I have a triple axle backhoe trailer with 7,000 lb axles. The tires on it are 235 85 16 E rated for 3042 lbs each. It hauls my skid steer and my old smaller backhoe just fine but I just bought a larger backhoe. I loaded it up and ran it across the scales and the trailer axle group weighed 20,740lb with 3020 lb on the tongue. This is right at the limit for the axels and over the current tire ratings. I see they make some 235 85 16 G rated at around 3900 lb which would cover me or should I just bite the bullet and buy some 17.5" wheels and put some 215 75 17.5s on it rated at 4805lb each? If I move the stop on the front I think I can move the backhoe forward another 18" or so which would take some weight off the tires and add it to the tongue but I still will need stouter tires.
If you can find 8 hole 17.5 rims, that would be my vote. I have a buddy that only runs those on his trailers. He has 10 hole, 8,000 lb axles. You'd be surprised at how much easier they pull. If you're ready to upgrade, go for it. Oh yeah, the tires will last longer, too.
Just make sure you have enough spacing between the axles so the tires don't rub each other.
I think the 215 17.5's are actually a tiny bit smaller than the 16's so no rubbing issues I don't think.
I switched from 16' to 17.5 on two 10 ton tags this spring. And it was money well spent! My vote goes for 17.5
All the 17.5 wheels I have seen are made for 8000lb. axles. That being said I put them on my triple axle about four years ago. They have holes for 5/8 studs and the 7000 axles have half inch. I found pipe the right size and made shims the width of the wheels to center the wheels. The wheels are also for flat face lug nuts. For this I went to speedway motors. They have 1 inch lug nuts for half inch studs for stock cars. Turned the lug nuts around and have absolutely no problems with this setup. I've worn the first set of tires out so that tells you how many miles they have run. Best thing I ever did to the trailer. Maybe a little red neck, huh?
I agree, opt for 17.5 tires when you can. Much better than any 16" tire available.
Go 17.5 never look back. If they are newer 7k axles the 5/8 studs should go right in. Shoulder size the same