Before you tweak your diet I would check out Phil Maffetone and his training methods. I am an avid mtn biker and would blow up and get my arse kicked by the sugar burners on regular basis until I tried his training. You need to train under your specific heart rate to avoid the bonk and slowly build it over time. When properly conditioned you should be able to keep up and ultimately prevail at the end as the sugar burners tend to burn out easily. Word of caution though, if they step it up during the ride at anytime and you try to keep up and get out of your heart rate zone you will blow up. It takes some commitment and trust but once you buy into it you will be rewarded. Here's a link to get started, he also has a book out (long read but worth it even though there are a few nutritional recommendations I don't agree with but overall ok) Phil Maffetone, www.philmaffetone.com - 180-Formula
You'll never see the light if you're in someone else's shadow, or said another way, life is like a dog sled team, if you're not the lead dog, the scenery never changes