Gearing experiment…but what’s the answer?! Ratios & confusion

Just to add, this won’t be a commute only bike

I plan to use this on days when I fancy a bit of a challenge and don’t want to take the geared mtb so light XC type riding with less technical sections

You'll have a massive compromise between road and off-road ratios.

My SS MTB is a 29er, running 32:19 in the Lake District. I had a Langster which was 42:16 iirc, on a not flat commute.

Good news is rear sprockets can be had cheaply so it's just a case of seeing what works.

@breadcrumb thankyou for that

Really I’d be looking at off more than on road

I guess, through all the babbling of my original post, what I REALLY mean is

On 700c wheels I found a sweet spot (for me) with a 32 & 13 but I’m struggling to work out how that would translate/transfer to the slightly smaller(?!) 27.5 wheels

Have a look for a gear inches calculator 👍

https://sheldonbrown.com/gear-calc.html

According to maths, and for these purposes let's assume you stick with a 32T up front - as sprocket size goes up it gets easier. If wheel size is fixed, how much easier is just the ratio of sprocket sizes - double the sprocket size, it gets twice as easy / half as hard.

Same with wheels except other way bigger wheel = harder (ignoring arguments about rolling resistance and angle of attack on bumps, etc.)

If you start changing both - then as above you need a gear inch calculator or maths to see how they interact or cancel each other out.

So to actually answer your question - if 32:13 and 700c is right, then 32:13 on 27.5 will be NOMINALLY 1.8% easier.

Real world - even on flattish off road / light XC what you can comfortably ride on roads and cycle paths and what you can actually climb hills on will be quite different. Even bigger / draggier tyres will 'cost' you a couple of sprockets larger in probability. And when the compromise is being a bit too spinny for the commute but rideable on XC, vs perfect for the commute and off and pushing on XC - the former wins every time.

Why not repeat your experiment on the terrain it'll mainly be used on and see what the hardest gear you can manage your bigger climbs on is. Then either fit that as a gear, or if it seems way too spinny on the flat fit a harder gear and either accept some climbs are meant to be walked (or toughen up a bit). But I suspect it'll be around 32:18 in reality.

And remember, in singlespeed you are using schroedingers gears - it'll be the wrong gear pretty much all the time but at the same time it's also the right one, because it's the one you have.

32x17 sounds like a good starting point for MTB unless you ride somewhere very flat.

I run 32/19 on a 29er for local stuff, mostly off road trails in and around Leeds. Quite up and down here, but nothing too steep or sustained. If I commute on the SS MTB, (still trails, but more flat tarmac) its a bit more spinny, but OK.

Mate has just gone SS on his 27.5+ HT, running 30/17 on 2.6 tyres (mine are 2.3), he's slightly lower geared than I am, and is considering 30/18.

So, depends how flat (or not) your riding is.

You also need to take into account tyre size, both in terms of overall diameter, and the fact that a chunkier more treaded MTB tyre will be draggier and not roll as well.

A 27.5 wheel will be lower geared than a 29er wheel, all other things being equal, as the wheel travels less distance per rotation.

It sounds like 32/17 might be a bit spinny for your commute, but is probably quite a good gear if most of your riding will be offroad.

I might have a few sprockets you could try out, will check, but probably have 14, 16, 17. Happy to let you borrow them, so just cost of postage, then you can either keep whichever suits and return the rest, or return them all when you've decided which is the right ratio and are ready to buy a new one.

Sounds like a good opportunity for a dinglespeed?

I used to run 42 x 17 (700c) 67 inch gear on my commuter and 32 x 16 (26 inch) 52inch gear on my mountain bike. If I was cycling in the Dark Peak I would sometimes swap to 32 x 18, 46 inch gear.
My commute was flat.

Just a thought: are ovals any good for single speeding? Other than the chain wrap giving a slightly inconsistent chain tension through a rotation I can imagine it's the ideal use for one.

I'd recommend using Sheldon Browns gear calculator gain ratio method, as it takes into account crank, wheel and tyre size. You can pick a cassette from the list if you want all ratios but I just tend to pop in the easiest and hardest gears or the individual ratio I'm interested in.

