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I want to buy a entry-level folding bike for slow-speed commuting, involving 20 minutes ride going over a steep hill of 1500 foot (500 meters). It is concrete 'normal car road', not off-road.

What gear-inch value should I look for in choosing a simple beginner bike suitable for the given task.

Would a 6-speed folding bike with 20 inches wheel and xxx gear-inch value be adequate? That is, have enough 'low gear' to comfortably-and-slowly going over the hill and no need for more expensive 21-speeder?

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    It would be rare for a 6-speed bike to have the same range as a 21-speed bike. It could be done, but the single derailer & associated cogset would be non-standard and hard to shift smoothly, due to the wide range of sizes. – Daniel R Hicks Mar 1 '16 at 13:33
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    @Daniel. Let me re-phrase and forget the 'maximum', as I am not looking for a racing road bike. Would a 6 speed folding bike have similar minimum gear inches as more expensive 21 speeder? That is, a 6-speeder can do the above described task as a 'slow hill climbing' commuter and I do NOT need to buy a 21-speeder. – EEd Mar 1 '16 at 14:25
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    If you've got standard components on there (and on folders it's a big if) you could reduce the size of the chainring to get lower gearing. – Chris H Mar 1 '16 at 14:55
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    You can use Sheldon's gear calculator. Enter the specifics from each bike, and compare the gear inches that it gives you. – Kibbee Mar 1 '16 at 14:55
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    SE cannot judge what gearing you need for for this steep hill. You could borrow a mtn bike and see what gear you actually need. – paparazzo Mar 1 '16 at 16:25
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The simple answer is no (to the 21 speed vs. 7 speed question having similar minimum range). The better answer is yes if the single front chainring matches the # of teeth of the smallest chainring on the 21 speed.

Remember that with a 20" diameter tire, even a 1:1 ratio (20 gear inches) is a decent hill climbing gear. For example, on my 21 speed bike, I have 26" diameter tires and a 24/28 lowest gear so that is about 22.3 gear inches so if you had say a 34/34 setup (with 20" tires), your gear would be even lower than mine. To beat 1:1 on a 20" tire I would need 24/32 gearing on my bike which is possible but would cost me some money to get. I would say shoot for 20 gear inches and go from there.

Whoever recommended borrowing someone else's bike and testing that first seems like good advice. That will give you a baseline to tweak your gearing from.

What you may want to try is gear the bike so you can normally make the hill in the 2nd to lowest gear, thus giving you 1 more bailout gear for when you are extra tired. Condition yourself to be able to make it up in 2nd gear but you will have the assurance of having 1 lower gear. For example, instead of a 34/34 setup being your lowest gear, you can make it so you have 28/28 as your next to lowest gear, then you will have 28/34 as your bailout gear, which with 20" tires, would give you about 16.5 gear inches.

Finally, yes I think if you don't go ultra low on the lowest gear, then a wide range 6 speed should also suffice for normal "flat" riding and coasting downhills. For example, 28 teeth in the front and 11,14,18,23,28,34 in the rear would give you a gear inch range of 16.5 low to about 51 high. Just F.Y.I. (and for reference), my favorite and most used gear on my 21 speed is 34/20 which with my 26" tires gives me 44 gear inches so even if your smallest cog is 13 (not 11), you will be at 43 gear inches in top gear, good for a leisurely 9 to 10 MPH (14.5 to 16 kph) pace comfortably.

Good luck!

  • Excellent answer - I've added paragraphs to ease reading. – Criggie Mar 2 '16 at 0:05
  • @David, from web info, as-shipped front chain ring is likely around 40 teeth. If I were to get 1:1 gear ratio, around 20 gear-inches and 5 kmh 'walking' (steep up 550 meters hill) speed at 60 RPM pedal, I need to convert to a dual chain rings system, with 2x and 4x teeth. Am I thinking along the right path? Appreciate pointers on getting such a conversion kit (does the kit has a proper name) and modifications instructions (web sites, instructables). – EEd Mar 2 '16 at 9:13
  • But I thought one of your requirements was low cost as you eluded to by asking "no need for more expensive 21 speeder?" Since you stated low speed riding, why not just change the front chainring from 40 something to 20 something, shorten the chain accordingly, and be done with the gears? Also, some people are concerned about an exact 1:1 gear ratio so you may want to make the front chainring at least 1 tooth away from any cog size such as 29/28 instead of 28/28. I also see folding bikes with 16" tires so there you would not even need an underdrive gear for that for hills. – David Mar 2 '16 at 12:01
  • @David. Agreed. Also, what is the concern for 1 tooth away? I wonder to what extend 16 inches is (said by a local Olympic cyclist on TV interview) less stable than 20 inches. It was bad news memory. A retired Policeman loss control when going downhill and lost his life. TV news showed his 16 incher was un-damaged. Witness said he was throw off and hit his head. – EEd Mar 2 '16 at 13:54
  • Concern for not having an exact 1:1 gear ratio is less stress on components or so some people claim. A 29/28 gear or a 27/28 gear is supposedly better than a 28/28 gear. Not sure about the 16" incident. If they are very unsafe then I would assume they could not be sold. Also what about skateboarders that also go fast but have MUCH smaller wheels? They also have folding bikes with 14" tires so 16" tires is not the lower practical limit. Many kids bikes have tires smaller than 16" diameter so if safety was an issue, ask yourself how can they sell those. – David Mar 2 '16 at 14:16
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The folding bikes come in 2 sizes: 16" and 20". 20" is mainly used, and the only reason to go 16" is to save space while folded.

For the gears. Your front chainring will be about 48-52 teeth. Rear cogs if you going for 6 speed will have about the 13-26 teeth range. That brings you to 1:2 ratio. Not to hard, but not the easiest one.
As folded bikes lack front gears, maybe you will be better with 7 speed MegaRange cogs, that will give you 14-34 teeth range, that will be good for the hardest parts of hills, and when you will be tired.
You can also change the front chainring to a compact one (42 teeth) that will make your easiest gear even easier, but will also affect the hardest gear to be easier and slower.

Yet, 20" is pretty uncomfortable to ride when compared to 26" wheels, and the only reason to go for a folding bike is when one have a problem to transport the bike.

  • That is not the only reason people choose 16". The smaller tire also affects gearing. They also come in 14" tire size. Here is a link: alibaba.com/product-detail/… – David Mar 2 '16 at 12:18

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