Construction Differences Between Metric and Floatation Sized LT Tires

OCD Overland

Explorer
This is probably a dumb question, but why do manufacturers offer conventional LT tire sizes that are only slightly off from their LT-metric counterparts?

For example, if I want 35" BFG All-Terrain KO2's for a 17" rim, they offer both an LT315/70/R17/E 121 S and also an LT35x12.5R17/E 121 R.

The obvious difference between the two is the speed rating, R vs S, but they're also sized ever so slightly differently (a tenth of an inch here or there) and the conventional tire is also a bit heavier. But both are LT's, the load rating is the same, there's nothing to indicate any construction or tread difference, and they cost roughly the same.

These two tires must be different for a reason, but I have no idea why. I can only see that the conventionally sized tires in general have the lower speed rating and seem to be slightly heavier.

So is there some general rule that I don't know about for the difference between tires that are sized conventionally vs metric? Why would I choose one over the other? I can only assume that it has something to do with the sidewall construction, but I can't find anything that would indicate if that's so or what the difference would be. I just feel like this must be some basic bit of car info that everyone must know but me, because I can't find it explained anywhere.
 
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ExplorerTom

Explorer
I thought metric is conventional. :coffee:
And the one main country to still use "conventional" is still the only country to fly their flag on the moon.

So using your math, 98% of the world has 2 things in common: use of the metric system and never putting one of their countrymen on a foreign world. That's good company right there.

And that's without getting political.
 

rayra

Expedition Leader
And the one main country to still use "conventional" is still the only country to fly their flag on the moon.

So using your math, 98% of the world has 2 things in common: use of the metric system and never putting one of their countrymen on a foreign world. That's good company right there.

And that's without getting political.
lol we PLOWED a Mars Surveyor mission right into the planet instead of a grazing orbit, because someone on the team muddled a metric to standard conversion.


The OP's answer is that huge amounts of tires are still sold in the American market, and despite decades of attempts the metric system still hasn't taken root here. So they're still made that way. I'm sure sometime in the near future the tire companies will nut up and go all metric.
 

drewactual

Adventurer
the answer to most of this breed of question: lawyers...

but in the end, it's just a ti-yer (from the by-gawd south, yo) and that's all... and if'n ya want to be persnickety 'bout it, ain't a one of them that is what they say they is- it's about the silliest way to get 'somewhat close' when choosing a size, and that is using whatever metric you want- inches, mm's, hands, or even that magical measuring standard young men use when they start measuring at their ******** hole.... if that were the case, my 37" tires which are actually 36.2 and less than 35.5 under compression would be no less than 60"ers...
 

OCD Overland

Explorer
Well, it has to be more than a labeling thing, otherwise they'd just take the same tire and put a different label on it. These two tires are literally just a tenth of an inch different, and I doubt they'd make an entirely different mould for a tenth of an inch, especially when that mould is still half an inch smaller than what they're labeling it as.

My guess is that there is some construction difference between the two that they just aren't explaining. I mean, one is S rated and the other R, so there's clearly a difference. But is the R rated tire tougher, more pliable maybe? What's the advantage to the R rated tire if they're both the same price?

I've asked this question to BFG directly - we'll see what they say but I assume it will be a few days before I hear back.
 

I Leak Oil

Expedition Leader
I suspect that as fewer vehicles can use a 15" or 16" wheel, you'll see fewer tires advertised in conventional inch sizes.

Oh, and a difference in compound can cause them to differentiate essentially identically constructed tires.
 

hoser

Explorer
These two tires must be different for a reason, but I have no idea why. I can only see that the conventionally sized tires in general have the lower speed rating and seem to be slightly heavier.
I suspect the difference is mostly in the marketing. The 315/70R17 w/ "S" speed rating is an OE size for the Ford Raptor and ? whatever else. Many big tire chain will specify a replacement tire of equal or greater load capacity and speed rating. They won't go through the trouble of converting Floatation sizes to Metric. The 35x12.5R17 is a popular size for those modifying their trucks (the other market).

I prefer when the tire company just states both sizes, when there is an equivalent.

IMG_0813.jpg
 

RedF

Adventurer
And the one main country to still use "conventional" is still the only country to fly their flag on the moon.

So using your math, 98% of the world has 2 things in common: use of the metric system and never putting one of their countrymen on a foreign world. That's good company right there.

And that's without getting political.
Even the US has essentially converted to metric tire sizing. Is there even a vehicle sold in the US that isn't OEM equipped with a metric size tire? The most recent one I can think of would have been Dakotas and Durangos. There will always be a niche market for flotation size tires, just like 15" wheels, but those markets will continue to shrink.
 

DanR7985

Observer
I prefer standard sizings because they are so much easier to understand. 33x10.5x17 Very simply 33" tall, 10.5" wide, 17" rim. If metric followed the same format it wouldn't bother me. Instead you have to take percentages and all that crap.

The width number doesn't bother me because 265 is a width without doing anything special. It's the height that is dumb I think. It would be much simpler to do something like 265/838/17 or something like that, or switch it around to like 838/265/17.

I think back to Robin Williams' skit on golf when he is talking about the creation and how it was just to screw with people playing. I wonder sometimes if whoever thought up the idea of metric sizing just wanted to screw with people as well

For what it's worth I do think we should switch the metric sizes in general in the U.S. but that is neither here nor there.
 

OCD Overland

Explorer
Well, I don't know how helpful BFG is going to be with this. Here is the response I got back from them...

Sizing for light truck tires takes the performance requirements of the vehicle and the tires into account. Light truck tires have evolved along with the expanded applications of trucks and vans that have grown to be multi-purpose vehicles that we use for work, recreation, or as passenger vehicles. This tire is used more for use on highways and off-road, depending on the tire.

The metric sizing is considered a Light Truck High Flotation type tire. Light truck high flotation tires have evolved as lower aspect ratio tires became more popular on light trucks. The combination of lower aspect ratios and high flotation yielded better traction on sand and soft soil found in off-road situations. Most people who use the High Flotation tires generally may have customized suspension systems.

The sizing and construction of the tires along with the intended use are much different from each other. You may also consult your tire dealer about which is best for your purposes.
OK, well they at least are saying that there is a difference between the two, but the problem is that what they're saying doesn't make much sense. First off, the tires I asked about are the same size/aspect ratio, so that undermines basically everything they said. And secondly, the thing that kicked this off in my mind is when I noticed that Ford/Foutz Motorsports swapped out the metric tires that they've been showing on the new Raptor for conventional ones when they raced at Mint last week. Strange behavior indeed if the metric sized tire is supposed to be better off road. Maybe the person who answered just has it backwards. I'll write back to see if I can't get a clarification or more info.
 
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