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Systematic method for choosing single speed gearing

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ilanpsi

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Discussion starter · #1 ·
Here is a systematic method I have come up with to find the appropriate gearing, assuming you have climbs that you need to do, you have a power meter and a minimum cadence requirement. I have to deal with short climbs as well as long climbs and I want to stay at least in the 40 rpm range. From my power meter, I know my power profile and what I can maintain for different times. I then look at the average grade of a climb, my weight + bike weight, which gives the corresponding speed, which gives the cadence given knowledge of the gear ratio and the tire size. The computations can be done using online power calculators and speed/cadence calculators. For example, I can maintain 250W for 5 minutes, at a body weight + bike weight of 82kg. So on an 8% grade, that's about 11.2kph at 250W, and 45 rpm in a 32x18 for a 2.2in 29" tire. So that gearing is appropriate for that terrain. However, my FTP is about 200W, and on a 10% grade, that gives 7.5kph at 200W, and only 40 rpm even on a 32x22. I would not want to do 40 rpm's hard for an hour, and a lower gear than 32x22 doesn't work elsewhere.

I live in Switzerland, and such long steep climbs are everywhere, which is why single speed mountain bikes don't exist here, as far as I can tell. Local bike shops have confirmed that they don't know of any, due to long steep climbs.

To get to trails, I need to do about 200m of climbing, consisting of repeated short steep grades, which in single speed, I have to do above threshold. So single speed rides for me are VO2 Max workouts. Since it has been shown that those should be limited to at most twice a week, I can't do these rides all the time.
 
#2 ·
It sounds like you are a good candidate for a dinglespeed setup. Have two front chainrings, and two rear sprockets that are two/three/four teeth apart (ex: gear one 32/18, gear two 30/20). This will allow you to drop the wheel, and manually derail the chain onto the other chainring/sprocket, affording you a climbing gear to get where you're going, but still have a decent gear to ride in.

You can tailor the gearing however you want, as long as the difference between the front/back sprockets are the same, so 33/17 and 30/24 would be the same chain length. I generally roll 4 teeth apart, and that's suitable for my area in both the flatter places, as well as the more hilly areas (~375m of elevation per kilometer, if I did my calculations correctly). I don't have any real sustained grades, though, as the longest uphill is roughly .5k long.

Just try both "gears" in the stand before you head out, since minor variations in machining can mean that one will be tighter than the other.
 
#3 · (Edited)
ilanpsi said:
To get to trails, I need to do about 200m of climbing, consisting of repeated short steep grades, which in single speed, I have to do above threshold. So single speed rides for me are VO2 Max workouts. Since it has been shown that those should be limited to at most twice a week, I can't do these rides all the time.
Click to expand...
It's normal here, the United States, for bike shops not to have single speeds as well. It's a niche here too. I live where it's similar terrain and you just have to be able to pick a gear you can live with. No gear is perfect unless you're just flying that day or have insane fitness. I recommend riding 32x22, spinning out on the flats at 13 mph, build fitness, and change your gearing.
 
#5 ·
Great post.

I’m on a 32x23 and get my breath by slow pedal where I can. For steeps during some big climbs (about 1k meters) my single pedal cadence drops to 2/3 of my breath, 3 breaths for every crank revolution so probably in the mid 30s. My continuous limit is somewhere between 7.5% and 9%, I know a long 9.5% is a hard no go, ruins me for rest of ride.

I’ve always imagined that there is a collection of ss nuts in the alp steeps, was going to visit and give it a try. I brought my ss to the Basque Country and it was super fun to explore but also a bunch of pushing the bike. Those sheep trails are no joke.

In pnw there’s ss mtb riders but you only find them out alone in the high places. No shops support them it’s an online thing.
 
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#6 ·
32:22 sounds reasonable. Your body will adapt. I started on 32:20 but dropped down for longer rides and to allow less effort in 'training'. 100km and 3000m climbing in an endurance event is very doable now, having been a very average rider a couple of years ago.

I pick ratio based upon spending about the same amount of time thinking I could do with a smaller ratio as I could a harder one, nothing more complex than that!
 
#7 ·
I just ride a geared bike and find the gear that works best on it by not shifting for a few rides. Once I figure what I can live with I get the same size chainring and cog for single speeding plus one cog with one less tooth for when I get in condition. Not sure how well that works with lots of climbing and then sustained downhills but works well here in Texas. Austin area is 34/20 and Houston is 34/15. With more climbing/grade I would have to drop the front chainring size a 20 is my max cog with my ss bikes.
 
#17 · (Edited)
baker said:
Explain, please...

Longer wearing due to more teeth sharing the load?

I don't miss my big ring at all in techy low clearance riding.
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Correct, there is less wear on the drivetrain. I run a magic gear, so that helps with the narrow window of chain wear.

There is less chordal action, i.e. the chain articulates less, so a fraction more efficient (says the obsessive racer).

I will admit that clearance can be an issue, but I started with eastern woods riding so I am biased.

Edit: Reference
 
#18 ·
I started off with easier gearing for the duration and elevation of rides in my area and kept changing cogs and rings. The "magic gear" combination did nothing for me.

Eventually, I reached a point where I can lean into pedal strokes on substantial climbs and not spin out elsewhere. That is about as systematic as it gets in my opinion.

For the trails I ride, my cog is smaller and chain ring larger than other SS riders. No one size fits all...

Current setups: 32x17 on 27.5" and 36x18 on 29er rigid SS's.
 
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#19 ·
letusride said:
Correct, there is less wear on the drivetrain. I run a magic gear, so that helps with the narrow window of chain wear.

There is less chordal action, i.e. the chain articulates less, so a fraction more efficient (says the obsessive racer).

I will admit that clearance can be an issue, but I started with eastern woods riding so I am biased.

Edit: Reference
Click to expand...
Meh, biggest contributor to drivetrain wear that I've experienced is still the chainline hands down. Still have not noticed any sign of faster wear (sharkfinning of teeth etc) from smaller ring/cog combos and I'm a clyde. I could believe that using even tooth ring/cog combo wears before ring/cog size combo.
 
#20 ·
Still enjoying 30:14. 27.5 x 3.0 plusser annnnnnd, lovin' it!
Wear annd tear has been minimal, thus far. The one speed automatic is the bike I reach for more often than not.

SS problem? No problem, I SS, I get trialsy, I grin, no problem...
 
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