I originally posted this in the MTB section, but I think it's more appropriate here...

I'm coming off another great cyclocross season and am looking forward to next spring and getting back out on the mtn bike. I am considering trying my hand at at least one longer endurance type race for next summer. Up until now, I've never done much over a typical 25-35 mile xc race, though I have done some longer running events, and one xterra tri. I'm looking into several options - 6 hr solo, team 24 hr, and/or possibly a longer 60-100 mile race.

So, for those of you with experience transitioning from shorter faster races to longer endurance events...
Any suggestions as to a good, comprehensive preparation program out there?
Good training/nutrition websites?
Good core and cross training suggestions?
Any specific changes to my bike that I should consider - ergon grips, gearing suggestions, wheel preferences? (going to use my Felt Virtue, and not planning any major upgrades, and yes I realize there's a lot of personal preference here, and that the race course will matter a great deal)

Really, my biggest concern is properly preparing my body. How far in advance to start building a base... How many hours to put in per week, and how to spread them out, things to be cautious of... That sort of thing.

I know everyone's different, but any suggestions are appreciated. Thanks!

Whilst there can be a fair bit of very good advice given to you on this forum it would sound that you really need a coach, and they will be able to a) answer all of your questions and b) put it into a meaningful and structured plan for you. The amount of time for what you ask is perhaps a little disproportionate as to what can be put on a forum.

_________________
"Physiology is all just propaganda and lies... all waiting to be disproven by the next study."
"I'm not a real doctor; But I am a real worm; I am an actual worm." - TMBG

I have some experience in endurance events - have ridden a handful of 12 hour solo's and five 100 mile races, with progressively better results.

Recommendations:
Try to get in one long (~1/2 of estimated race length) per week leading up to the event. Use this ride to test race nutrition (a HUGE part of success in endurance racing), pacing, and make any tweaks needed to the bike. Ideally this ride would be on the mountain bike, on terrain similar to what you'll be racing on.

I'm not too concerned about core strength/cross training. IMO making the training as specific as possible (i.e. riding) will give the most improvement but some strength training throughout the year can be helpful for especially long or rough courses to limit arm/shoulder/back/neck fatigue.

I use and recommend ESI Chunky grips. I have used Ergon's in the past but find the ESI's equally comfortable, lighter (this is WW's!) and allow better control on technical trails.

For wheels/tires, think reliability over weight. Relatively sturdy tires on NoTubes (or similar rims) with sealant is a safe bet. I've had good luck converting 60tpi Maxxis tires (Crossmark, etc.) to tubeless - no cuts or flats in three years of riding/racing.