Geometry and Handling

How a bike handles comes down to a handful of headline figures, with wheelbase and trail at the top. Understanding them makes it much easier to compare two geometries. But none of them acts alone: bike and rider form a dynamic system, and each figure changes how the others behave. These explanations are simplified on purpose, enough to compare bikes sensibly without getting lost in the detail. Go much deeper and it becomes very hard to pin any one feel on any one number. There's no single best geometry. This is how Tom thinks about it, so you can see the reasoning behind every Sturdy frame.

Wheelbase

Wheelbase is the distance between the two axles. It sets how sensitive the bike is to anything that changes its course: a movement of the bars, a lean, or a knock from the ground.

A longer wheelbase needs a bigger input to change direction, so the bike feels calmer and steadier. A shorter one responds sooner, which feels quick and lively, and it responds to bumps and small mistakes just as readily. Neither is better. It depends on the riding, and on the rest of the geometry.

Trail

Trail is the distance along the ground between where the steering axis meets the ground and where the tyre touches it. Because the tyre touches down behind the steering axis, the front wheel is drawn back into line whenever it's knocked off course.

More trail holds the wheel in line more firmly, and gives more feedback through the bars. The flip side is steering that's potentially heavier. Less trail is lighter to steer, but potentially vaguer. Trail is set by the head angle, the fork offset and the wheel and tyre size. The tyre adds a little of its own as well, because its contact patch flexes as it rolls.

Sturdy quotes trail measured along the ground, the way geometry charts do.

BB height: the next layer down

Practically, bottom bracket height is about pedal and ground clearance. For handling, it's a useful stand-in for the height of the combined centre of mass of bike and rider.

When a bike leans, a higher centre of mass sits further outside the tyres' footprint, so the bike needs a bigger movement underneath to get back under it. A shorter wheelbase moves the footprint further for a given input. As a rule of thumb, a higher BB pairs with a shorter wheelbase and a lower BB with a longer one. It's never decided in isolation, though: clearance, standover and tyre size all come into it.

Every Fosse and Drove frame has the same 78mm BB drop, so the tyre sets the BB height: roughly 263mm on 700×30mm tyres and 278mm on 700×45mm.

This is the layer below wheelbase and trail. Past here the system gets complex quickly, so treat it as a guide to comparing bikes, not a single right answer.

Using this to compare bikes

For fit, start with stack and reach. Then look at wheelbase and trail to see how two bikes are likely to differ in feel, and BB height after that.

The geometry comparison draws any two frames over each other, or a Fosse or Drove over the bike you ride now, with the differences side by side. If you'd rather work back from your current riding position, the size selector does that instead.