Bigger Tires?

Thanks, Pianotuna, good reply. It brings up a thought. Why not just change the gearing in the rear dif?
Larger tires are less efficient, but the drop in rpm overcomes this, but keeping small tires and changing the gearing will drop the rpm and keep the tires small…
I actually want larger tires to "look" better also, so may stick with tire changes. Ground clearance is a plus.
I have had oversize tires on my truck before and the mileage dropped off considerably, but that engine was having to work.
Interesting about the 215/85-16. I have heard that more narrow tires are more efficient than wide tires, so even a large diameter tire that is narrow will be better than a wide tire of smaller diameter. Any experience anyone?

That Michelin document address above is for an old version - 2007.

This is the 2015 version, that for instance, includes data on their MS2 tires:

https://www.michelinb2b.com/wps/b2bcontent/PDF/Truck_Tire_Data_Book.pdf

Andy, Look at this they have a chart showing with and diameter.
http://www.michelintruck.com/assets/pdf/Truck_Tire_Data_Book_Jan2007.pdf
I don't see that much difference between 225/75/16 and up to 265/75/16 The 265s are about 1 inch wider and 2.5 inches taller. The benefit of the bigger tire is the load capacity goes up to 3415lbs at 80 psi.
Bill

My class C came with Load Range D tires and the recommended inflation was right at the upper limit for these tires. When I replaced my tires I went to LR E tires and increased the inflation by 5 psi. I don't really know if it improved my gas mileage or not, but I feel better with the LR E tires.

Hi Phil,

I could not do that size exchange--I was overweight on the driver's rear.

Grit dog my tires absolutely required a different offset. There are "cheaters" that can be used--but they are not recommended for heavy vehicles.

There is a very easy way to go up in tire size slightly for slightly better fuel economy and more ground clearance without changing your rims and without worries of the dually sidewalls rubbing.

Go "up" to 215/85R16 tires of the same Load Rating as your current 225/75R16 tires. I ran stock 225/75R16 Load Range E tires on our Class C motorhome for several years before switching to 215/85R16 Load Range E tires around 3 years ago. The 215 tire actually has about a 1.2 inch larger diameter than a 225 tire, so all gears are just a bit "taller", for better mileage. Load Range E is Load Range E, so both tires can carry identical maximum loads. A 1.2 inch larger diameter provides 0.6 inches higher road clearance for the entire vehicle, including all suspension and drive components and all coach components. The 215 tire is slightly narrower than the 225 tire, so spacing between dually sidewalls is wider to better guarantee no sidewall rubbing and there is another advantage - more air flow between the dually sidewalls for improved cooling of the tires in hot weather travel. Also, another advantage seldom talked about is - at any given loading - reduced tire tread wear when tire diameters are increased.

Of course I had to buy seven (7) tires at replacement time (a new spare, too) to change to the larger diameter tires, but I need only buy six(6) from now on. I now use Michelin LTX M&S2 215/85R16 tires.

Any loss of power from the larger diameter is insignificant, since we have an E450 chassis under our small (24 foot) motorhome instead of an E350 chassis. The E450 has more pulling power due to it's lower rear differential gear ratio, slow larger diameter tires have no effect that we can feel when pulling grades. The speedometer now has about a 1.5 MPH under-speed reading error at cruising speeds, but that is of no concern to us.

I have run over-stock-diameter tires on some of my vehicles for years with no negative effects whatsoever.

Not going to hurt a bit to put 235/85 or 245/75 on. They are not much wider so rear tire spacing shouldn't be an issue, but measure first.
As long as they don't rub at the bottom you're fine.
Not certain what cooling has to do with it. If there's an air gap between your tires your fine.

The engine will produce less power at a lower rpm, but this 460 will chug up almost any hill in over-drive, so I have some power to spare.
Cooling is something I have not thought about, has anyone had real experience with this?
Pianotuna, what vehicle and engine did you put your bigger tires on?

Hi,

I bought new wheels and went to 235/85r16. It gave me about 1 mpg improvement. It improved ground clearance as well. In addition the tires have more carrying capacity.

Assuming you are speaking of a class C RV, you need consider the spacing between the rear dual tires. Cooling is a factor and bigger tires may decrease that cooling... might even cause other problems.