I haven't been cycling that long. 2-3 years on a mountain bike before adding a road bike this last year and a half. While MTBing I was more into 20-30 mile rides with 2-4k of climbing and singletrack. On the road I have done one organized century, a few solo centuries and most recently the Markleeville Death Ride. The Death Ride is a 130 mile ride with 15,000' of climbing in the eastern California Sierras. I came through it well. I was tired but not overly so. I had a moving time of 9:30 with a total time of 10:30.

I was thinking about trying the Mt. Tam double century in a few weeks which is 200 miles and 15,000'. Instead of being at an average elevation of 7,000', it's near sea level. Since additional training is out of the question, does anyone think I should give it a shot or will I just get a smack down? What are the things I should be worried about making the jump from 130 to 200 miles? For those who have made the transition to being an endurance rider, what sage advice can you share?

TIA