4G payload question

Newbie here, hoping someone can clarify...
On Toyota.com: comparing SR5 4WD double cab long bed with TRD sport 4WD double cab long bed.
The only difference I see aside from things that don't affect payload is wheel/tire size. SR5 has 17 inch wheel TRD sport has 18 inch wheel. There is a 300 pound difference in payload, 1400 to 1700.
Is this due to the wheel/tire only? I do not see any other differences in suspension etc...
Can't imagine the axle, frame, is different but?
Thanks for the help

 

Probably suspension and, more likely, the tires. SR/SR5 are the only models on 245s and both have the lower GVWR on the door.

To answer the inevitable, yes, that means if you put the same parts on them they'd functionally be the same and no, that doesn't change the rated payload. You either choose to respect the door sticker or you don't and if you do, get the higher GVWR. The US mostly doesn't give a shit for some stupid reason if you're not a commercial truck.

 

Don't go by the brochure for the payload ratings. Go look at the truck you want ,look on the door jam. There you will find theGVWR. Now go drive across a scale and weigh the truck then you will find your payload. Options,accessories,4x4 and engines all affect payload. I may be wrong but I doubt a Tacoma has a 1700 lb payload.
I looked it up they actually do rate some models at 1700 lb payload lol

 

I did weigh the SR5, took everything out, bare truck 4605 lbs, door panel GVWR 6005. The 1400 lbs appears to be a real number which started me looking into the difference with the Sport.

 

Glad they fixed the payload situation. My 3rd gen is 950 lbs of payload as per door jamb. I've never seen a double cab over 1200 in the 3rd get with a V6.

 

the Sport has stouter suspension for flatter cornering. Maybe that gives it more payload capacity.

 

That is what I was trying to determine between the sport and the sr5. I don't see any difference in the suspension in the specs, only tires and wheels. Specs do not always tell the whole story, as many of us know.
miqie, can you describe what is different about the sport suspension?
What should I look for on my truck? Definitely interested to know if I am on the wrong track.