Increase my tire knowledge; floatation tires vs metric

Part of this is a rant.  I very much want pizza cutters on my truck.  Factory tires were 265/75-15 (30.6" diameter and about 10.5" width).  It currently has 31x10.5-15 tires on it.  I want to replace them with the same basic diameter, but I want them skinny.  265mm rubber sucks a lot of gas, isn't as good in the winter, and shortens PS pump life.  About my only choice is to swap wheels to 16" and go 215/85-16, but then they are all E-range.  I don't want E-range on a Fordzda Branger.  At most I want XL or C-range.

Anyway, the real reason I wanted to chat is to discuss the finer points of what separates a floatation tire from P-metric, LT, and other tires.  I know how the letter ranges differ; basically the sidewalls are heavier to hold more pressure and therefore take more weight.

Seems as though floatation tires are more expensive, but what do you get for the extra coin (other than some strange level of credibility in the 4x4 communities)

How does one define a "flotation tire" From my understanding there is P-Metric and Truck ratings (C, D, E etc). 

Now those are generally all marketing and thrown out the window and just look at the load index on the tires IMO. LT tires generally have a little stiffer side wall, but not necessarily. Sometimes they will have an additional ply in the tread, not necessarily. It all comes down to the particular tire and MFG (and if you can find any credible information)

There are a few sizes: P metric, straight metric, LT metric and floatation (like a 31x10.5x15). 

As far as going pizza cutter, the LT215/85R16 is a good option.  Yes, they're all load range E, but as long as you run an appropriate pressure for the weight you're putting on them and don't just pump them up to 80 psi, they should ride fine.  The 225/75R16 load range E M/Ts I keep around for the Jeep ride just fine with around 40 - 45 psi up front and 35 - 40 in the rear.  If anything, they're softer riding than my P255/60R17 106 (non-XL) summer tires. 

You say "flotation tire" my mind goes immediately to super swampers or other mud specific tires. 

Clearly I have more to learn, and since I'm also ranger tire shopping, this will either help or confuse me further. To really throw a wrench into things, I'm looking at using a 17x8 wheel. Not many options in 31"diameter there. 

It sounds like we want different things though. 

In reply to rslifkin :

I agree that I could just run E-range at the 35 psi that the door sticker recommends, but I tried that on a Trailblazer once with less than stellar results.  The sidewalls (since they have to hold up to 80 psi) are notably stiffer and ride did suffer a fair amount.  Maybe it was just the particular tire I chose

Tiresize.com might give you some other ideas for sizes

In reply to ThatsNoUsername :

It does, but it mathematically generates sizes that no one makes.  Like 235/80-16.5

One thing I didn't do was explore bigger wheel sizes.  I wonder if I might find some in 17"  Not sure I want 17s for moment of inertia issues (it is after all a drum rear and only has 160 hp.  I don't want to tank the already boring performance)

In reply to Curtis :

True but maybe you can find something. 

Short of Coker bias ply tires, i cant really think of much off the top of my head

I think the term "flotation tire" is an old colloquial term used for off-road type tires from the '60s.

Basically, any tire that is not P-metric or LT could be considered a flotation tire.

I put 33x12.50x15 all terrains on my Wrangler mainly because LT tires around that same size would be Load Range E and I felt that would be overkill on a 3800lb Wrangler. In addition, the stiff, load bearing sidewalls on the Es would make the ride harsher. My all terrains are rated at Load Range C and fit my needs just fine.

yeah, I was wondering if floatation tires were really constructed any differently any more.  I know back in the bias-ply days they were constructed differently for off-roading so that they could remain undamaged during low-psi sand, mud, and rock crawling duty.

I don't think there's a whole lot different in a radial floatation tire, honestly.  And some are rated for quite a bit of weight, so not necessarily much softer than the higher rated LTs. 

stanger_missle said:

I think the term "flotation tire" is an old colloquial term used for off-road type tires from the '60s.

Basically, any tire that is not P-metric or LT could be considered a flotation tire.

I put 33x12.50x15 all terrains on my Wrangler mainly because LT tires around that same size would be Load Range E and I felt that would be overkill on a 3800lb Wrangler. In addition, the stiff, load bearing sidewalls on the Es would make the ride harsher. My all terrains are rated at Load Range C and fit my needs just fine.

I guess I never heard them called "Floatation tires"

My last truck with inch tires was my F250, 35-12.5R20.  They were load range E and said so right on the sidewall.  The replacement BFG All Terrains I was shopping were 35-12.5R20s also and were also load range E.    Not sure there is a huge difference in construction between the LT Load Range E and the inch measurement or "floatation" tires.  

