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What is a Gravel Bike Part 1.


What is a Gravel Bike?

Welcome to the third topic of the VeloRoo / Pedal Brisbane / BOWY Boundless Gravel series where we aim to help you navigate the exciting new cycling category – “Gravel”.

At the same time via our socials, we’re peeling back Brisbane’s well ridden road loops to reveal where Brisbane’s best gravel can be unearthed.

So far we have explained What is Gravel Riding and Ranking Gravel Rides.

So, What IS a Gravel Bike? There are 3 main points which we will dive into a bit more in this blog.

Wondercross Wanderer with 650b wheels 1.75 inch mid block tyres

Summary Points

  • Gravel bikes DO look like road bikes. Here we’ll highlight the key physical differences.
  • Gravel bikes allow you to expand the scope of where you can ride. With a gravel bike’s bigger tyres, you can discover all the fun of multi surface riding that is hiding right beside your road loops!
  • Multi Surface riding requires easier gearing. Who knows what you’ll discover, so ideally your lowest gear ratio should be at least 1:1.

Do I need to buy a new Gravel Bike to ride Gravel?


Starting out on your Gravel Riding adventures you do not need to buy a new gravel bike. Gravel riding at it’s essence is a very welcoming and enjoyable way to enjoy bike riding. The journey is more important than the speed or destination, so, when you start out, just put on the skinniest tyres that will fit your mountain bike, or the biggest knobbliest tyres that will fit your old road bike, or make an old hybrid bike ride worthy – 1 Dusty Roo grade ride would be their recommended limits though – and head off and you WILL BE Gravel riding!

After a few rides you will begin to understand what sort of Gravel Riding gives you the most enjoyment, then you can decide which new Gravel Bike category will give you the best SPH – Smiles Per Hour – experience on your gravel adventures.

With your right Gravel Bike, gravel riding will be more fun, efficient, and will encourage you to continue expanding your horizons of where you can go gravel riding and the events you can do.

Why shouldn’t I just keep my Mountain Bike?

You can ride a mountain bike anywhere you’d ride a gravel bike, and indeed you’ll see many lightweight hardtails MTB’s (no rear suspension) with skinnier tires out on the trails and that’s great.

But flat MTB and Hybrid handlebars limit your hand positions, so can induce more fatigue on longer rides.

Less aero… while we’re not setting speed records, the more upright ride position means maintaining a pace on the road or faster sections is more demanding due to the less aerodynamic position.

The suspension, while it can add comfort, will also be heavier.

Finally, MTB geometry is aimed for going down hill, so any climbing is made more demanding on your fitness and again increases fatigue.

Isn’t a gravel bike just a Cyclo Cross Bike?

No. We’ve been asked this before.

A Cyclo Cross bike has gravel riding limitations. Tyre width, comfort, stability and versatility.

Cross bikes are pure bred race bikes designed for short, hard sandy, gravelly, grassy races where you’re only carrying your gnarlyest race face. The UCI (Union Cycliste Internationale, the world cycling governing body) limits tyre width to 33-35mm max in championship races.

They’re not designed for holding a straight line when you’re speeding down a gravel country road at 30plus kph, not does their geometry allow for comfort of longer hard pack (tarmac / cement / base layer gravel) sections.

Tell me, what makes a Gravel Bike an er Gravel Bike?

The beauty of modern gravel bikes is that they take the best elements of Road and Mountain Bikes and roll them into one.

However, like most things in life, there are choices which can make it overwhelming. We aim to simplify that for you in our gravel bile blog series. Choosing the right gravel bike may well be the only bike you need for everywhere you want to ride.

Gravel Bike DNA;

Think of Gravel Bikes evolving from each discipline of Road and MTB. It comes down to their fundamental geometries and intended uses and rider profiles. But we’ll delve further into that next time.

Meanwhile, here are the core fundamentals as we see it. If you have any questions, please feel free to hit us up!

Wheel & Tyre Sizes:

Intermediate tread on the left and knobbly on the right. Both 650b

Gravel bikes come in two tyre sizes. 700c and 650b.

If you are a roadie coming over, you’ll be familiar with 700c. A Mountain-biker though will be familiar with 3 sizes. 26 inch (Old school) 27.5 inch (latest generation) and 29 inch.

The 650b is the metric version of the 27.5 inch.

Tyre sizes can go from 32mm right the way through to 2.5 inches. Then the tread patterns are slick (not quite as slick as a road tyre) small block and large chunky knobbly blocks.

