SportsCrafters Progressive Mag Trainer Works great for single rear wheel trikes (or bikes with the use of our Fork Stand) and requires no clamping on the rear skewer Accommodates 20" and larger wheels Two 3.25 heavy-duty, lathe-turned aluminum drums allow you to use your stock tires to train. Mag resistance is invisible, ultimately reliable and nearly noiseless (yes, you will hear the drive train of your bike or trike) High-tech design using eddy currents (so you can baffle your friends when you place a paper clip on an aluminum drum and it sticks!)