Here's some hilariously narrow tires for a 15" wheel and they're not even E-rated!

In reply to thatsnowinnebago :

Not a whole lot of options available in 7x15 but the dune buggy crowd loves them. They work great as fronts on a sand rail but they sure kick a lot of sand up onto the driver.

The 7x15 is typically about 29" tall. 

buzzboy said:

In reply to thatsnowinnebago :

Not a whole lot of options available in 7x15 but the dune buggy crowd loves them. They work great as fronts on a sand rail but they sure kick a lot of sand up onto the driver.

Oooo, I was wondering what those were for.

Ok, I used to design passenger car tires for a living, but I can comment on SUV/LT tires. The main difference is the standard they are built to.

What you are calling "flotation" tires are more commonly called LT (Light Truck, aka 3/4, 1-ton, etc pickups, vans) tires and are specified by the american T&RA (Tire and Rim Association). These tires can have one of many multiple ply load ratings (C, D, E, etc.) in the same tire size. The standard also specifies the physical dimensions of the tire and the weight they are supposed to support. Higher load ratings are reached by adding structure to support more air pressure. This is typically done by putting in stronger body plies and/or an additional body ply.

The T&RA also has a separate set of tables of truck sized tires intended for SUVs and 1/2-ton trucks. The size matches, but isn't proceeded by "LT". The physical dimensions are very close, but the tires aren't required to support as much weight at equivalent pressures as LTs. They typically aren't rated to hold the 80-100 psi that LTs are either, also limiting the load they can carry. Thus they don't need the stronger/extra body plies and can sometimes have softer sidewalls.

There is a third standard that is common in the US, commonly known as P-metric, that is published by the ETRTO (European Tire and Rim Technical Organization). The sizes nearly match the non-LT T&RA sizes but are proceeded by a "P". Physical dimensions are very close. Load ratings vary by a few pounds here and there, mostly due to differences in the formulas to calculate them. But they are also intended for SUVs and 1/2-ton trucks.

There are other tire standard organizations out there from places like Japan and Brazil, but T&RA and ETRTO are the two we see in the US.

Between "normal" tires and LT tires there can be a few other differences.

• LT tires can have a slightly different tread pattern and more tread depth.
• The external profile can also differ slightly.
• LT tires are typically stiffer and heavier.
• LT tires can be had in larger and wider sizes than are tabulated in normal car sizes (38", 40", 48", etc) which leads to the 4x4 credibility factor.
• Tread compounds can be different too.

From my perspective there are really only two reasons to pick a LT tire:

1. Desired tire size is not available in normal or P-metric.
2. Needed load capacity cannot be achieved with normal or P-metric tire size.

Make sense (mostly)?

-Sean

Generally, you move two widths for one aspect, and also one aspect for each Indy in wheel. Just rough numbers, not perfectly exact but close. to keep the same size. So if you wanted to go narrower from your 265/75-15, you’d go to a 245/80-15 or a 245/75-15, or a 225/85-15

i think  there are companies making 225/85-16, but that comes to like a 33” tire so probably not what you’re looking for. 

235/85R16 is a thing (32x9.5), but I've never heard of a 225/85.  Basically, the 16" pizza cutters go 215/85 (31x8.5), 235/85 (32x9.5), 255/85 (33x10).  

A tire size 7.00-15 is what people used to use on pickup trucks.  A few places still make them but you would not like them in the offerings available.  https://www.summitracing.com/search/brand/coker-tire/part-type/tires/tire-size/7-00-15

ShawneeCreek said:

Ok, I used to design passenger car tires for a living, but I can comment on SUV/LT tires. The main difference is the standard they are built to.

What you are calling "flotation" tires are more commonly called LT (Light Truck, aka 3/4, 1-ton, etc pickups, vans) tires and are specified by the american T&RA (Tire and Rim Association). These tires can have one of many multiple ply load ratings (C, D, E, etc.) in the same tire size. The standard also specifies the physical dimensions of the tire and the weight they are supposed to support. Higher load ratings are reached by adding structure to support more air pressure. This is typically done by putting in stronger body plies and/or an additional body ply.

The T&RA also has a separate set of tables of truck sized tires intended for SUVs and 1/2-ton trucks. The size matches, but isn't proceeded by "LT". The physical dimensions are very close, but the tires aren't required to support as much weight at equivalent pressures as LTs. They typically aren't rated to hold the 80-100 psi that LTs are either, also limiting the load they can carry. Thus they don't need the stronger/extra body plies and can sometimes have softer sidewalls.

