Question W vs Z

My dad is looking into some Pilots for his Tiger. There is a set of Z rated (149mph) and W (168) (i believe). This mph is calculated by running it that fast for ten min or something but anyway.

My questions: What is the mileage difference? will the Z wear out faster? The tire must give up something to only get a Z rating right?

Thanks for all helpful responses.

Dont matter. One is ok to handle the heat of sustained operation at 149 the other at 168 or more. I just doesnt matter. Its not a measure of treadwear only the ability to disapate heat.

Are the compounds different?