what size tires can i get away with on a stock 1998 3/4 suburban 454 4wd Thank you

 

The OEM for your burb was 245/75R-16 which has a diameter of about
30.5". The room you have for larger tires can vary to some extent
with a given vehicle.

You can make a determination on just how much area is available, then,
go to a vendor like Tires at Tire Rack type in a size
which you think will work, and bring up the Specifications for it.

That will show you the tire's diameter, and give you it's revolutions
per mile, where you can see how the increase in size, will effect things
like the accuracy of your speedometer.

Further points...
In viewing the area when the wheels are pointed straight forward, may
not reveal any "closeness" which occurs when they are turned to right
or left lock. You need to know if that will limit you selection, turn um
and get under it where you can really see what's going on.

Also, for the best performance of wider tires, would require a wider
Rim. Had you intended to purchase Rims as well ? If not, not having
a fairly vertical sidewall, can effect the handling of your vehicle.

There are also things like it's Load, Temperature, Traction and Speed Ratings,
which you should consider too.

Good luck.