You will need a blade that is a little wider than tire tracks when at an angle . Much also depends on the amount and type of snow your dealing with . Heavy deep snow can be an issue .
Take the outer width of rear tires and multiply by 1.15. That means the blade will cover your tracks when angled 30 degrees. Get a blade that is that width or slightly wider. I am sure a 5' blade would do it on a BX.
Agree with above.
5' blade does fine on my BX1500. It's only limiting factors that I've run into are
1) Weight - I should have passed on the cheap blade that came with the tractor. It rides up in packed tire tracks and such. My BX will lift plenty more.
2) Ground clearance. I can only blade as much snow as will pass under the tractor so I end up pushing with my bucket ~8" off the ground like a "first pass" and the rear blade handles the remaining 8". When things get packed and icy, she'll power through in a straight line with bucket in float on the ground in combination with the rear blade, however little steering is available.
Hopefully that provides a little more insight for you. I'm not sure what my blade weighs and certainly you don't want too much, but mine is cheap and lighter than most.
I agree on that "cheap blade that came with the tractor" comment. I made that mistake, being a newby at the time. Had to trade it in for a heavier model, and lost some money in the trade.
Rear blades are designed for slow speed use. Snow blades have trip mechanisms and shoes to prevent catching ruts where you can get up some speed to make up for the low weight. Not to say many don't plow with rear blades its just from personal experience with catching a rut with a 7ft blade. Thanks to a cast Iron old massey, just the blade snapped at the hinge. I have also pretzeled the lower link arm on my B3200 pushing gravel and catching a rut. This winter (well sometime this winter) I am going to look into attaching an ATV manual angle snow blade to my bucket.
get a blade that a little wider that the back wheels .
For a lot of angle grading to the side on a long lane then a wider blade may be what you want so the snow will be dumped past the wheels.
if you do need to widen a blade after you get it . you can up widen it with 45 degree wings to widen it and hold more snow. to determined just how big a blade you can handle you can attach 2x6 across the blade until you get the width that works best or is too wide to bull
as well you may want to put wheels or skids to keep it from digging in to the ground. (2) 6" steel swivel dolly wheels bolted to the back of the blade should do this.
If you bolt plastic from plastic barrel it will keep the snow from sticking to the blade