The number is a ratio of width and sidewall height. Hit google for "tire size calculator" and you can plug in the metric size to get LT sizes....

I'm planning on H2 take-offs when I find a set for a decent price

 

So the 75 means an actual taller tire than the 70 ?

 

with everything else being equal yes... but if you change the width of the tire around, that can change... if you had a 285/75 and a 305/70, they are virtually identical in height. now take a 235/85 and a 265/75 the are nearly identical in height. same goes for a 255/85 and 285/75, nearly identical in height the second number [usually from 35-85] is the aspect ratio. so basically the sidewall height compared to the width of the tire.. i didn't say anything about rim sizes as that changes things too...

ie,
285/75/16 = ±32.8" tall [done with the math, not specific tire measuring]
325/50/20 = ±32.8" tall
275/60/20 = ±32.9" tall

0.100" isn't much to worry about with tire size differential as a new tire will have like 0.500" difference in height compared to a worn out tire...

 

I just put Pro Comp MTs 35x12.50x17s w/ 17x9 Chrome Moto Metal 951s, I had the 315s (I think I'm the only one that thinks the 315s are cheap chevy takeoff junk) but any way if you really go offroad the 315s will rub even w/2" level kit. The 35s are much better tires w/ better looks, they will rub as well. If you dont use your truck offroad dont sweat it

 

I am running goodyear 305/70/17 mtr's on stock 17" wheels and no rubbing. According to goodyear they are 34" in diameter. I spent alot of time trying to find the biggest tire that would not rub and so far no rubbing. They are great tires but a bit spendy.

 

I put 315/70R17 on my stock truck. I loved the look but hated loosing 6th gear! I lost at least 2 MPG empty. I hooked up the 5er (11,000#s) and was not real happy. I mainly drove in 5th. It did well at 55 MPH turning 2,300 RPM but the highest I saw my fuel economy for the trip was 9.9 MPG. I was getting around 11 MPG with the 265s. The truck would pull 6th but my EGTs went up (and stayed up) too high with the lowered RPM. I was afraid to go fast enough to get the 6th gear RPM up to lower the EGTs. The sidewall flex of the 315s at 50 PSI was not real comfortable either. I ended up taking them back and putting 285/70R17 on. I am hoping when I pull the 5er in a couple weeks it does better. The 285s look nearly as good and I am more pleased with the drivability now that the 315s are gone. OH, the 315s also rubbed on the control arm at full turn. Doesn't seem to be a problem except for parking lots and backing the 5er into tight spots.

 

what is the largest tire you can put on dually with out the back tires rubbing and what brand is a good tire.i changed my truck into a dually and need to find tires fast.thanks

 

what about a 305/50/20 rim and tire? more of a low profile sidewall correct? anyone running these? any rubbing? what about a 315/50/20?

thanks

 

I am running 305/50/20's on a 20x10 wheel and it does not rub at all and we did not have to trim the truck. Check my pics.
Here is a wheel/tire size comparater so you can input your stock wheels/tires and various new wheels/tires and backspacing to see what will fit.
http://www.bigcustomwheels.com/rt_specs.jsp

 

305s will be perfect but they will be expensive. Lots of us run 315s because they were fairly cheap a couple of years ago. They are readily available on e-bay as H2 takeoffs and you can get some at a decent rate used. It's pretty hard to find new ones right now. Everyplace I looked had them on backorder!! I just got some H2 takeoffs and have my alloys/315s in the classifieds..

 

I have had 315, 305, and 295 on my truck.i changed my truck to a dually and i am wondering if 265 80 17 will work because that way my gear ratio will be the same as stock.also i have a set of 305 mtr s with 2000 miles on them that going into the classifieds and a truck bed and wheels but back to the question if 265 will work or not and can i get a small spacer to go in there i know duallies have 235 and they are 10 inches wide and 265 are 10.43 will they work?

 

budsowner, I was told before the265's will work but I still don't know first hand. I did see a landscraper with a stock dually running around here with GY MTR's. Looked good but, once again, was not able to verify tire size or ask about any issues.

 

I ended up getting 235 80 17 whats comes on them but i did get cooper tires i will post pics soon of the truck the wheels will be here this week.thanks for the help.

 

Thanks budsowner. What Coopers did you get? Can't wait to see how they look.

 

Heres the fronts.