285/75/16 and 305/75/16 BFG M/T KM2, virtually the same?

[Cañonero]

According with this table at tire rack (click on specs):

BFGoodrich Mud-Terrain T/A KM2

The 285/75/16 and the 305/70/16 has exactly the same diameter, weight and tread width. The section diameter is 12.2 in the 305/70/16 measured in a 9" rim and 11.3 in the 285/75/16 measured in a 8" rim.

Maybe if they were measured in the same rim they would measure the same?

I prefer the 285/75/16 but it has a huge load rate of 3750 lbs at max 80 psi and that leads me to believe the ride would be stiff, and I have enough with my HD springs.

But the 305/70/16, with 2910 lbs at 50 psi. seems like it would be much more comfortable. Maybe if they were inflated at the same pressure they would ride the same, and only the max psi. pressure is what makes the load rate difference?

It's strange though that in the case of the A/T the 305/70/16 has a bigger loading rate than the 285/75/16, it's also heavier and the tread is clearly wider.

 

[cruiserdan]

The height is virtually identical with the 305 having a 20mm wider section.

 

[LukeZero]

I've always thought you should match the air pressure to the load. They list the maximum weight the tire can carry, and the corresponding tire pressure necessary to properly carry that weight.

Ergo- if you're only carrying about half of the total weight the tire is capable of- you would choose a tire pressure that is approximately 1/2 of the maximum.

Maybe I'm wrong- but that's what I've always done and it seems to work.

 

[Ihasfip]

Regardless of max load or PSI, I run 35 PSI on my cruiser on the road. Granted if you have BIAS Swampers or something you may have to play with the pressure to get them to wear decent. Otherwise 35 PSI is a good pressure for most 1/2 ton vehicles. I would only increase the pressure if I was pulling a trailer, and I don't think the Cruiser is capable of pulling a trailer with enough weight to need the max of the tire unless you are running factory size 4 ply rated tires. And like Dan said, 305s and 285 are nearly identical in height. Just wider.

D

 

[Cañonero]

What I don't understand is how they have identical height, weight and specially tread width, but the 305 has a 22 mm wider section.

Maybe because, as it's stated in the tire rack, the 305/70/16 is measured in a 9" rim and the 285/75/16 is measured in a 8" rim?

 

[Cañonero]

I've always thought you should match the air pressure to the load. They list the maximum weight the tire can carry, and the corresponding tire pressure necessary to properly carry that weight.

Ergo- if you're only carrying about half of the total weight the tire is capable of- you would choose a tire pressure that is approximately 1/2 of the maximum.

Maybe I'm wrong- but that's what I've always done and it seems to work.

You got me thinking on that.

Even since the 285/75/16 load rating is rated at 3750 lbs, it needs 80 psi to get that, so at 10 psi it would hold 468,76 lbs.

Then the 305/70/16 load rating is 2910 lbs at 50 psi, so it would hold 582 lbs.

So at the same pressure, the 305/70/16 actually has a higher rating.


Maybe all these calculations are just bull**** and it just doesn't work this way, but it sounds quite right for me.

 

[lispeej]

which one would be better for DD?

 

[Ihasfip]

You got me thinking on that.

Even since the 285/75/16 load rating is rated at 3750 lbs, it needs 80 psi to get that, so at 10 psi it would hold 468,76 lbs.

Then the 305/70/16 load rating is 2910 lbs at 50 psi, so it would hold 582 lbs.

So at the same pressure, the 305/70/16 actually has a higher rating.


Maybe all these calculations are just bull**** and it just doesn't work this way, but it sounds quite right for me.

I don't think it quite works like that. If you ran 10 psi in it on the road it would probably not last very long. It would get too hot and probably blow out. The reason it takes less air pressure to handle the load is due to the increased volume of the tire. Thats how a 44" Super Swamper can carry almost 3,000 lbs at only 30 psi. What I am getting at is I don't think you can take the load capacity and divide it by the PSI to get the load capacity at that given PSI. Does that make since?

D

 

[sandcruiser]

I'll bet it is easier to find a spare for the 285 than the 305

that's worth something

and the 285 will fit better on a stock rim, if that's what you are putting it on.

 

[Cañonero]

I don't think it quite works like that. If you ran 10 psi in it on the road it would probably not last very long. It would get too hot and probably blow out. The reason it takes less air pressure to handle the load is due to the increased volume of the tire. Thats how a 44" Super Swamper can carry almost 3,000 lbs at only 30 psi. What I am getting at is I don't think you can take the load capacity and divide it by the PSI to get the load capacity at that given PSI. Does that make since?

