What Gear Ratio Should I Pick for Tracklocross?
Picking a gearing for setting up your first tracklocross build can be daunting. The first two recommendations I ever heard were to go with a 63″ gear inch or to go with a 2:1 ratio. These were both recommended to me in the dim and distant past and were for riding single speed offroad. It was so long ago we used 26″ wheels, remember them?
I honestly can’t wait for the bike trade to rediscover 26″ wheels. I wonder what it will do for the Boost and Super Boost standards. You know, the standards are designed to make 29er and 650b wheels as stiff as 26″ wheels with a quick-release axle. I’m so glad that mountain biking moved forward enough to admit that they should just have stuck with the old standard.
Now that I have people overheating as they bought into marketing bullshit, I’ll carry on.
The 2:1 ratio
As I said, the 2:1 ratio came to me through a grizzled single speeder. This means that your chainring should have double the number of teeth your rear cog has. For example, 32/16, 40/20, or even 44/22. It is pretty simple maths.
Now, I don’t know how the grizzled single speeder got the ratio, but I’m hoping Sheldon Brown appeared to him and passed on the knowledge. The idea that they might have gained this insight by riding bikes seems a little too atheist for me.
I do, though, find this ratio a pretty good place to start. Mainly because it isn’t as terrifying as recommending 1.78154343465767:1; even just looking at this ratio gives me flashbacks to high school, and I can feel a sweat mustering up on my forehead.
This is handy, as this is the ratio that Surly Bikes recommend for 700 c wheel bikes. Okay, they don’t, really. They recommend 1.78:1. Still, it is a little more terrifying than 2:1. Some of us might even want to break out the calculator for this one.
How did Surly get to 1.78:1? The 2:1 ratio works well for 26″ wheels, but for tracklocross purposes, we tend to ride 700 c wheels. 700 c wheels are bigger than 26″ wheels. To prove that, we can look at the diameter of our wheels. A 26″ wheel is 559 mm in diameter, and a 700 c wheel is 622 mm in diameter. You’ll see those numbers on tube boxes or the side of your tyres.
Want to know something cool? 559 mm is 22″, and 622 mm is 24.5″. Wheel and tyre sizes are fun.
Bigger wheels, bigger ratios
Let us jump back a second. A 2:1 ratio means that for each rotation of your cranks, then your rear wheel will have gone round two times. A 1.78:1 ratio will mean that your rear wheel will have gone around 1.78 times instead of two times. You’ll have gone less far, but you’ll find it easier if you keep your wheel sizes the same.
You might find yourself wanting extra speed on the flats or downhills with a 1.78:1 ratio, but it will be easier on hills. That is why the grizzled single speeder recommended a 2:1 ratio. It is a good midway point for most people. If you find hills easy, then increase your ratio. If you find hills hard, decrease your ratio.
So, we’ve now all agreed that 2:1 is an excellent ratio for single speeding on a 26″ wheeled bike offroad. Why, then, am I and Surly suggesting a 1.78:1 gear ratio for 700c wheels?
So, to make the maths more straightforward, I will use a 1.8 ratio. I’m lazy like that. I’m also going to use a 40 tooth front ring and a 20 tooth rear cog.
Using a 40/20 ratio and pedalling at 90 rpm on a 700 c wheel with a 2″ tyre, I will be rolling at 15.3 miles per hour.
Using a 40/20 ratio and pedalling at 90 rpm on a 26″ wheel with a 2″ tyre, I will be rolling at 13.9 miles per hour.
As you can see, the 26″ wheel bike is going slower. We can then look at the gear inches. On the 700 c wheel, we are riding a 56.98 gear inch, and on the 26″ wheel, we are riding a 52.02 gear inch. A lower gear inch means we’re not going to find pedalling as hard. Our 26″ 2:1 ratio is then harder to ride on a 700 c wheel.
When riding on the road with 700 c wheels, this ratio might not be an issue, but when you’re riding offroad, it is easier to be riding a bit slower and with a bit less effort (the mud will make the effort seem the same), and it will make your knees a bit happier. We then change the rear cog on our 700 c wheel to a 22 tooth cog. We’ll find we have a gear inch of 51.85 and a speed of 13.9 miles per hour. 40/22 gives us 1.8:1, which is, for me, close enough to 1.78.
So there you go, don’t fear a ratio of 1.8:1. Start from there and work your way out.
If you have 700 c wheels, you’ll want to start riding tracklocross with a 30/17, 32/18, 34/19, 36/20, 37/21, 39/22, 41/23 or 43/24. These are an excellent place to start, and then once you know where you are primarily riding and how you feel, you can begin to dial in your perfect gear combo from there.
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