Ah! In use I've had no problem - much more stable & confidence inspiring than the typical car 2Tonne ones. It might be a bit of a visual thing, because these ramps are quite a bit bigger - rather longer than typical (& wider).the flat top before you hit the rear of the ramp its a little short dosnt give the wheel enough flat edge to run on before its stops
My sloping driveway is those large very smooth concrete slabs - so even more "skaty" than tarmac- esp with dust/grit/small stones that inevitably accumulate.I used to use a length of old seatbelt tied around the lower rung, but for the last 20 odd years on a sloping tarmac drive with lots of little loose stones (act as ball bearings) I just put the end of the ramp on an old rubber car mat. As soon as the wheel rolls against the lower rung it pushes it down, grips the drive and the ramp and up it goes.