All E-Series, cutaway and stripped chassis like used on Axis/Vegas, use 16-inch tires as far as I know. And these size tires typically have much higher speed rating than larger commercial truck tires. On E-Series RVs if speed is limited to 80 or less, I would not expect it to be due to tire speed rating.
I've driven a few E-Series vans and Class Cs and haven't noticed a speed limit, although none were newer models. I also usually keep speed lower than 75 MPH.
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