True 33s

[Apeachy]

Apologies in advance as there’s probably a thread out there like this already.

I’m looking to upgrade to 33s. I’ve read tires size usually run smaller than listed. Wondering what other people are running for a true 33 inch tire. Do I size up and get 35s? As stated before I read a 35 usually measures a tad over 33 inches.

Pictures with info on builds always appreciated as I’m just a gal trying to figure all this out. I’m currently running 31s on stock suspension on my tj. Yes it rubs a bit- planning on a 3/3.5 inch lift when sizing up tires.

 

[GATORB8]

You're seeing two things, first there are a bunch of idiots who measure tires with the vehicle weight on them. Unless it's overinflated some ungodly amount, no tire regardless of manufacturer will measure full size mounted and on the ground.

Almost all tires end up slightly under advertised diameter mounted/unloaded in the range of 1/2". Some, like BFG KO2s tend to be worse offenders in the larger sizes, but you're probably be looking at an overall range of 1/2" across the market.

Thing is, all of the lift fitment recommendations are using commercially available tire sizes anyway, so a recommended fitment with 33s, isn't necessarily for "true" 33s.

I'd spitball that if you found a metric tire that calcs out to 33.5" or a little more, you'd be as close as you can get.

 

[Strizzo]

"35s" i.e. 315/70-17 or 315/75-16 are typically closer to 34" new, and "33s" i.e. 285/70-17 or 285/75-16 are usually just over 32" to 32.5". This of course depends on brand and model of tire, some manufacturers are closer than others.

If you convert the metric size to inches similar to the us standard, you see where the conversion comes from. 285 in the metric size is the tread width in milimeters, so 285/25.4 11.24"

The 70 in the tire size is the aspect ratio, or the height of the sidewall as a percentage of the treadwitdth - so 70% of 11.24 = 7.85" tall sidewall. So, 2x sidewall plus the wheel size (17") = (7.85 x 2) + 17 = 32.7" so by the "standards" they're not supposed to be a full 33" to begin with.

The same exercise with the 315/70-17 nets a size of 34.36", which is why 315's tend to be 33-34" The 315/70-17 that came on my bronco were almost exactly 33" after about 25k miles.

 

[macleanflood]

My BFG KM3s in 35 are 34.5.

Wife's Mickey Thompson Baja's also 35s are 33.

-Mac

 

[GATORB8]

"35s" i.e. 315/70-17 or 315/75-16 are typically closer to 34" new, and "33s" i.e. 285/70-17 or 285/75-16 are usually just over 32" to 32.5". This of course depends on brand and model of tire, some manufacturers are closer than others.

If you convert the metric size to inches similar to the us standard, you see where the conversion comes from. 285 in the metric size is the tread width in milimeters, so 285/25.4 11.24"

The 70 in the tire size is the aspect ratio, or the height of the sidewall as a percentage of the treadwitdth - so 70% of 11.24 = 7.85" tall sidewall. So, 2x sidewall plus the wheel size (17") = (7.85 x 2) + 17 = 32.7" so by the "standards" they're not supposed to be a full 33" to begin with.

The same exercise with the 315/70-17 nets a size of 34.36", which is why 315's tend to be 33-34" The 315/70-17 that came on my bronco were almost exactly 33" after about 25k miles.

Good point, OP, my comments were related to flotation sizes, like a 33x12.50R15.

If you're going metric, this website has some good converters and charts: https://tiresize.com/chart/

Note, as @Strizzo mentioned, my comments would also generally apply to the calculated diameter of a metric tire, not what Ford/Jeep sells them as on a new vehicle.

 

[machoheadgames]

It doesn't matter, you build it for the nominal. If you are building for "33's", build it for 33's. Don't build it for 33's and then slap on a "small" 35, because it will still be significantly larger than any advertised 33.

Most tires across a specific size will all be very close in size....rarely you will have an outlier from someone like Falken that ends up building their tire larger than everyone else's, but for the most part most tires in a specific size will be about the same and not worth digging deep into the details over.

Most 33's are around 31.5" actual and most 35's are around 33.5" actual.

 

[GoldenGorilla]

Pretty much all 255/85R16s are listed as 33.0" diameter by the mfg where most of the other common "33s" for 15 or 16" rims are listed in the mid to upper 32s. Rim width and tire pressure and a bunch of other factors mattr in final rolling size.

Personally, I don't care. I've had a set of 255/85R16s pizza cutters a long time ago and I do really like that size. I care more about how the tire will perform for the way I use it. The last several tires I've used weren't available in that size and I went with my second choice size 285/75R16.