Have a close look at the Wondercross Wanderer below that has been fitted with the two wheel sizes and three tyre options. Same bike, 3 different gravel ride options = nirvana!

700c wheels 34mm slick tyres















650b wheels 1.75 inch small tread block















650b wheels 2.25 inch mid block tyres

It can be daunting about what to choose, but if you think of it as 700c gravel slick will be great on the road and solid surface bike paths and hard packed base gravel and dry clay. 1 Dusty Roo.

A 650b with 2.5 inch big knobbly tyre, terrible to ride on the road, but perfect for steep, loose rocky fire trail rides, where the tyre balloon offers some pneumatic suspension and tremendous grip and the lugs bite into the loose surface. 3 and 4 Dusty Roo’s.

Finally with tyres. You have two options. Tube or tubeless. With either options as the tyre size offers differing levels of pneumatic suspension, the tyre pressures are a LOT lower, especially with Tubeless, even down to as low as around 30psi. Squishy on the road, but great grip off it.

The last big difference between a gravel tyre and a road tyre is the durability of the tread and sidewall sections. Sharp, chunky gravel would chew a road tires to pieces, but the clever tyre manufacturers have developed rubber compounds that roll on hard surfaces, so they’re not as resistant to rolling as they used to be.

Gravel Bike Tyre clearance:

This is the guts of it!

Should your gravel adventure be greeted with Mother Nature showering you in tears of joy because your out enjoying nature, you need adequate tyre clearance to avoid sticky mud packing up between tyres and frame and grinding you to a halt. Finding and working the tool of trade… a stick to unclog said mud may produce tears of un-joy!

Alternatively as your whizzzz-ing along a gravelly country road, you don’t want rocks to get jammed up between tyre and frame/fork.

For me this is where I can rule out a lot of gravel bikes. I want the option to run both 650b and 700c wheels depending on if I’m gravelling or going for a road ride – as per the Wondercross photo examples above. On some bikes they are not interchangeable, meaning they become less versatile. And this is where understanding what sort of gravel riding appeals to you. You may be happy with one or the other. And that is cool!

Drive train set up:

You will have to choose whether you want a familiar 2x drivetrain – two chainrings on the front – or a 1x drivetrain – no front derailleur and a single ring in the front and a super-wide-range cassette in the back.

It comes down to preferences here.

The 2x obviously has a more gears and smaller ratio jumps between them. Road bikes have a 2x set up because the higher speeds on tarmac means you’ll be able to fine-tune your cadence and perfect gear. However, two rings and derailleur are obviously heavier, but the big disadvantage is complexity and front derailleurs can get clogged up on sloppy courses.

The biggest gear on this cassette is 42 tooth, however 52 teeth are common for exceptional climbing gearing for all conditions.



The 1x is lighter in weight but more easily serviced with the simplified drivetrain.

For me outright speed is not a major SPH factor on gravel and so I gladly swap that for better climbing options from the bigger gears available on the 1x set up.

Another bonus is if you wished to run a dropper seat post, you can use the left-hand shifter to activate the post.

The main downside is the big jumps between gears, meaning you can find yourself searching for an in-between gear you don’t have for your preferred cadence.


While gravel bikes have drop bars, a popular option is the dropped section is flared out to deliver more stability and control on technical descents. They also offer alternate hand positions so you have options to manage the natural hand and wrist fatigue which comes from riding the variety of surfaces gravel riding will offer. Brake set up can be tricky so that is a consideration you need to make of you replace the standard bars.


It goes without saying that really the only brakes to have a disc. Most are 160mm in diameter now. Like most things though, it comes to price points and cable operated are less costly.

The biggest differences are how they are operated.

Hydraulic is the most powerful and offers fantastic control.

But there are two types of cable operated brake calipers. Both are good and have pros and cons over full hydraulic brakes. They generally aren’t as powerful as hydraulic, however you are more likely to be able to do a road side repair with cable operated brakes than hydraulic. One system is a cable from the lever to the caliper. The other system runs a cable to the caliper, however the caliper itself is a hydraulic unit.


So that is what makes a gravel bike! A neat blend of road and mountain bike technologies.

In the next chapter, we will break down the various types of Gravel Bike, which help you identify the sort of Gravel Rider you might be. And we are also going to look at the various frame materials.

Thank you for joining us so far, and please feel free to share, comment or ask questions!

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