The Delta seatpost rack can handel 30+ lbs with ease. I have been using one for the past year with great success. The only issue it that if they are ounted to high, you will get a bit of sway in the rear of the bike. But if you can mount then lower like on a sloped frame or a MTB frame then the center of gravity is lower and then it is hardly noticable. I have tired it on a road bike and a sloped frame Hybrid like the Sirrus and they work alot better on the Hybid (and I do a 35 mile round trip commute over some cinderpack trails here in Philly that are often washed out when it rains).