Take each of your bikes and note down the ratios you think might work for singlespeed. Punch these into the gear calculator so you get a feel of what the numbers mean and the different between 2.9 and 3.1. Stick them in a spreadsheet and then see what other cog sizes offer that ratio i.e 30*18 and 32*20 are about the same gear.

This are the numbers when I jumped from 26" to 29", and also helped when I switched to belt drive as changing ratio would be much more expensive.

[img] [/img]

Just a thought: are ovals any good for single speeding? Other than the chain wrap giving a slightly inconsistent chain tension through a rotation I can imagine it’s the ideal use for one.

Yes, I used to have one when I had a singlespeed and it worked well.

There is some variable tension, but in reality the eccentricity of the oval ring is not that much, and it barely matters compared to the chainstay length. Mine was on sliding dropouts, never had an issue.

Thankyou, all, for the replies and helpful advice so far, a fair bit to chew on and more of it making a bit more sense

I’ve been putting numbers into gear calculator and I THINK my initial idea of 32x17 would have been WAY off of where I’d like it to be

According to gearcalc…
Current 700c wheels on 32x13 = 66.88gear inches

The closest I can get (for purposes of comparison) to that with 27.5 wheels is 66.89 gear inches via 32x13, I’m thinking I’d like it just a tad less spinny on the flats without making climbs unbearable, so have started thinking that 32x12, which brings me up (or is it down?!) to 72.60 gear inches might be a good starting point, in hindsight, 32x17 would have been too low (or is it high?!) for my liking

As luck would have it also, the conversion kit I’m buying comes with a 12t sprocket, winner!

@hardtailonly thankyou, sir, for the very kind offer, I’m going to get this thing built up and try it with the 12t for now and see how it feels so I may still come a knocking yet

Many thanks again for the info / advice and knowledge, do keep it coming…

As you get used to SS you’ll get used to spinning faster.

I use 39:18 for (hilly) 700x35 commuter work and 33:19 or 18 on the 29er. 32:18 is good too.

Point is, gear down and spin more. If you choose a comfy gear on road it’ll be annoying tall off road for obstacles and corners/mud etc.

If you’re experimenting, try 32:16 on 27.5 equivalent and see how that is, assuming you’ll spin your max cadence for a decent flat road pace.

I've got to be honest. If you can genuinely ride 32:13 or 32:12 on "light XC type riding with less technical sections" then you'll be cleaning up in races because even the best XC SSer's are on 32:16 to 32:18 typically.

Alternatively - I ran 32:18 on a 29er SS 10 years ago when I was (comparatively) fit

Spinning that at a sustainable but not ridiculously fast 100rpm meant I could do 15mph; 80 rpm as a normalish offroad cadence is 12mph, 'monkey with tinsel being pulled out of its arse' 120rpm = 18mph

Your 32:12 would have you doing  21.5mph at 100 rpm, 17mph at 80rpm. That's an average sort of cadence, if you can do 17mph on light XC type riding I'd be amazed.

@IA @theotherjonv excellent points and well made, think I might have started overthinking without the knowledge / experience that SHOULD come with it,

Following your points, I’m Thinking it might be wise(r) to start with a lower gear and work up until I find a sweet spot so am edging back to the idea of 32x17 as my starting point

32*13 to 32*17 is a huge jump.

I'm not sure you are going to find a gear that works for you for both commuting and off-road.

My bike is geared for off-road and is really not that much fun on roads or bike paths unless you are not in a rush. High cadence light load is the only scenario that tends to cause me knee pain. I avoid it as much as possible. Similarly, 32*13 off-road is going to be miserable on any sort of bad surface or decent hill unless you are extremely strong!

IN these discussion it is always best to talk gear inches rather than nn x nn.

67 GI off road is VERY high and higher than I used on my road fixed gear bike (I can spin though)

55 GI was good for off road where I live but an absolute chore to ride on road sections. Such is single speed...

As per earlier post, if still not sure stick your geared bike in 32:12 or 32:13 and try and ride that up your light XC hills and I think you'll realise. Then try again to see what gear you can 'just about' manage on those hills and add a couple of teeth for fatigue, etc., or a couple less if it's daft low and accept you'll have to walk some - such is the way of the SS. It'll always be a compromise. Just remember - one gear but three speeds, sit down, stand up, get off and push.

