Steve - How tight is this course, can you do it on a bigger bike?
I did it about 3 years back on my XChallenge.
The heavens opened about 15 minutes before the start, and it made the event a total nightmare. i still got round a got a finish with about 6 laps.
I found it hard. Bloody hard. My wrist was strapped up for a month after, due to a inflammed tendon sheath- probably from trying to hang onto the bars and fight with the bike.
There are photo's and a brief report on this thread:
http://www.ukgser.com/forums/showthread.php?t=206406&highlight=Tidworth
If it's dry you should be ok on something like a 690 or sorted XChallenge, but anything bigger and i think it would be a DNF for most of use mere mortals.
I think the problem is the ground gets so slippery and greasy, you will struggle to hoist the front end, which is regularly needed for crossing the many ruts and ditches that litter the off road training area. The mud is like grease, and once over the bike it is very difficult to hang on.
If your not sure go, along as a traveling marshal and see how your bike fares

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Good luck
