"I know I have to take 198 out of Visalia..."
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198 between the Foothills Visitors Center (up the road from the Ash Mountain entrance) and Potwisha is *not advised* for vehicles over 24'. Yes, it can be done in a large/long vehicle, but the road is narrow and curvy, and meeting another vehicle, coming from the other direction on a curve (where they often take part of your already very skimpy "lane"), particularly if your "mountain driving skills" are limited, can be an adventure. Since you seem determined to take 198, enjoy the trip. :R