D

Sure you can't run it at 10 psi for long in the street. It was just an example. What you say about air volume is interesting, could we assume then that the ride at let's say 40 psi would be more comfortable on a 305/70/16 than in a 285/75/16, as you are riding over a bigger volume of air?

I'll bet it is easier to find a spare for the 285 than the 305

that's worth something

and the 285 will fit better on a stock rim, if that's what you are putting it on.

Sure the 285 is easier to find, but since they are both the same diameter, I though you could run with three 305/70/16 and one 285/75/16 temporary with no issues.

My rim is a 8x16 steel wheel, so both will fit great.

 

[Ihasfip]

Sure you can't run it at 10 psi for long in the street. It was just an example. What you say about air volume is interesting, could we assume then that the ride at let's say 40 psi would be more comfortable on a 305/70/16 than in a 285/75/16, as you are riding over a bigger volume of air?




Sure the 285 is easier to find, but since they are both the same diameter, I though you could run with three 305/70/16 and one 285/75/16 temporary with no issues.

My rim is a 8x16 steel wheel, so both will fit great.

Hmm, I am not sure about the volume of air thing. 40 psi, is 40 psi. Regardless of the volume. And yea, running a 305 and a 285 is fine.

D

 

[sandcruiser]

if 305/70 and 285/75 are the "same size"
and 285 are cheaper and easier to find
why go 305/70?

I would expect that the 285 would be a better DD as there is less rolling weight involved. Brakes last longer, ride should be smoother as you have a lower unsprung weight, and drivetrain components should also last longer. You should also see better in-town mileage for the lower weight, and possibly a very small increase in freeway mileage for the narrower profile tire (less wind resistance)

 

[dnp]

According with this table at tire rack (click on specs):

BFGoodrich Mud-Terrain T/A KM2

The 285/75/16 and the 305/70/16 has exactly the same diameter, weight and tread width. The section diameter is 12.2 in the 305/70/16 measured in a 9" rim and 11.3 in the 285/75/16 measured in a 8" rim.

Maybe if they were measured in the same rim they would measure the same?

I prefer the 285/75/16 but it has a huge load rate of 3750 lbs at max 80 psi and that leads me to believe the ride would be stiff, and I have enough with my HD springs.

But the 305/70/16, with 2910 lbs at 50 psi. seems like it would be much more comfortable. Maybe if they were inflated at the same pressure they would ride the same, and only the max psi. pressure is what makes the load rate difference?

It's strange though that in the case of the A/T the 305/70/16 has a bigger loading rate than the 285/75/16, it's also heavier and the tread is clearly wider.

All things being equal, in my personal opinion, the width of the 305's look SOOOOOOOO much better! (and, arguably, have better traction due to the tread width) I run 305's on one of mine, and I wouldn't consider going back with anything narrower........just one person's opinion....

 

[Ihasfip]

if 305/70 and 285/75 are the "same size"
and 285 are cheaper and easier to find
why go 305/70?

They are the same overall diameter. But the 305s are wider. I like the look of the 305's as well. In my opinion ( and I sell tires every day) 20 mm difference in width isn't going to make a noticeable difference in gas mileage, ride quality or anything else for that mater. The added benefit would be looks, and possibly better traction due to the slightly wider footprint.

D

 

[Cañonero]

Remember in this particular case the 305/70/16 and the 285/75/16 have the same weight, diameter and footprint, just the load rate and the section width change (measured in different rims).

I prefer the 285, but I'd go with the 305 for a more comfortable ride as the loading rate much lower, but I don't know if there would be a difference with equal pressures.

 

[sandcruiser]

I'm dubious- how can the 305 be wider, yet weigh the same?
Regardless, for my driving style, wider isn't more attractive. I look forward to getting 255/85s on there.

So my vote stays w/ the 285s. But it is probably a pretty academic "debate" as the size differences aren't very large in any event.

 

[Pathfinder]

This should help you see how they differ in size. Diameter is the same just the tire width is slightly larger.

Tire size calculator

Good luck

 

[Jack G. Nichols]

On RV and truck tires (and maybe these?) tire manufacturers have charts (or formulas?) that state the load carrying capacity is correlated to air pressure. Therefore, weigh each corner independently, and you will then be able to find the proper inflation pressure for the temperature expected.

I'm just guessing here. I bet some tire guys can clear this up.

Jack Nichols, '93 LC with Michelin 285s at 35 PSI (305s next time)