speedometer gear

I need a new speedometer gear but I can't remember how to do the math to figure out what I need and year one's chart does'nt have the tire size I need :(. If anybody knows how to do the math or just knows what I need I'd be really happy :sunny:. I've cot P265/50 R14 tires and 4.10 gears to an a-833 4-speed. I'd really appreciate any info I can get.