31" and 32" tire size question

[hulk311]

Just to make sure:

265/70R16 = 31" tire

265/75R16 = 32" tire

Correct?

 

[IanB]

It depends on the specific tire to some degree, but when I was looking at Duratracs:

265/70R16 = 30.7" tire

265/75R16 = 31.7" tire

 

[Pikeman]

Hulk- you are correct.

IAN- even though the measurement is not exact it is still considered to be equivalant size. Also if you look at a 31x10.50 tire you'll find those measurements are also not exact. It is called nominal sizing.

 

[hulk311]

Ok, thanks, I'm thinking of downsizing from my 255/85/16 Coopers to 32" tires.

 

[Pikeman]

Which Coopers are you running the AT or MT and why are you wanting to downsize? I am thinking of going the 255/85 route and heard that the Cooper ST is the only AT in that size. Would like a quick review if it is the AT so I can decide.

 

[MTDewX8]

dang choices. lol

:snacker:

 

[hulk311]

Which Coopers are you running the AT or MT and why are you wanting to downsize? I am thinking of going the 255/85 route and heard that the Cooper ST is the only AT in that size. Would like a quick review if it is the AT so I can decide.

The tires I own are

DISCOVERER S/T LT
LT255/85R16 DISCOVR S/T D OWL.

I'm downsizing because 95% of my driving is on the highway and I've only been offroading a couple of times.

 

[KAILUAZ]

Newb question, but whats the attraction to the 255/85? I've seen several people running them and often wondered.
Thanks

 

[Pikeman]

Here is a little bit copiend from a link on Expeditionportal. Why skinny tires - Expedition Portal Forum

Less rotating mass- Easier to start and stop
Less reciprocating mass- Easier to dampen
Less wind resistance- Better economy and range
Less rolling resistance- Better economy and range
Easier to fit a taller/narrower tire with less lift
Lighter spare
Lighter tire
Lighter wheel
Less unsprung weight
Less weight and leverage on steering components, bearings, etc.

In terrain:
1. Less frontal resistance in mud and sand. Where is most of the increased contact patch (for flotation) gained? In the length, not the width. Tall and narrow allows for more length and greater deformation with less resistance.

It is as simple as understanding the coefficient of friction (COF), which is (Ff = Cf x Fv).

Ff= Friction Force
Cf= Coefficient of Friction
Fv= Force Vertical

As you make a tire wider, you reduce the Fv over a larger area, but gain Cf. As you make a tire narrower, you increase the Fv, but reduce the area of contact, which lowers the Cf. It is proportional, though there are times when the material interaction (lets say a drag tire on concrete) favors Cf, but those conditions rarely exist on the trail, on a perfectly flat surface. So, if a wide and narrow tires benefits with relationship to Cf and Fv are proportional, than the decision must be made on other factors, like weight, resistance, etc., as listed above.

Now of course, there are limits at both ends of the spectrum. Too narrow of a tire, and the torque applied to the surface, even with extremely high Fv (which a super narrow tire would have), would exceed the rubbers ability to resist tearing. Literally, burning rubber.

It is all a balance, with tires for most of the trucks we drive being ideal in the 9-11" wide range.

Big, fat tires are only for show trucks and tundra buggies. An expedition vehicle has an emphasis on simplicity, economy, durability and safety, none of which a 35x14.5 will give you. . .

 

[blcktpgsr]

I was just about to blurt exactly all that just on top of my head but you beat me to it, just kidding...Good to know Pikeman

 

[Pikeman]

I want to make it clear, I did not write or come up with the previous post. I simply had read it previously, remembered where it was and then copied and pasted.

 

[KAILUAZ]

Cool, thanks for the info. I kind of like the tall skinny tire look myself.

 

[Jared Pabis]

Just to make sure:

265/70R16 = 31" tire

265/75R16 = 32" tire

Correct?

I think the tire manufacturers websites are really helpful. They usually provide the inflated diameter, the tire width, contact width, and tread depth.

265/75/16's can vary over half an inch in inflated diameter, and about 1/4 of an inch in width. I have Yokohama Geolander AT/S's in 265/75/16 and they are 31.9 in O.D. With stock suspension they rubbed pretty bad...and they still rub after a 2.25 inch lift. I've seen other 265/75/16's on stock 4Runners that had no rubbing issues, so it goes to show what half an inch in diameter can do.

 

[hulk311]

Guys, I'm selling these tires if anyone is interested in the tall tire look that's great for offroading.

http://www.toyota-4runner.org/class...oper-discoverer-s-t-lt-lt255-85r16-tires.html

 

[octanejunkie]

Here is a little bit copiend from a link on Expeditionportal. Why skinny tires - Expedition Portal Forum

Less rotating mass- Easier to start and stop
Less reciprocating mass- Easier to dampen
Less wind resistance- Better economy and range
Less rolling resistance- Better economy and range
Easier to fit a taller/narrower tire with less lift
Lighter spare
Lighter tire
Lighter wheel
Less unsprung weight
Less weight and leverage on steering components, bearings, etc.

