tire size 285/70 or 285/75

[Ploughman]

I have done alot of reading recently, but can't seem to solve this. I need new tires to replace the stock michelins. I would like the higher load capacity that the Nitto Dura or Toyo AT's give in the 285 sizes. I tow a 10K lb boat/trailer and also have a slide in camper (lighter bigfoot). I am concerned with the gearing I have and increasing the tire size. I live on the coast of WA and most of my towing is in the 50-65 mph speed. I already find the OD on more than I would like, and as an '05, I only have the tow/haul mode (48re & 3. 73 rear). Its pretty common for me to be putting along at 1500 rpm's and I just can't see lowering that more. Anyone have experience with these sizes and how did it effect the RPM's. Would it be as simple as using the bigger tires and adding a OD lockout to get the RPM's happy? Thanks for the help.

 

[Regcabguy]

I went from 285-70-17's to 285-75-17 Toyo At's and did feel the increase in diameter. I'm just carrying the 2,000# camper but did feel a slight decrease in power. I'm using the Smarty Sr. on sw#1 and need it. The "75"s fill up the wheel well nicer,but the "70"s might preserve your towing ability better. With my g-56 and 3. 73's,I have the equivalent of an auto with 4. 11's. Another size compromise is the 295-70-17 which gives you a litttle wider footprint and a diameter right down the middle @ 33. 3".

 

[goatram]

Ploughman

I to am in the same boat. There is a flash that the dealer can do to provide that true tow haul Capability. I am thinking about the Vision wheels and 19. 5" commercial tires. Increased weight and keeping the right tire ratio are the bennifits. Les Shwab has 4 tires and rims for approx. $2750

 

[Ploughman]

I have considered the 19. 5 route, but I talked to a few people who didn't like the unloaded results. I don't put that many miles on my truck, so the tire life isn't an issue. As you know, it rains here a lot (over 100" each year), and I still want a truck that drives good unloaded. I don't commute with this. It only sees towing, hauling and trail/hunting duty. I really thought the 285 type tires were going to be the ticket for me, but I don't see how to get past the gearing. Maybe a 4. 11 swap?



Regcabguy: I am thinking the 75's will be too much, but how were the 70's? I can get the weight I want with that profile. Would you go back the next time? I find it interesting how many people went to the 75's and now are back on the stock 265 size.

 

[Regcabguy]

I have considered the 19. 5 route, but I talked to a few people who didn't like the unloaded results. I don't put that many miles on my truck, so the tire life isn't an issue. As you know, it rains here a lot (over 100" each year), and I still want a truck that drives good unloaded. I don't commute with this. It only sees towing, hauling and trail/hunting duty. I really thought the 285 type tires were going to be the ticket for me, but I don't see how to get past the gearing. Maybe a 4. 11 swap?



Regcabguy: I am thinking the 75's will be too much, but how were the 70's? I can get the weight I want with that profile. Would you go back the next time? I find it interesting how many people went to the 75's and now are back on the stock 265 size.

The "70" size was ideal for me power and economy-wise but still left me with 2500 rpm@70 mph. :{ It might work out great for you. Without the Smarty,my truck would using fifth a lot more. Huge payload with the "70"s also. 265's would only work in a world of 55 mph with my gearing.

 

[MChrist]

I've got the 285/70/17 Nitto Dura Grapplers with a similar setup. . '06 automatic/3. 73 and I want to say my rpm at 60 mph is 1650 ish. I never had any problems towing heavy with this setup. By heavy, I mean 12,400 lb trailer. Got around 14,000 miles on these tires and still look like new... I would get these again.

 

[AH64ID]

I have considered the 19. 5 route, but I talked to a few people who didn't like the unloaded results. I don't put that many miles on my truck, so the tire life isn't an issue. As you know, it rains here a lot (over 100" each year), and I still want a truck that drives good unloaded. I don't commute with this. It only sees towing, hauling and trail/hunting duty. I really thought the 285 type tires were going to be the ticket for me, but I don't see how to get past the gearing. Maybe a 4. 11 swap?



