If they're super dirty, you may want to hose them down with a sharp stream of water and then toss 'em in the washing machine on a somewhat gentle cycle - I've washed mine that way about 6 or 8 times now and they still look like new. In fact, I did it again today after some stinky mud got on them from our NCCX outing yesterday.

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Cheers!, -John
NCCX http://www.geocities.com/norcal_clubx