I have had a 12 and currently have a 13. I broke the sub-frame on my 12 and had few other problems. The 13 was a huge improvement over the 12. I did break my sub-frame on the 13 but it was my fault, I was running on a flat tire that split and was on held on at the rim lock. I rode several miles like this and the sub-frame cracked from the tire hitting the sub-frame. It broke in a completely different spot than the 12. I would say they fixed the sub-frame in 13.