Recently I ran across these ramps as a new product in the "Griot's Garage" catalog. Griot's Garage is located in Tacoma, Washington (800) 345-5789 and carry many high quality items for the care and maintenance of your car. The ramps are a direct answer to the problem of either changing the oil, detailing the undercarriage or any other maintenance activity without raising the car with a floorjack and jack stands. The ramps are rated at 6500 lbs. gross vehicle weight with a 7 1/2"overall lift.
What makes these ramps so versatile is the 2 piece extension ramps made of ABS polymer that extend to a 15" transition from the ground level to the ramp. This allows a Miata to easily drive up the ramps for work. The ramps will not move or push when driving onto them. A pair of wheel chocks are available for $14.95 and are made of heavy gauge steel that fit nice and tight to the rear wheels. Works better and is much safer than a pair of sawed of 2x4's. Also the 4"x15" non-sink plastic polymer base can be easily attached to the front bottom of the ramp to prevent the ramps from mushing down in soft gravel, asphalt or dirt. As soon as I received the ramps and extensions, I tried them out. As with any ramp up situation it's a good idea to have a spotter while you drive the car up the ramp. The ramps and extension kit didn't slip at all and provided plenty of clearance for "Snubby" on the way up and down for his oil change and undercarriage detail.
The ramps and extension kit sell for $69.95 and the wheel chocks for $14.95. These are high quality products, as all are at Griot's, and come highly recommended, especially if you are having a hard time finding any similar ramp set for your Miata.