You could fit a 9.5" wide slick on a 7" rim quite safely... Probably a 10.5" but it might be a little bulgy. Hoosier makes a 26x9.5" QTP, you could go with a 235 drag radial, whatever floats your boat.
I have completely stock suspension and can effortlessly cut 1.70 60 fts on 27x10.5" Hoosier QTP's with a very light burnout (it'll go 1.60's next time out...)
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