Once settled on the ratio, then of course consider finally the actual ratio. If 32:16 is right then of course use it, but be aware that 32:17 is much better - particularly as 17 is a prime number then the chain will land on different teeth each rotation of the chain, and thus even out the wear as the same front to rear match will only occur (if my maths is right) every 544 rotations of the chain.

32:16 is particularly bad because it's an exact multiple, 32:18 slightly better although not great as both are even, 32:19 good again (but you might then also consider 34:19 - but not 34:17 of course!)

Just something else to make you think as you select your ratio.

“light XC type riding with less technical sections” then you’ll be cleaning up in races because even the best XC SSer’s are on 32:16 to 32:18 typically.

To add to this, I won Bristol bikefest pairs on SS one year, that’s pretty much the definition of light XC, most of it is on a blue man made trail, and that was on 32:18 29er, my teammate on 32:16 26er.

It’s also 7km for me across town to/from the trails and whilst the mtb is slower than my commuter it’s not disastrous, and less than you’d think given traffic etc.

The gear ratio only really matters on the flat. Uphill it’s your legs and lungs providing the limit, downhill regardless of ratio at any decent speed you’re not pedalling much.

SS doesn’t hurt on the hills, that’s naive. SS hurts when you’re on a road linking section with your geared mates and they’re going juuust too fast so you’re having to hold max rpm for minutes at a time. Proper fire in the legs then.

I agree - I was certainly fitter but by no means superathlete, but when i started riding SS I thought I'd only be fit enough to use it for 90 minute blasts in the woods at night for minimal maintenance type rides, and indeed it was great for that. I thought it WOULDN'T be for longer multi-hour / half day rides all around the area (typical SE army land, linking fireroads and then singletrack blasts)

To my surprise, actually that was also fine - simply because on the flat unless you are trying to keep up with faster geared friends, you are limited and once you realise and accept it then they become recovery. Just spin along at 90, doing whatever speed that gives you and accept you'll get to the next bit when you do. Wheareas on a geared bike you almost feel compelled to keep clicking into higher gears just because they're there.

I’m running 30:18 with 165mm cranks and 29x2.4 tyres. Works great for MTBing around the South Downs (which are quite hilly) but it’s incredibly annoying on the occasional route commute, spins out far too early.

On a related note, once you have settled on a ratio I thoroughly recommend an eccentric bb adapter thingy if you don't have sliding dropouts.

My SS has a threaded BB and 24mm Hollowtech cranks, so I used a trickstuff-excentriker. If you have a larger BB shell there are many cheaper options.

Runs much quieter than with a tensioner, although my homebrew BB mounted one was much quieter than the usual hanger mounted one.

I gained a lot from centering the chainring, surprising how off centre they can be.

Re the gearing you will learn to spin! SS cured me of pushing big gears on the road bike, I'm a right twiddler now.

SS bikes seem more efficient (less weight?) so a gear you struggle to turn uphill on gears will come within reach and you will get stronger.

Embrace the constantly wrong gear!

Folks, thankyou all again for the comments and advice, still loads to digest

I think I might have to get out on the mtb and ride a handful of my regular loops sticking to one gear (there’s 12 to choose from) and seeing how it feels, I can be sure to get it spot on as it also has the same wheels and tyres as the ones I have for the single speed…just have to wait for the rain and generally pants weather to do one…

Thanks for the recommendation re: EBB, fortunately it’s a Surly 1x1 frame I’m building up so paired with a tuggnut, I’ve got sliding dropouts for days

Ideally you really want tugs either side if it's horizontal dropouts BTW. It's not just the pedalling force that make the wheel want to move, it's the brake. Especially if you're using a QR rather than a nutted axle you can properly crank down on.

And if you have the nutted axle, remember to carry a means to undo it for punctures.

Following your points, I’m Thinking it might be wise(r) to start with a lower gear and work up until I find a sweet spot so am edging back to the idea of 32×17 as my starting point

~52" is a sensible starting point (32x17 with a normal sized 27.5 MTB tyre).

