No not a retail store, but I have all the sizing charts. I usually say go 1/8" larger then your measured size to leave room for headphones or a balaclava. usually it does not bump up a size. hat size is measured around the LARGEST part of your head. I am focusing on my Service and track side support, I can't run a retail store too. Although I wish I could.

With the new Snell regulations coming out in about 12 months, you may want to consider waiting if you use the helmet for motorcycle use too. the 2005 and 2010 Motorcycle Regulations are incompatible with each other, this does not matter for an autocross application since it's changes in the force/load, and Visor penetration requirements not exactly an issue when you have a windshield in front of you. Snell Memorial foundation regulations can be found at http://www.SMF.org

The SA 2010 regulations are still unpublished, but I assume some minor changes.