Do you find that your gearing is just too high for steep climbs or fully loaded bikepacking gear?
If you struggle to get up steep climbs or spend long days in the saddle on a bikepacking trip, you probably need a granny gear. Despite the name, a granny gear isn’t just for grandmothers.
But what is a granny gear? And how can you set one up on your bike?
While the exact definition varies from cyclist to cyclist, a “granny gear” most often refers to the smallest chainring of a triple chainset, which gives you access to very low gears.
To get you up to speed, we’ll be covering:
- Granny Gear Meaning
- Why Would You Want A Granny Gear?
- What Is A Good Granny Gear Setup?
Let’s dive into granny gear bikes!
Granny Gear Meaning
The definition of a “granny gear” for many isn’t completely clear.
You might hear many definitions thrown around: the smallest chainring on a triple? The smallest chainring on any old crankset? The lowest gear on your bike in general?
Well, there’s no one-size-fits-all answer, unfortunately.
The smallest chainring on a triple crankset is one of the most common answers. A triple is a crankset with three chainrings. Often, these are 53-tooth, 39-tooth, and 30-tooth, or a similar combination.
The rule for the crankset is simple: the smaller the chainring (fewer teeth), the easier the gear.
Triples have somewhat gone out of fashion in recent years and aren’t that common anymore, but they actually offer a huge amount of versatility. You essentially have the range of both a sub-compact and a standard double crankset.
However, the “smallest chainring on a triple” definition only tells half the story.
The difficulty of a gear combination is determined by two numbers: the size of the chainring at the front and the size of the sprocket in the cassette at the back.
The easier a gear is to push, the lower the gear ratio is. The gear ratio is the ratio between the number of teeth on the chainring and the number of teeth on the cassette sprocket. You can work this out by dividing the first (front) number by the second (back) number.
So, perhaps the last definition is the most accurate: the “granny gear” is just the lowest gear that you have on your bike.
This means that you can create a granny gear in a 1x system, too. You could have a 38-tooth chainring paired with a “dinner plate” 51-tooth sprocket at the back, giving a gear ratio of 0.745.
Notice that this is a lower gear than if you had a triple on a road bike with, for example, a 28-tooth sprocket at the back, giving a ratio of 1.07. This means that every revolution of the pedals will result in almost a third of a revolution more of the wheels.
- Check out our Ultimate Guide To Bike Gear Ratios (With Bike Gear Ratio Calculator) here!
Although the strict mechanical definition is a little hazy, the essence of a granny gear is clear.
It is an extremely low gear that allows you to turn the pedals in any situation.
You may be moving at walking pace, but that doesn’t matter. Getting up a brutally steep climb, fully loaded with all your gear, without dismounting, is an achievement no matter your speed.
Why Would You Want A Granny Gear?
Have you ever completely blown your doors whilst bikepacking or after a long day of relentless climbing?
Well, most people (including us) definitely have. You’re feeling faint, there’s a searing pain in your legs, neck, and back, and as much effort as you put in, even on your lowest gear, you just cannot turn the pedals even one more time.
But why?
Likely, you’ve simply gotten your gearing wrong. Don’t worry; it’s an easy mistake to make. We’ve all done it at some point. Your lowest gear just wasn’t low enough and has forced you to maintain an unsustainable speed.
You need a granny gear!
This is a very common problem, especially with new bikepackers. You’re used to a relatively high gearing on your road bike, and you don’t have any problems getting up hills or going on long rides. But when you add an extra 20 kg, this will no longer be the case.
When you’re bikepacking, you need to get going at a pace that feels much too slow. This is because you’re going to tire a lot more quickly with all that weight, especially if you’re going to be in the saddle for most of the day.
So, the solution to this problem is to widen your gear range.
With a very wide gear range, you will be the proud owner of a granny gear, the lowest gear of your wide range that you can use when you’re climbing or going over tough terrain, or god forbid when the worst has happened: you’ve bonked.
Even if you’re not going bikepacking, it’s never really a disadvantage to have a granny gear.
As long as you’ve got a wide range, so you can still hit the higher speeds when necessary, it’s just nice to know the granny gear is there if you need it. Perhaps you’ll be able to get up that 30% climb you’ve always pushed the bike for or be able to cycle further than before.
If you’re serious about training efficiently, then a granny gear can come in handy here too. Zone 2 training has recently been shown to have a huge impact on your fitness.
When you’re doing Zone 2 rides, it’s imperative that you stick within your Zone 2 bounds. Going up to Zone 3, even just for a short while, will compromise the effectiveness of your Zone 2 ride. It will take your body 20-30 minutes to return to Zone 2.
This can be especially difficult if you live somewhere super hilly. Sure, you can make it up the climb easily, but staying in Zone 2 is another story. It can be really difficult to remain in Zone 2 on steep climbs, especially if your gear range isn’t wide enough.
Perhaps a granny gear would help you out here, too. You’ll be able to stay in Zone 2 with ease, dawdling up the climb at walking speed, but at least you won’t compromise your training.
What Is A Good Granny Gear Setup?
So, you’ve established that a granny gear is a necessity for you. But what’s a good setup?
Well, it depends on what kind of bike you’ve got and what type of riding you’re doing. Regardless, a good, functional granny gear will usually have a gear ratio of below 1:1.
Quick disclaimer: check the compatibility of your derailleur before trying to extend your cassette’s range. Most road groupsets allow up to 34 as a maximum, gravel groupsets often allow up to 42, and mountain bike groups vary, but 51 is often a reasonable maximum.
Firstly, let’s talk about gravel bikes. On a gravel bike, you’re likely to have a 1x or 2x setup. If you’ve got a 2x, you’ll probably have a sub-compact (46/30) crankset.
Say you want to go bikepacking on your gravel bike. Then it could be sensible to extend your gear range at the back. If you’ve got a gravel-specific groupset such as GRX, it’s likely the max you’ll be able to have at the back is 42.
But, paired with a sub-compact chainset, you’ll have a minimum gear ratio of 0.71, which you should be able to use up essentially any climb on any terrain.
A road bike is a bit more difficult. Given the maximum sprocket at the back is likely to be 34, even with this, you’re likely to have to switch out your chainset too to get a true “granny ring”.
Luckily, you can usually fit a sub-compact chainset at the front, lowering your granny gear ratio to 0.88, which should be more than enough for bikepacking – especially when you consider the decreased rolling resistance and drag due to road tires and geometry.
If you’ve got a mountain bike, you’re probably already sorted. Most modern mountain bikes come equipped with some crazy-low gear ratios as stock so that you can get back up to the top of your downhill trail without having to dismount.
But, if for some reason you don’t, then get yourself a “dinner plate” sprocket for the back. Whatever number of teeth you have on the front, a 51-tooth at the back will give you a suitable granny gear for all your bikepacking needs!
Now You Know All About Granny Gears…
It’s time to decide whether to install one for yourself!
Granny gears – whether you take that to mean a triple-crankset setup or just a super-low gear option – are certainly not for everyone.
Racers are very unlikely to use them, and if you’re a serious cyclist with excellent fitness you’ll probably find a granny gear is unnecessary.
Triple cranksets went out of fashion for a reason, too: they increase the overlap between gear combinations, add weight, require triple-specific components, and result in more extreme cross-chaining angles.
However, for heavily-laden bikepackers or for casual cyclists who are just cycling for the fun of it rather than hunting hill-climb records, granny gear bikes can make perfect sense.
As with all things bike-related: if it increases your enjoyment and makes you more likely to jump on the bike, go for it!