Regcabguy: I am thinking the 75's will be too much, but how were the 70's? I can get the weight I want with that profile. Would you go back the next time? I find it interesting how many people went to the 75's and now are back on the stock 265 size.

The 70's are rated for 500lbs a tire more than the stock tires. . Thats a lot of weight, over 7K on the rear axle.



But one thing I have never found is anything showing the weight rating of the OEM rims, 3200 is what most guess, so increasing tire ratings doesn't do a lot.



If you really need more than 6500lbs on the rear axle you need 19. 5's or DRW.

 

[Ploughman]

I am much more comfortable running right up to the axle rating than the tires. I just want some "safety" factor in the rubber. I need new tires, so its a good time to improve from stock.

 

[AH64ID]

Goctha. . But the axle rating on a SRW is driven by the tires. The axle for SRW and DRW is the same, and AAM rates them both at over 10K pounds.

I currently have the 285/70's on my truck, and they are a great tire. But I don't think I would go much above 6400lbs on the rear axle based on the wheels.

 

[AWise]

I would get the tire that fits the use/look that you want and if you really need to adjust the gearing then look at a Gear Vendors under/overdrive unit. Hands down the best way to get the proper gearing and drive ability for towing.



Gear Vendors

 

[MChrist]

I thought Gear Vendors was out of business. ?

 

[DennyDay]

Check the NITTO web site, they have a chart for all sizes with weight ratings, revolutions per mile, diameter and about ever other bit of info you would want. The 285/75 X 17E have a capacity of 3970 pounds at 80psig. Just put them on my 06. Haven't towed my trailer yet, but leaving for the east coast next Friday with the trailer.

 

[RonD]

The stock 265-70 tire does 638 revs per mile, the 285-70 will do 617, a 285-75 will be 596. I had a set of 305-70-17 Nitto Terra Grapplers on the truck, I also have a 48RE w/ 373 gears, I found that towing my 14000 5th wheel didn't work well with the gearing, so I went back to a set of Nitto 265-70-17 Dura Grapplers, and everything is fine, with 410 gears the bigger tires I think would have been fine, just my 2 cents, keep the stock tire size, but others will disagree I suspect

 

[AH64ID]

The stock 265-70 tire does 638 revs per mile, the 285-70 will do 617, a 285-75 will be 596. I had a set of 305-70-17 Nitto Terra Grapplers on the truck, I also have a 48RE w/ 373 gears, I found that towing my 14000 5th wheel didn't work well with the gearing, so I went back to a set of Nitto 265-70-17 Dura Grapplers, and everything is fine, with 410 gears the bigger tires I think would have been fine, just my 2 cents, keep the stock tire size, but others will disagree I suspect

You're specs are a little off... you used diameter, not rolling radius(provided by the mfgrs).

Stock is 658 (rolls at 30. 7")
285/70 is 636 (rolls at 31. 7", 3. 34% less than stock)
285/75 is 614 (rolls at 32. 8", 6. 69% less than stock)
305/70/17 is 611 (rolls at 33. 0", 7. 14% less than stock) (Very tall 305 BTW)

There are advantages and disadvantages to taller than stock tires. Since 2200 rpms seems to be the "sweet" spot that allows hills to be pulled in 6th gear and I pull lots of hills in 6th I would have to have tires with a 750 rev/mile size. Since I have 3. 73's and a NV5600. But then at 2500 in 5th I would be at 47. . Stock 2200 rpms was 54 and 74. With my 285/70's its 56 and 76. I am going to a 255/80/17 which will be 57 and 78. . But 2500 rpms (still quiet and cool) will be 64, so I am back to a comfortable rpm for 60-65 towing up hills...

But the 48RE has a . 69 OD, vs my . 74OD. . so thats where you ran into issues.

