tire size 285/70 or 285/75

[AH64ID]

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.

No

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

And no...


285 is the section width in mm, so 285mm is 11. 22"
70 is the ratio of width to sidewall height. 70% of 285 (11. 22") is 199. 5/7. 85"
Now you take the rim size 17"+(7. 85x2) = 32. 7" tall
So a 285/70/17 mathematically is 32. 7x11. 22 R 17. . but varies based on mfgr. A Toyo AT is 32. 7x11. 5 R17

 

[mberry]

So technically I'm right but you just HAD to throw all that math out there, didn't you AH64ID? I've never been good at math but I understand what you are saying. I didn't know they were a ratio type thing. Thank you for explaining it to me.

 

[AH64ID]

So technically I'm right but you just HAD to throw all that math out there, didn't you AH64ID? I've never been good at math but I understand what you are saying. I didn't know they were a ratio type thing. Thank you for explaining it to me.

Well 70, 75 isnt the width, its the sidewall height. A 285/70 and 285/75 are the same width, but the 75 is 5% taller than the 70%.

Just like a 285/70/17 and a 285/75/16 are the same overall size, but the 17 has a shorter sidewall because of the extra inch of rim.

 

[seafish]

No







And no...





285 is the section width in mm, so 285mm is 11. 22"

70 is the ratio of width to sidewall height. 70% of 285 (11. 22") is 199. 5/7. 85"

Now you take the rim size 17"+(7. 85x2) = 32. 7" tall

So a 285/70/17 mathematically is 32. 7x11. 22 R 17. . but varies based on mfgr. A Toyo AT is 32. 7x11. 5 R17

OOOPS... thanks for the excellent clarification. Also, dealer plugged in 32. 2" into the ecm and lo and behold, the speedo is running exactly right for my 285/75/17 E's. Thanks again!!

 

[RonD]

This one you will have to explain to me, what does the overdrive gear ratio have to do with revs per mile on a tire?,

 

[retirednak]

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

++1 on that. I'll be upgrading come trans time.

 

[AH64ID]

This one you will have to explain to me, what does the overdrive gear ratio have to do with revs per mile on a tire?,

Nothing, other than it effects the rpms the enigne is turning. A taller OD with a taller tire is a much lower rpm than a lower OD with the same tire.

 

[Regcabguy]

I think you really need to use a gps and go for a hundred mile drive to see if the odometer's right. My speedo's hard to nail down. Using a hundred mile distance makes it easy to determine the eror if any. Mine didn't show much in 10-15 miles,but 100 showed a major error.

 

[AH64ID]

I think you really need to use a gps and go for a hundred mile drive to see if the odometer's right. My speedo's hard to nail down. Using a hundred mile distance makes it easy to determine the eror if any. Mine didn't show much in 10-15 miles,but 100 showed a major error.

I agree. . for every mile in 100 its 1%.



I did one with 2 GPS's for 1000 miles, I was only off by 3 miles... so I can live with . 3%

 

[seafish]

I think you really need to use a gps and go for a hundred mile drive to see if the odometer's right. My speedo's hard to nail down. Using a hundred mile distance makes it easy to determine the eror if any. Mine didn't show much in 10-15 miles,but 100 showed a major error.

Dave, you're probably right, but I don't have GPS, that's why I was using the radar sign. Of course, that could also lead to small errors, simply by my not reading the speedo accurately, as I approach the sign. I would use cruise cotrol, but the 2 signs I pass somewhat regularly have approaches on a hill, one uphill and one downhill. Still, I feel fairly confident that I am in ballpark, certainly much closer then where I was after first changing the tire size.

On another note, I am still loving the Toyo AT 285/75/17 E. Last night at VFD training, I found out that the owner of the local garage which sold them to me has since put some on his Chevy and aslo sold a set to the gal who has been wearing out Coopers and Michelins in less then 10k hauling horses up and down these roads several times a day. Looks like I'm starting a trend--:-laf

 

[AH64ID]

Dave, you're probably right, but I don't have GPS, that's why I was using the radar sign. Of course, that could also lead to small errors, simply by my not reading the speedo accurately, as I approach the sign. I would use cruise cotrol, but the 2 signs I pass somewhat regularly have approaches on a hill, one uphill and one downhill. Still, I feel fairly confident that I am in ballpark, certainly much closer then where I was after first changing the tire size.

On another note, I am still loving the Toyo AT 285/75/17 E. Last night at VFD training, I found out that the owner of the local garage which sold them to me has since put some on his Chevy and aslo sold a set to the gal who has been wearing out Coopers and Michelins in less then 10k hauling horses up and down these roads several times a day. Looks like I'm starting a trend--:-laf

I hope you get decent mileage out of them. . Lord knows I cant keep rubber on Toyo's, nor can my dad.

 

[Regcabguy]

Looks like about 35,000 miles out of mine. They've been on two CTD's with cabover campers 24/7. The first 20,000 by my friend with zero rebalance/rotation. 10,000 on mine with three rebalances/rotations. A little harder rubber compound would be nice though. The Dura Grapplers may be next. They felt very safe when we were up Seafish's way with those straight down cliffs.

 

[seafish]

Well 35k would still be better then the 25k I got from my Michelin AT2's, oem size.



Time will tell and then I'll let you guys know.

 

[Blakers]

I have 315/70-17s on my truck and power-wise it loves them. I didn't notice any power loss over the stock tires. I run 70 mph at about 1800 rpm.