Most people go lower! Because unless the route is really un-technical and flat you'll never find a gear low enough for the climbs, so the lower the gear (bigger sprocket) the faster you will be. And any gear will always spin out on the descents, and if it's spun out it doesn't matter if it's by a little or a lot. A big gear is only of any benefit on a flat road.

The only time I've really picked the wrong gear was SSUK in Comrie, riding the 250miles up there in 32-20 was soul destroying on the road sections! Still wasn't low enough on the race itself 😂. Isle of Wight the year before i was in 32-14 which was great on the road and the beach. Hard work off-road though.

In general it's better (and faster, and easier) to learn to pedal at 100+rpm, than to try and build the muscles needed to grind a big gear.

I’ve been riding mixed terrain and routes on my 29er ss for a few months now. I settled at near 61” gear and accepted that some of the uphill I’d be walking. It has worked out as a good compromise gear given that I use it for lanes and roads. I’d not go any larger. Live and ride in South Wales.
For ref it’s 36/17 with 2.1” tyres.
I do this once a month on the ss.
https://flic.kr/p/2ows5mt
There are 3 parts on the large climb where I have to walk 50/60 yards.

Thankyou once again for all the advice and tips, has been a great help and cleared a few things up

I have since taken the “big bike” (Identiti AKA 12 speed, 27.5x2.35, 32t up front) on some of my regular, quick (10 miles or so) local loops of mixed terrain which includes gravel paths, rooty woods, bridleways, muddy/grassy fields, some steep climbs and roads that connect different sections, sticking to one gear on each pass

For me, of the gears I tried and thought worth a mention…
16x32 - quite an easy (nice) pedal, not too hard going, not spinning out TOO easily on the flat bits even when trying to see how quickly it would take, a bit of a grind up some of the climbs but managed it, albeit slowly, without really feeling the need to get off and push

18x32 - again, quite an easy pedal, the off-road bits and climbs were much quicker / more comfortable, without spinning out although felt like I was getting close at times, the flat bits, I found, again quite nice and easy with little effort but did spin out quicker than I would have liked when trying to really gun it

I think, following my initial thoughts, and advice on here, 32x17 may actually be the one, riding the 16 and 18 (which both made for a nice enough pedal in different ways) I THINK I can feel where the 17t sprocket would sit in regards to feel being in between the two, I suspect it would cover a lot of my riding quite nicely and as has been mentioned, could well suit some of my longer days too (which was always part of the plan)

I think I’m going to order a 17t sprocket along with the conversion kit (that comes with a 12t in the box) and see how it feels, the sprockets aren’t too much of a layout each so it might even be handy to have some different sized spares if it goes that far

Meanwhile…I’ve got everything I need to build this bike up now with exception of SS conversion kit, some headset spacers and a seatpost, has only taken 6 months to amass parts…I’m so excited I could s*** ha ha

another thing, maybe for later, is to consider a flat bar and bar end set up (you can do risers and bar ends too, but..... you know....)

It might be a small thing but having something really to pull against when thrutching up a proper hard climb just adds that extra 5% that can make a difference.

Cane Creek Ergos were my choice

https://canecreek.com/product/ergo-control-bar-ends/

I found, again quite nice and easy with little effort but did spin out quicker than I would have liked when trying to really gun it

You'll find this at some point whatever gear you pick. Part of the fun of SS is then trying to maintain that speed through pumping and just plain braking less. There's also an inbuilt advantage that you quickly learn what speed you can pedal, so you instinctively know whether to pedal out of a corner or pump/coast. And without gears to think about it's surprising how much more time you have to pump a dip/berm because you're not having to put in a light crank or two to shift gear.

@theotherjonv great suggestion that but I do have them on my flat bar commuter / gravel bike and have found I don’t use them at all, really, the only reason I haven’t taken them off yet is because I’m too lazy to replace the grips too ha ha

@thisnotaspoon some hardy advice there, sir, will definitely be trying to push the boundaries either way of what I can / can’t do with no extra levers to worry about