Tire and rim size absolutley can limit payload. In some cases you give up strength for the "bling" effect of 20 inch rims and low sidewalls.

 

I believe it's less due to the stock 20" pirelli's being a P (passenger) rated tire not a LT or higher load tire

 

The Sticker on the Driver's door (Tread Act Sticker) is the payload rating of YOUR Truck based on the Options. The Rating 1500+ lbs listed in the sales Literature is the MAX POSSIBLE Payload for that Body style (a Base version of the truck - no options)

I have a 2009 F150 Platinum SCREW 4x4 - the Tread Act Sticker indicates 1096 LBS. The Trucks GVWR is 7200 lbs (On the Vin Sticker on the door) Well here's the reality - My Truck weighs with ONLY me in it (190) and a full Tank of fuel 6320 LBS . So that leaves me with 880 lbs of Payload (aditional Passengers, cargo and yes tongue weight) in the Truck.

In defense fo Ford, this Advertised Payload is done the Same for all Manfactures (GM, Dodge, Toyota). So if you want to compare Payloads, look at the Tread Act sticker on each vehicle . I would guess that your Tacuma had a much lower rating than the Advertised Rating.

So while i believe MY Truck can handle more that me and 880 lbs of Payload/Cargo, IF I WANT TO BE LEGAL, my limit is 880 lbs. with me in the Truck.

 

I thought that to with my Truck, but the Pirelli's have a Rating of over 2400# per tire. While the yellow stick is the Tread Act Sticker and seems to be connected to the Tires, due the math on my Truck and you see that Tread Act Number is based on the Truck's GVWR (7200) minus the actual Trucks weight

Truck weight minus Me (190) (6320-190=6130)

7200 - 6130 (Truck w/o me in it ) = 1070 for payload

and the sticker says 1096 (Okay 26 lbs different - well that would account for the SOFT Tonneau I have on the 5.5 box.

So the Pirelli's aren't the determining factor - it is just simple math the Trucks GVWR (7200 for My F150) minus the ACTUAL Weight of my Truck (with all it's Options) - what is left is your 'legal' payload and posted on the sticker on the D Door.

The 275/55R20's Have a 111T Rating that's a 2403 lb weight rating and 118 mph speed rating.

So with 4 Pirelli's the Truck should handle a load of 9612 lbs - way more than the Trucks 7200# GVWR -