In terrain:
1. Less frontal resistance in mud and sand. Where is most of the increased contact patch (for flotation) gained? In the length, not the width. Tall and narrow allows for more length and greater deformation with less resistance.

It is as simple as understanding the coefficient of friction (COF), which is (Ff = Cf x Fv).

Ff= Friction Force
Cf= Coefficient of Friction
Fv= Force Vertical

As you make a tire wider, you reduce the Fv over a larger area, but gain Cf. As you make a tire narrower, you increase the Fv, but reduce the area of contact, which lowers the Cf. It is proportional, though there are times when the material interaction (lets say a drag tire on concrete) favors Cf, but those conditions rarely exist on the trail, on a perfectly flat surface. So, if a wide and narrow tires benefits with relationship to Cf and Fv are proportional, than the decision must be made on other factors, like weight, resistance, etc., as listed above.

Now of course, there are limits at both ends of the spectrum. Too narrow of a tire, and the torque applied to the surface, even with extremely high Fv (which a super narrow tire would have), would exceed the rubbers ability to resist tearing. Literally, burning rubber.

It is all a balance, with tires for most of the trucks we drive being ideal in the 9-11" wide range.

Big, fat tires are only for show trucks and tundra buggies. An expedition vehicle has an emphasis on simplicity, economy, durability and safety, none of which a 35x14.5 will give you. . .

I've read that article too, you should post the pros and cons, for serious wheelers going up rock ladders a pizza cutter tire has a smaller contact patch. Maybe we are not "serious wheelers" but we are not mud whompers either. The best solution is one that lends itself to the driving you will be regularly doing that is in your budget - meaning if you go through 2 sets of tires a year because of how you use them, then you have to have budget for that.

Good link, thanks for posting it in this convo

 

[Mark_BC]

Here is a little bit copiend from a link on Expeditionportal. Why skinny tires - Expedition Portal Forum

Less rotating mass- Easier to start and stop
Less reciprocating mass- Easier to dampen
Less wind resistance- Better economy and range
Less rolling resistance- Better economy and range
Easier to fit a taller/narrower tire with less lift
Lighter spare
Lighter tire
Lighter wheel
Less unsprung weight
Less weight and leverage on steering components, bearings, etc.

In terrain:
1. Less frontal resistance in mud and sand. Where is most of the increased contact patch (for flotation) gained? In the length, not the width. Tall and narrow allows for more length and greater deformation with less resistance.

It is as simple as understanding the coefficient of friction (COF), which is (Ff = Cf x Fv).

Ff= Friction Force
Cf= Coefficient of Friction
Fv= Force Vertical

As you make a tire wider, you reduce the Fv over a larger area, but gain Cf. As you make a tire narrower, you increase the Fv, but reduce the area of contact, which lowers the Cf. It is proportional, though there are times when the material interaction (lets say a drag tire on concrete) favors Cf, but those conditions rarely exist on the trail, on a perfectly flat surface. So, if a wide and narrow tires benefits with relationship to Cf and Fv are proportional, than the decision must be made on other factors, like weight, resistance, etc., as listed above.

Now of course, there are limits at both ends of the spectrum. Too narrow of a tire, and the torque applied to the surface, even with extremely high Fv (which a super narrow tire would have), would exceed the rubbers ability to resist tearing. Literally, burning rubber.

It is all a balance, with tires for most of the trucks we drive being ideal in the 9-11" wide range.

Big, fat tires are only for show trucks and tundra buggies. An expedition vehicle has an emphasis on simplicity, economy, durability and safety, none of which a 35x14.5 will give you. . .

I don't think I buy that. I'm into mountain biking and fat biking and for riding on sand, fat tires make a huge difference. I currently have 4.8 inch wide tires on. According to this I could just as easily ride with 2" wide tires which is BS.

 

[cccolin]

I don't think I buy that. I'm into mountain biking and fat biking and for riding on sand, fat tires make a huge difference. I currently have 4.8 inch wide tires on. According to this I could just as easily ride with 2" wide tires which is BS.

I'm gonna guess that the difference between 2 and 4.8 inches for the weight of a human and bicycle is a different ball game than the difference between 9-11 and 14 inches for truck mass, when it comes to sand. For one thing the bike tire width difference is 1:2.4, while for trucks it's about 1:1.55 for 9 vs 14, and 1:1.2 for 11 vs 14. Put another way, the wider of the bike tires you are comparing is 120% wider than the smaller. The wider of the truck tires compared is, at most, 55% wider.