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What is the lowest rideable gear ratio (chainring/cassette) possible without feeling like having to balance/trackstand? I'm doing some virtual simulations right now and I'm just setting up IRL limits. If it differs on road and mountain tires, I'd like ratios of both.

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    I've voted to close as this is entirely subjective based on the riders skill. A rider with good balance that is able to perform a trackstand would be able to ride an impossibly small gear. A 10t chainring paired to a 60t sprocket would give 1mph, which would be possible to ride, but not possible to buy
    – Andy P
    Jun 6, 2019 at 8:14
  • So many variables to consider, but logic says the wider the tire the easier it will be to balance at slower speeds
    – Dan K
    Jun 6, 2019 at 9:53
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    @AndyP: I kind of agree, but maybe OP is also interested in availability or technical feasibility? For example I have a feeling that the increased torque could be a problem for the rear wheel and with very small chainrings the chain could snap …
    – Michael
    Jun 6, 2019 at 12:27

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One issue is that it can be harder to balance a bike while spinning like crazy than while pedalling more sedately. Timing a gap in traffic, for example, I can get below 1km/h, but changing right down is a mistake because when I want to get going again I'm trying to push 100rpm after a couple of strokes. This is worse if I take the MTB on road, because of its smaller small chainring - it has very limited use.

Another is that gearing too low produces too much torque, which is worse on steel uphills. With your weight on the saddle or over the back wheel, the front wheel will lift, but with your weight forwards the back will slip. I've had this on trails (MTB) and wet roads (tourer). You have to push quite hard to get up enough speed to get through the weakest part of the stroke (when the pedals are vertical) so simply starting gently isn't an option either. Because of the grip, this heavily depends on the surface, so it's not just about the bike.

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One bike I ride has a lowest forward speed at which I can balance of around 4.3 km/h. Any less than that and it gets too tippy. These speeds are best attained going up a significantly steep grade of 10%+ and its a lot of concentration to react in time.

So to answer your question, what's the slowest speed you can ride at while maintaining your balance? Figure that out, perhaps on the flat and on an uphill, then work backward from there.

I feel this is one of those questions where the asker has an idea, and formulates a question. But the answerers can't see why the question helps the idea.

Instead, consider expanding your question to show your ideas and your end goal. More minds may help you get there better and faster.

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    Me and my colleagues are testing what chainring size paired with a 50T cassette cog would be sufficient as a granny/bail-out gear for our trails here (which consist of steep rural footpaths) but we don't know if something as low as a 20-22T would be practically 'unrideable' or not and we wanted to lessen our sample sizes (we'll be buying chainrings of every tooth count), so I'm asking for advice here on which smallest chainring should we start with. (based on your experiences of course)
    – Gregory Leo
    Jun 6, 2019 at 9:34
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    A 30T chainring with the 50T cassette would be equivalent to the popular 22/36 ratio. I'd say a 26T ring might be about the lowest usable ratio. It's not so much balance that will be the problem, but when pedalling off road at very low speeds, you no longer have the momentum to roll over rocks/roots and the bike will 'stall' easily.
    – Andy P
    Jun 6, 2019 at 10:43
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    I can comfortably ride at 2km/h on the flat. But on steep inclines 4 km/h is the lower limit. When it gets even steeper shiftng my weight forward impedes my ability to balance even more. Lose ground and loss of traction too. What the OP might get at best are sets of curves of lowest speed over incline for different bike geometries and surfaces.
    – gschenk
    Jun 6, 2019 at 12:47
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    @GregoryLeo Instead of buying every size chainring, you should probably just do a binary search algorithm. Try a 30t and a 10t, 10 will probably be unrideable, then you buy a 20t, if 20t is rideable, you try a 15t, if not, try a 25t. Keep on going to the midpoint until you find something that works. No point in buying everything between 15 and 30 if you only need to buy 5-6 of them to figure out the answer. Also, you might want to check out if you have a local bike co-op that would let you try out various used parts for free (or really cheap) rather than buying everything new.
    – Kibbee
    Jun 6, 2019 at 12:53
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    @GregoryLeo Perhaps buying the single smallest chainring you can fit on your crank would be the best start.
    – Criggie ♦
    Jun 6, 2019 at 19:44

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