is your blade tension tight enough?
there are two way to track your saw so that it runs parallel to your fence.
1. set you blade up so it is running like you want- then take a scrap of plywood say 8' square- draw a pencil line parallel to one good edge. start cutting the ply on the line- when about half way - with a nice straight cut- hold the wood in position- i uded to clamp it in position- then adjust the fence to match the good side of the ply.
2.keep adjusting your tracking until it is cutting // to the fence- sometimes the blade may have to be a bit off center on the top tire to achieve this.
the way guides should be set up- this is how we do it on bigger commercial type band resaws- top guides can be bearings- bottom guides blocks- reason being that if sawdust drops down between the bearings and the blade- it can start to damage things. your inside guide( throat side) should be set to be just touching the blade- now on a lot of commercial saws- these are cooled- heat being the no.1 enemy of bandsaw blades. i dont use coolant- so i have the guide just touching ever so slightly- kind of like a "cow catcher" this does 2 things- it scrapes the blade clean- and in turn keeps the tires clean of any pitchy oily material you might be cutting- but also prevents blade deviation- outside guides can be say, a business card thickness clearance.
on big re -saws they allow only 3/16 deflection between guides, on the blade- pushing it with your finger from the outside towards the throat.
if it is always veering, is the set on the teeth equal- has the blade on the one side run up against any metal etc- like the throat on the table- that will reduce set on one side- and cause the blade to veer in that direction.- or the teeth could be contacting with the steel part of the wheel( either wheel) changing the set- some wheels can have a little metal lip on either side- to keep the tire from running off.
best thing we ever did with a fabric cutting bandsaw we used, was took the silly rubber tyres off- sent the wheels in, had them vulcanize the rubber on, and crown it accordingly.- ran that saw for 20 years in a factory never a days problem- 10 years later the new owners are still running it daily- no problems.
hope that helps some!