If you have repeated problems with tires aging and cracking, both on your bike and car, check to see if you're parking them near something in your garage that has an electric motor. Supposedly, ozone given off by an electric motor can cause such aging in the rubber. (I hope I'm remembering that right. If not, more knowledgeable types with actual chemistry training and such can feel free to flame away.)
New tires often cure lots of ills. I know money's tight, but that's the last place to scrimp.