tight, free of play or give. Frame, fork, dereilleur hanger and headset weigh 3.1kg. Not über-light, but not a porker either. And best of all, the bike is affordably priced, and requires no proprietary parts save for the hinges. The downsides? It is far from the smallest fold, one size only so tall folks are out of luck, and Dahon stopped making them in 2016 so they are tough to find on the sale block.

Last edited by Abu Mahendra; 05-24-18 at 11:55 PM.
05-24-18, 01:34 AM
#21
atwl77
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Originally Posted by Abu Mahendra
What bag are you using for your Dash? Most 20" bags that I have found do not fit.
05-24-18, 02:58 AM
#22
50PlusCycling
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I ride a Birdy folder with 20" wheels. I run Panaracer Minits at 115 psi, the suspension on the bike keeps the ride smooth even at high tire pressures. A Dura Ace/XTR 11 speed drive line gives me enough gearing, a 56t front chain ring gives me more top end. It's light, fast, folds up small, and fits my body the same as my full size road bikes.
05-24-18, 05:01 AM
#23
Abu Mahendra
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Originally Posted by atwl77
What bag are you using for your Dash? Most 20" bags that I have found do not fit.
A 'Giant'-branded bag purchased at the Giant store across the street from the Taitung train station in Taiwan.
05-24-18, 09:32 AM
#24
Retro Grouch
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[QUOTE=1nterceptor;20355088]Instead of relying on people's opinion on the internet; I suggest to try some folding bikes for yourself
and get first hand experience/knowledge.

How fast will it go? How hard will I have to work? How well will it shift? How do the small wheels handle? Wouldn't take much of a test ride to determine those things. That way you'll know for sure.
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Last edited by Retro Grouch; 05-24-18 at 09:52 AM.
05-28-18, 10:12 AM
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Jax Rhapsody
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