 

[Regcabguy]

With my GPS,I came up with 33. 3" rolling ht. for 285-75-17 Toyo AT's for everything to jive. My 285-70-17 Toyo AT's required me to adjust Smarty to 31. 0". I would always travel 50 miles to try and average it out and be reasonably accurate. On my last 2300 mile trip the odometer was only off by a few miles from my GPS reading.

 

[seafish]

You're specs are a little off... you used diameter, not rolling radius(provided by the mfgrs).



Stock is 658 (rolls at 30. 7")

285/70 is 636 (rolls at 31. 7", 3. 34% less than stock)

285/75 is 614 (rolls at 32. 8", 6. 69% less than stock)

305/70/17 is 611 (rolls at 33. 0", 7. 14% less than stock) (Very tall 305 BTW)



There are advantages and disadvantages to taller than stock tires. Since 2200 rpms seems to be the "sweet" spot that allows hills to be pulled in 6th gear and I pull lots of hills in 6th I would have to have tires with a 750 rev/mile size. Since I have 3. 73's and a NV5600. But then at 2500 in 5th I would be at 47. . Stock 2200 rpms was 54 and 74. With my 285/70's its 56 and 76. I am going to a 255/80/17 which will be 57 and 78. . But 2500 rpms (still quiet and cool) will be 64, so I am back to a comfortable rpm for 60-65 towing up hills...



But the 48RE has a . 69 OD, vs my . 74OD. . so thats where you ran into issues.

AH64ID,



Can you please tell me what tire diameter I need to have entered in the ecm inorder to achieve an accurate speedo reading. I run the Toyo OC/AT 285/75/17 E. While at the dealership, they inputed the inflated diameter of 33. 8" into the ECM, but my speedo seems to be reading 3 or 4 mph faster then I am actually going according to several careful radar runs. Should they be using the static loaded radius x2 to get a more accurate reading??



TIA



ps--love the tires, quiet and good handling and great looking. I prefer the lower highway rpms, but I only tow 5-7k on occasion. If that ever changes, I may have to rethink tire size.

 

[AH64ID]

AH64ID,



Can you please tell me what tire diameter I need to have entered in the ecm inorder to achieve an accurate speedo reading. I run the Toyo OC/AT 285/75/17 E. While at the dealership, they inputed the inflated diameter of 33. 8" into the ECM, but my speedo seems to be reading 3 or 4 mph faster then I am actually going according to several careful radar runs. Should they be using the static loaded radius x2 to get a more accurate reading??



TIA



ps--love the tires, quiet and good handling and great looking. I prefer the lower highway rpms, but I only tow 5-7k on occasion. If that ever changes, I may have to rethink tire size.

Every truck, for some odd reason, is a little different. But on my truck with the 285/70's I have it set at 31. 45" even thou it calculates to 31. 7", I would have the dealership set your tire size at 32" or 630 rev/mile. This will get you close, and error on the low reading side (better than reading fast).

 

[seafish]

Every truck, for some odd reason, is a little different. But on my truck with the 285/70's I have it set at 31. 45" even thou it calculates to 31. 7", I would have the dealership set your tire size at 32" or 630 rev/mile. This will get you close, and error on the low reading side (better than reading fast).

Thanks for the quick reply... I am heading north today and will give it a shot. There is a radar gun/sign that I can use to check accuracy on the way back... I'll do a few runs to make sure. I'll bet the small diffrences in accuracy have to do with tire pressure and tire wear, BOTH of which will slightly and uniquely affect radius and thus rev/mile.

 

[mberry]

Correct me if I'm wrong, but isn't the 70, 75, whatever number the width of the tire? I thought they were: 265=height 70=width 17=wheel diameter.

 

[seafish]

The first # represents the height of the tire in mm and the second # represents the width of the tire in mm, but as a PERCENTAGE of the height of the tire.



i. e -- 70% or 75% of 285 mm would be ABOUT 200mm or 214mm wide on a 285mm tall tire.



hope that makes sense