Understeer is when the front tires reach the limit of their grip before the rears, so the kart turns less than the steering input asks for and runs wide of the intended apex. Drivers often call it "push," because the kart pushes on toward the outside of the corner even though the wheel is turned.
What it feels like: you add steering and the nose keeps washing wide instead of tightening the line. Adding more lock usually makes it worse, because the front tires are already sliding.
The useful thing for a developing driver is that understeer has two very different kinds of cause, and it's worth ruling out the free one first:
- Driver-induced. Carrying too much entry speed, turning in too early, a sudden steering input, or gripping the wheel so hard you can't feel the front all produce understeer that no setup change will fix.
- Setup- or kart-induced. Front geometry, tire pressures, weight distribution, and — on a solid-axle kart — how well the inside rear unloads all affect mid-corner grip. Those belong to the setup side.
Because a kart has no differential, a mid-corner push is often really the inside rear staying loaded and dragging, which is a chassis question rather than a front-grip one. That distinction is exactly what is it the kart or is it you? is for, and the chassis mechanism sits in diagnosing hopping and binding.
See also: Oversteer, Racing line fundamentals. Related terms: apex, turn-in.