They will kill your rpm, you don't have enough gear or power to run those tires yet, the 26" x 10.5" would be best. The 28" tires will fit if you trim the wheel opening and bang the inner fender in, you may also need to trim the rear ground effect so that when the tires grow they do not rub.
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[b]12.16 @ 113.5, 1.78 60ft..no traction in the 90 degree