Many people would like to fit larger tires on their Harbor Freight frames. Below is information and dimensions based on the 4’x8’ Super Duty frame kit which comes with 12” wheels that have a 5 on 4.5 bolt pattern.
The Harbor Freight frames have 4.80 x 12” tires that are 20.5″ tall with 3” of back spacing. With the stock 48” width of the frame, there is 7/8” clearance between the tire side walls and frame rails.
When using taller tires, factor in the spring bolts because they cut sidewall clearance by ~3/8”. There are two primary approaches for putting taller tires on; adding hub spacers and narrowing the width of the frame rails. I like to have at least 1” of clearance between the tire side walls and frame rails. Another option is installing a wider replacement axle.
Two commonly available trailer tire sizes are; 175/13” which are 24” tall with 3.5” back spacing and 205/15” which are 27.3” tall with 4” back spacing. Note: These backspacing dimensions are based on standard zero off trailer wheels.
For putting 175/13” tires on, 1” of more clearance is necessary. The extra 1/2” of backspacing reduces clearance to 3/8”. The protruding spring bolt reduces clearance to 0.
For putting 205/15” tires on, 1.5” of more clearance is necessary. The extra 1” of backspacing causes 1/8” of interference. The protruding spring bolt adds an extra 3/8” of interference.