If I'm not mistaken, the R300 was the Cannondale 3.0 frame. That frame had spacing on the rear axle for 7-speed (126mm), not 8-speed and above (130 mm). You can put an 8-speed or larger cog wheel on it, but you have to stretch it to make it fit. This works better with steel bikes than it does with aluminum. I did it for a few years on a R400 and eventually, the frame broke at the drop outs. I was so glad to get rid of that bike -- it rode like being on a rail. You can probably still find 7-speed stuff if you want to put new components on it. Consult Agent 319 for ebay tips. If it were me, I'd toss it and buy a new bike.