Gravel on a road bike: how to decide before the route decides for you

The classic version: brilliant road, beautiful morning, crest a rise, and there is 8 kilometres of loose gravel where the tarmac just ended. Nobody planned that. Something in the routing thought it was a road, and technically it was right.

Surface deserves to be a decision you make, not a discovery you have.

How routing engines see surface

The map records road surface — sealed, concrete, compacted, gravel, dirt, sand — along with the road classification. A router can use that in three broadly different ways:

Exclude. Unsealed roads are removed from consideration. Routes may get longer, but nothing dirty appears.

Tolerate. Unsealed roads are heavily penalised but usable, so a short connector or an unavoidable stretch is allowed rather than causing a 60-kilometre detour.

Welcome. Unsealed roads are treated as normal or preferred, which is what an adventure bike rider actually wants.

That is why setting a vehicle profile matters more than it looks. A sports tourer on road tyres and a big adventure bike on knobblies should not get the same route between the same two points, and a good app derives surface tolerance from what you told it you are riding.

The other half is disclosure: before you commit to a route, you should be able to see what percentage of it is unsealed and where those sections are. A number before you leave beats a surprise at 90 km/h.

Where the data is weaker

Be realistic about limits, because riders get caught by exactly this:

• Unrecorded roads. Plenty of minor roads have no surface listed at all. A router has to guess from road class, and guesses are wrong sometimes.
• Stale records. A road recorded as sealed in 2016 that has since broken up is still listed as sealed.
• Seasonal reality. A hard-packed gravel road in February and the same road after a week of rain are different propositions entirely, and no map captures that.
• Roadworks. Sealed road, currently loose gravel for 3 kilometres, for the next month.

Treat the unsealed percentage as a strong hint. Then read the road when you get there — if the surface looks worse than the plan said, the plan is wrong, not the road.

The gravel that actually hurts people

It is not the 12-kilometre section you can see coming and slow down for. It is:

• Gravel washed across the exit of a blind corner after rain.
• Loose stone at the crest where the grader pushed it.
• Spill from a driveway or a logging track on an otherwise clean road.
• Fine dust and marbles on the racing line of a good corner in summer.

Every one of those is invisible in map data. It is transient, local and current, which is why rider-reported hazards matter. Another rider hitting that corner twenty minutes ago and flagging it is the only system that can tell you — and hearing “gravel reported ahead” in your helmet before the corner is worth more than any amount of surface data.

If you are the rider who finds it, report it. It costs a tap at the next stop and it is the reason the report exists for you next time.

If you end up on it anyway

Assume you will, eventually, on road tyres. The technique is mostly about doing less, not more:

Before it: slow down while you are still on tarmac. Braking hard on the gravel itself is what puts people down. Get to a speed you are happy with before the surface changes.

On it:

• Off the front brake. If you must slow further, use the rear gently and engine braking.
• Steady, light throttle. Neutral or very slightly positive. Chopping the throttle mid-gravel unsettles the bike.
• Relax. Loose grip, loose elbows, let the bars move. A death grip transmits every wobble into a steering input.
• Weight back slightly. Take pressure off the front, which is the wheel that will wash out.
• Look where you want to go. Far ahead, not at the stones a metre in front of the wheel. Target fixation on gravel is real.
• Stay upright. Minimise lean. If you must change direction, do it with gentle steering rather than by leaning.
• Do not fight the wriggle. The bike moving underneath you on gravel is normal and it is usually self-correcting. Reacting hard to it is not.

Leaving it: watch for the lip where gravel meets tarmac, especially if it is a step. Cross it as square as you reasonably can.

Setting your app once, correctly

Do this before your next planned ride:

1. Set your vehicle. Whatever you actually ride, with the tyres it actually has.
2. Set surface tolerance to match. Road bike on sports tyres — sealed only. Sports tourer with a bit of appetite — tolerate short sections. Adventure bike — let it in.
3. Check the unsealed figure before saving any route. If it says 14%, look at where those sections are and decide deliberately.
4. Turn hazard alerts on so rider reports reach you before the corner rather than after it.

Gravel is a legitimate and fun part of riding for the right bike, the right tyres and the right rider. It is only a problem when nobody asked you first.