Depends if you are talking the front end, or the rear end. I have stack of five 2X12s bolted together. Each board is slightly longer and the ends are cut as a diagonal, so it works like a ramp. This gets me about 8 inches. I have driven the front of my Dad's W22 onto these ramps and it works just fine. One could probably get away with maybe one board higher, but I don't think I would go higher than that without a wider more stable base. I think you could build ramps about 10 inches high, and then put blocks under the hydraulic jacks to lift it the rest of the way. Just make sure the jacks do not take too much weight off the front wheels, as it would be very unstable.