"Skinny" tires on a Full-Size?

[Hopeless Diamond]

The diameter of a tire is a product of the whole tire size number, not just the first part of it. the first 3 digits (i.e. 255) tells you the section width of the tire. The second part is the aspect ratio (85), i.e. how tall the sidewall is, as a percentage of the section width. This, in combination with the wheel diameter will give you the overall diameter.

255/85/16 = 10" width, 8.5" sidewall (x 2), 16" wheel = 33" tall tire
255/80/17 = 10" width, 8" sidewall (x 2), 17" wheel = 33" tall tire

There's always some minor variations due to manufacturer, tread style, tolerances, etc.

Flotation Tires size, give you the diameter and width as part of the number - i.e 35x12.50R/xx will be real close to 35" tall and 12.50" wide no matter the wheel size

 

[Skwerly]

I see! Good stuff. Thanks!

 

[freedomrider]

I've recently went through tire sizing boot camp so I thought I'd add a little to Hopeless Diamond's explanation for anybody still scratching their head in confusion.

The first two numbers in the sequence are in metric units (mm) and the last number is in inches. There are roughly 25.4 mm per inch so for a 255/85/16 tire the measurements are:

Tire width: (255 mm)/(25.4 mm/inch) = 10.04 inches
Sidewall height: (10.04 inches)(0.85) = 8.53 inches
Tire diameter: (8.53 inches)(2) + (16 inches) = 33.06 inches

Hope that helps clarify more than it obfuscates.

(edited to correct mm to inch conversion factor as pointed out by 98GP)

The diameter of a tire is a product of the whole tire size number, not just the first part of it. the first 3 digits (i.e. 255) tells you the section width of the tire. The second part is the aspect ratio (85), i.e. how tall the sidewall is, as a percentage of the section width. This, in combination with the wheel diameter will give you the overall diameter.

255/85/16 = 10" width, 8.5" sidewall (x 2), 16" wheel = 33" tall tire
255/80/17 = 10" width, 8" sidewall (x 2), 17" wheel = 33" tall tire

There's always some minor variations due to manufacturer, tread style, tolerances, etc.

Flotation Tires size, give you the diameter and width as part of the number - i.e 35x12.50R/xx will be real close to 35" tall and 12.50" wide no matter the wheel size

 

[98GP]

25.4mm = 1 inch

 

[freedomrider]

25.4mm = 1 inch

Thanks for the correction. I've been using the wrong conversion factor for years (note to self: the old brain's memory is not as reliable as it thinks it is).

 

[98GP]

No problem...
I had to google it to make sure I was thinking straight and not some funny rounding thing like π (pi)

 

[BCHauler]

I needed to see this...I've been debating these 2 sizes too. On a 01 f350.

Sorry, I didn't see this earlier.

Sorry, I also have a pic with the truck with the camper on it and the 255's but I can't find it.

 

[Skwerly]

I've recently went through tire sizing boot camp so I thought I'd add a little to Hopeless Diamond's explanation for anybody still scratching their head in confusion.

The first two numbers in the sequence are in metric units (mm) and the last number is in inches. There are roughly 25.4 mm per inch so for a 255/85/16 tire the measurements are:

Tire width: (255 mm)/(25.4 mm/inch) = 10.04 inches
Sidewall height: (10.04 inches)(0.85) = 8.53 inches
Tire diameter: (8.53 inches)(2) + (16 inches) = 33.06 inches

Hope that helps clarify more than it obfuscates.

(edited to correct mm to inch conversion factor as pointed out by 98GP)

Hey, that's great! Perfect explanation. Thank you so much! I gotta say, this tire stuff is a bit enthralling for the nerdy side of me.

 

[freedomrider]

Hey, that's great! Perfect explanation. Thank you so much! I gotta say, this tire stuff is a bit enthralling for the nerdy side of me.

Glad I could help.

Just got the word that my new truck that I ordered back in December (F-350 Lariat FX4 6.2L SRW CC SB ) AND it's accompanying camper (Northstar 850SC) both came in today. And just in a nick of time for an upcoming camping trip. I'm one stoked puppy! :victory:

 

[Hopeless Diamond]

Wow, how did you pull that delivery timing off? I would assume the gasser is the same, I have a F-350 Lariat FX4 6.7L D SRW extended cab SB, best road trip vehicle I've ever had! I had somebody ask me how I liked it one time - told them I hated it, couldn't get enough to time to enjoy driving it

 

[freedomrider]

Wow, how did you pull that delivery timing off?

As Joe Walsh sings "I'm just lucky that way"

Actually so many other things have been going bad it was only a matter of time before something worked out right. I'm happy to leave defeats in the rear view mirror and celebrate the victories.

I would assume the gasser is the same, I have a F-350 Lariat FX4 6.7L D SRW extended cab SB, best road trip vehicle I've ever had! I had somebody ask me how I liked it one time - told them I hated it, couldn't get enough to time to enjoy driving it

Thanks for the endorsement. I test drove the diesel and really liked it but decided on the gasser due to initial cost and personal preference.

 

[Townsend]

Glad I could help.

Just got the word that my new truck that I ordered back in December (F-350 Lariat FX4 6.2L SRW CC SB ) AND it's accompanying camper (Northstar 850SC) both came in today. And just in a nick of time for an upcoming camping trip. I'm one stoked puppy! :victory:

We need pictures!

 

[Hopeless Diamond]

PS you will need to get shocks, the "off road" Rancho ones that come with FX4 package are worse than garbage. You'll be lucky if they last 10k on smooth pavement

 

[freedomrider]

We need pictures!

Dropped off the truck this morning to get it set up for the camper. I'll get some pics on it's maiden voyage next week and post in the "Full Size Pics" thread.

PS you will need to get shocks, the "off road" Rancho ones that come with FX4 package are worse than garbage. You'll be lucky if they last 10k on smooth pavement

Thanks for the advice. My wrenching knowledge is pretty weak but I'm anxious to learn as much as a late bloomer can. I'll probably start a dedicated thread to post all of my 4x4 newb questions. But I'll start with a few here that I've been pondering since I started reading this thread:

What constitutes a "skinny tall tire"? The skinny part is sort of straightforward but what's the cutoff? 265? 255? And does it depend on the vehicle (e.g., is a skinny tire for a F-550 necessarily skinny on a F-150?). As far as the tall part, is it strictly a matter of the outer diameter or does the sidewall height also matter (e.g., a 35" tire on a 16" rim versus a 35" tire on a 18" rim). The tires on my new truck are 275/70/18. I suspect they're neither tall nor skinny for the vehicle they're on. Apologies in advance if these seem to be dumb questions.

 

[TooTall'sTruck]

The only dumb question is the one that is asked twice.

The "70" of your new tire is the % of width that is in the sidewall. SO I would say that most tires that are "80" % of the tread width would constitute as tall. But it is all relative to your application. Some of the heavy hauler class 8 trucks run lowboy steer tires for about a week then yank them back off because there is so much more rolling resistance with that wide of a tire. Tall and skinny has a diminishing point of returns, but I would say around 35" tall and less than the standard 12.5", my mind recalls that for the fullsize trucks a 35/12.5-17 is about the stock-ish limit...so a 35/10.5-16 would be taller and skinnier