I own a 2001 F-250 4x4 with limited slip which came from Uncle Ford with 265 75R16 tires. The spare is also the same size. I am looking at new tire time and have thought of upgrading the size to 285 75R16s, however I have heard of problems...

First, I tow a 8,000 lb travel trailer with this truck. Therefore, it gets to work a little. When I asked about the change in size, the tire guy recommended against it if I were going to keep my original spare (265). His thoughts were I might damage my limited slip if I had to put the spare on the rear, especially while towing.

Any thoughts or experiences with this? I am not going to spend another $150-$180 just to replace an already perfectly good (and unused) spare.

Edmo

 

If you did have a flat on the rear you could swap one from the front to the back and put the spare on the front. As long as you don't lock in the front I believe you would be safe until you got the right size. Or you could always buy a used tire for a spare.

 

yea, what Menroid said, it may take more work when you get a flat but you wouldn't have to buy an new spare. thats what i do.

 

Thanks for the reply...

According to the table on tirerack.com, the 2 tires have the following specs:

265s / 31.8" diameter / 655 revolutions per mile
285s / 33" diameter / 631 revolutions per mile

Bottom line: The 285s spin 24 fewer times per mile and if my math serves me, the fewer spins are as a result of having a 7.5" larger circumference. When you look at the small difference in height (diameter) it doesn't seem like much, however that 1.2" difference changes the revs quite a bit.

I think I will get the 285s, keep my 265 spare and hope for my flats to occur on the front when not towing!

Any other thoughts out there??

Edmo

 

Going to a LT285/75R16 it will probably be an 8ply tire. Compared to the 10plies you have on there now. Those extra 2 plies help dissapate heat while towing. Not to mention your truck is already grossly over weight as it is. You could possibly build up to much heat on the tire under load and have a blow out forcing you to use your smaller spare. which would blow out your rearend limited slip if driven on over time. THe 285 does have a higher load carrying cappacity but that doesn't mean a whole lot as it would heat up faster at that capacity then a 10 ply tire.

THe other thing to think of is, how wide are your rims. I think the stock rim on your truck is 7 inches wide. The 285 is recommended for use on an 8 inch rim. Putting it on a smaller rim will cause a balloning affect. And basically you would be riding on the center part of the tread. THat means a loss of traction(compare to mounting it on recommended rim width) and a focus of the heat on to a smaller area of the tire.
Also the tire will change your gearing, transmission shift points, odometer, speedometer, and ABS braking system. Which are all calibrated to the original tire size diameter, and rear end gear.

 

I have a formula to calculate your new effective gear ratio if your interested. It can also tell you the percent of change that that tire will affect everything else

 

My 10 Ply "E" range 265s have a weight capacity of 3,415 lbs while the 8 ply 285s "D" range tires are rated at 3,305 lbs. Not that significant of a loss.

The 285s list a suggested rim size range of 7.5" - 9" with 8" recommended... You are correct about my rims, they are 7". If I have a flat in the rear, although a huge pain, I could rotate the spare to the front and move one of my front 285s to the rear.

One question. How is my truck, "...grossly over weight as it is."?

What would be my new rear gearing with the bigger 285s? I have the 4.30 rear gears now.

Edmo

 

Your gearing would remain 4.30, your speedo would read about 4% lower than your actual speed (631/655 = 0.963) At an indicated 65 you'd be doing 67.5.

Personally, I would be very concerned about the undersized rims. Running a tire too wide for the rim can create a lot of additional sidewall flex which with that much load is not a good idea.

 

Your apprent gear ratio will change. While the number of ring and pinion gears obviously wont, the larger tires will cause the truck to behave as if you have changed them. Since you are already at 4.30, the effect should be manageable in terms of decreased power off the line, and as long as you arent a lead foot, mpgs will go up.

I would stick with the 265s anyway.

 

I meant that the gvw of the newer fords is in the neighbor hood of 10,000lbs. Thats no light weight. The formula for the effective gear ratio is:
Current ratio x (Revs per mile of new tire/ Revs per mile of original tire)= New effective gear ratio
So yours would be:
4.30631/655)= 4.14 new effective ratio.

That means your new tires size will fill like you were driving with something in the neigbor hood of a 4.14 rearend with the stock tires.
And remember that its not just the max load of the tire but the number of plies or load range of the tire that will determine how well the do under load

 

Thanks for the replies...

Most F-250s come off the line with 8 ply "D" range tires, however the dealer I bought mine from in Alaska orders them with the heavy-duty 10 ply tire package.

My truck's max gross weight is 8,800 lbs, so even "D" range 265s at a max weight of 3,000 lbs for each tire have me covered. The 3,415 lb weight rating of the "E" 265s give me 1,660 lbs of extra capacity and are really overkill (in a good way).

Bottom line: I think the 285s look better in a 4x4 wheel well... they just aren't as strong as the 265s I have on the truck now, and they will give me problems if I have a flat with my 265 sized spare.

Still pondering...

Edmo

 

I've never seen one of the newer F-250's stock with a D tire. Look in your door plate to see whaat the original equipment is. I've worked on many of these and never seen on with D's and no manual I have says D's came as an option. Check your GVW in the door plate along with the tire specs. The 8800lbs would be right if you had a regular cab I think?

 

About spending the extra money on the spare....I have 285s and I just went and bought a decent used spare tire of the same size. I dont know how far you would have to drive on the spare but if it isnt too far that would get you to the tire shop...even with a load, if it were a decent tire
Just a thought
P.S. I think my spare cost 75 dollars and it was like 60% tread
got a great deal