There is a third standard that is common in the US, commonly known as P-metric, that is published by the ETRTO (European Tire and Rim Technical Organization). The sizes nearly match the non-LT T&RA sizes but are proceeded by a "P". Physical dimensions are very close. Load ratings vary by a few pounds here and there, mostly due to differences in the formulas to calculate them. But they are also intended for SUVs and 1/2-ton trucks.

There are other tire standard organizations out there from places like Japan and Brazil, but T&RA and ETRTO are the two we see in the US.

Between "normal" tires and LT tires there can be a few other differences.

• LT tires can have a slightly different tread pattern and more tread depth.
• The external profile can also differ slightly.
• LT tires are typically stiffer and heavier.
• LT tires can be had in larger and wider sizes than are tabulated in normal car sizes (38", 40", 48", etc) which leads to the 4x4 credibility factor.
• Tread compounds can be different too.

From my perspective there are really only two reasons to pick a LT tire:

1. Desired tire size is not available in normal or P-metric.
2. Needed load capacity cannot be achieved with normal or P-metric tire size.

Make sense (mostly)?

-Sean

There is a ton of good info here, thanks.  Most of it resonates with what I have come to know, although in my brain LT tires used metric measurements and "floatation" tires were the ones that used inches.

What I really need is a C-range (or equivalent weight capacity P-metric) in an overall diameter of 31-ish inches that isn't wastefully wide.  An ideal size would be 31x8.5-15 or 215/85-16 (about the same overall profile).  Although plenty of the 215/85s exist, they're all E-range which is ridiculous overkill.

I use this truck for towing up to 5000 lbs, light off-roading including mud and gravel, winter snow.  I also haul some weighty things like engines, loads of lumber or drywall, and of course everyone calls me when they move their fridge or hot tub.  I'm right on the transition where a P-metric passenger tire would be OK, but a C-range LT would be better.  But that point is moot... there are plenty of size selections in 31" diameter in both types of tire... just not skinny choices.

Strizzo said:

 So if you wanted to go narrower from your 265/75-15, you’d go to a 245/80-15 or a 245/75-15, or a 225/85-15

 

Mathematically correct, but no one makes those sizes.  225/85-15 would be lovely.  In fact, what I really want is a 215/90-15, but that is so far off the radar.

Yeah, unfortunately for you, the tire industry has moved away from most load range C tires. They were slow sellers because most people wanted to just go full Monty and get load range E for the extra weight capacity. And as you've discovered, the size you want isn't popular. 

Curveball suggestion, try searching the tire sizes available in Europe. They might have something in the tall and skinny that you're looking for. You'd have to ship them over, but then you might have issues with customs and bring road legal. On second thought, scratch that suggestion. Not really worth the effort.

Second suggestion, you might be able to get a "narrower" tire even within the current 265 size. The 265 refers to the section width (aka, overall width). What you are really looking for is a narrower tread width, which can vary from tire line to tire line. Essentially the tire will be more balloon shaped and less squared off. Get a close look at the specifications for the tires you are looking at.

Thinking about it, a 215/85R16 load range E shouldn't be insanely stiff.  They're only rated for just under 2700 lbs, so even with somewhat stiffer construction than a P tire, they're not a crazy stiff tire with the weight of a pickup on them.  

rslifkin said:

Thinking about it, a 215/85R16 load range E shouldn't be insanely stiff.  They're only rated for just under 2700 lbs, so even with somewhat stiffer construction than a P tire, they're not a crazy stiff tire with the weight of a pickup on them.  

This is the kind of stuff I need to research.  Your logic is sound, but my brain disagrees.

The stiffness of the sidewall for an E-range tire doesn't come from the weight capacity, it comes from the fact that it's designed to hold 80 psi max.  The lower weight capacity is partly due to the reduced volume that skinny tire holds.  It's important to note that a tire's ability to suspend weight has nothing to do with the rubber or the sidewall construction, it has to do with the air pressure.  So, while your logic makes sense, in theory the sidewall of a 215/85-16 E range (with a capacity of 2700) should be identical to a 265/75-16 (with a capacity of let's say 3100).  

This is what I need to research; since the letter range more or less dictates the max psi, are the sidewalls the same across all the sizes and weight capacities (thereby making them all ride just as stiff regardless of actual weight capacity)?