Odd Measurement!

[Oneshotlucky]

Okay so I got BFG 34x10.5x17 tires. Manufacturer says it’s 33.5 in diameter. Just measured the tire with a level and it’s 32 3/16??? Truck isn’t loaded with anything tire pressure is about 37psi. Am I missing something??

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[WILDHOBO]

The measurement under vehicle weight is significantly less than not. Mine are over 3/4” smaller under the weight of the vehicle.

 

[Rahkmalla]

33.5 is a measurement by the manufacturer of the tire inflated under no load. Some mnfrs (it is suspected not proven) will even inflate their tires to the maximum PSI to get their measurement.

The second you put weight on a tire it's going to get shorter.

It is exceedingly rare to put a tire on a truck under it's weight, and get the measurement the mnfr got.

Why is this allowed and not deceptive marketing practices? Well for starters, who'd to say which vehicle you're going to put a tire on and how much it weighs? On a lighter vehicle the tire will be under less load and therefore taller.

Just gotta learn which brands have a tendency to run smaller. BFG for example definitely runs smaller, as even their 37s fit in the spare tire carrier (obviously not under load) when most other 37s will not fit there.

 

[WILDHOBO]

33.5 is a measurement by the manufacturer of the tire inflated under no load. Some mnfrs (it is suspected not proven) will even inflate their tires to the maximum PSI to get their measurement.

The second you put weight on a tire it's going to get shorter.

It is exceedingly rare to put a tire on a truck under it's weight, and get the measurement the mnfr got.

Why is this allowed and not deceptive marketing practices? Well for starters, who'd to say which vehicle you're going to put a tire on and how much it weighs? On a lighter vehicle the tire will be under less load and therefore taller.

Just gotta lean which brands have a tendency to run smaller. BFG for example definitely runs smaller, as even their 37s fit in the spare tire carrier (obviously not under load) when most other 37s will not fit there.

Mickey Thomson 37’s run bigger than most at 36.8 under no load. Mine are 36 even under the weight of my JTR. They do fit in the spare well as well btw, fully inflated. People tend to think only small 37’s fit, but I’ve proven that to not be the case. I do have a bent rear track bar from clayton for full articulation, but it fit with the oem one as well when not off road.

 

[Rahkmalla]

Mickey Thomson 37’s run bigger than most at 36.8 under no load. Mine are 36 even under the weight of my JTR. They do fit in the spare well as well btw, fully inflated. People tend to think only small 37’s fit, but I’ve proven that to not be the case. I do have a bent rear track bar from clayton for full articulation, but it fit with the oem one as well when not off road.

That's good to know, that you for the correction!

 

[WILDHOBO]

That's good to know, that you for the correction!

Any time. I hate to see people move towards alternate mounting before trying to get it to fit. It’s snug in there, but I didn’t even need to remove the heat shield.

 

[redriderjf87]

For what it's worth my stock 32's come out as almost exactly 31" under load at ~38 psi.

Some data collection of this by brand or tire under gladiator load might be handy to make as a thread I think (if not already started)

 

[ShadowsPapa]

That's good to know, that you for the correction!

Well, you did use words like exceedingly rare, and didn't say things like always or never........ so it was still accurate

Okay so I got BFG 34x10.5x17 tires. Manufacturer says it’s 33.5 in diameter. Just measured the tire with a level and it’s 32 3/16??? Truck isn’t loaded with anything tire pressure is about 37psi. Am I missing something??

Welcome to tires.
Have you bought any lumber?
Bought any 3/4" plywood or 2x4s?

There's also a difference between running diameter and measured diameter.......... when I changed the tire size settings in my truck to make the speedometer/ODOmeter match up to reality, I had to compensate for reality - rolling diameter. And that will even vary by air pressure, which varies by air temperature.

Rubicon JTs come with what everyone calls a "33' and yet they measure 32.8" diameter - less when installed and loaded. Yet everyone calls them a 33. What a rip-off. Subway got sued for their foot long sandwiches measuring less than a full 12" - and yet, here we are.
Overland comes with what everyone calls 32" tires - but they are 32.2", a bit less installed and loaded.
There's just about 1/2" difference between the advertised diameters - so when does it stop being a 32 and start being a 33? When is a 33 really a 34 or a 34 really a 33?
Sometimes I swear, tire numbers, rattling off "I got me a set of 60s today" as if bragging about some certain measurement......... get the tires you like in the size you like or NEED or that makes sense for you and don't sweat it.
Sometimes I wonder what we're really comparing LOL They're bloody stupid tires.

Anyway, the charts and advertised numbers are strictly for comparison purposes, nothing more. How many more revolutions per mile with this tire vs my originals, that sort of thing - or hey, I want a tire that's the same diameter as my originals - how do i compare and know what I'm getting? By those charts and numbers.

 

[Rusty PW]

BFG's run small to what on the sidewall. 35's are like 34's, etc.

 

[Oneshotlucky]

Well, you did use words like exceedingly rare, and didn't say things like always or never........ so it was still accurate




Welcome to tires.
Have you bought any lumber?
Bought any 3/4" plywood or 2x4s?

There's also a difference between running diameter and measured diameter.......... when I changed the tire size settings in my truck to make the speedometer/ODOmeter match up to reality, I had to compensate for reality - rolling diameter. And that will even vary by air pressure, which varies by air temperature.

Rubicon JTs come with what everyone calls a "33' and yet they measure 32.8" diameter - less when installed and loaded. Yet everyone calls them a 33. What a rip-off. Subway got sued for their foot long sandwiches measuring less than a full 12" - and yet, here we are.
Overland comes with what everyone calls 32" tires - but they are 32.2", a bit less installed and loaded.
There's just about 1/2" difference between the advertised diameters - so when does it stop being a 32 and start being a 33? When is a 33 really a 34 or a 34 really a 33?
Sometimes I swear, tire numbers, rattling off "I got me a set of 60s today" as if bragging about some certain measurement......... get the tires you like in the size you like or NEED or that makes sense for you and don't sweat it.
Sometimes I wonder what we're really comparing LOL They're bloody stupid tires.

Anyway, the charts and advertised numbers are strictly for comparison purposes, nothing more. How many more revolutions per mile with this tire vs my originals, that sort of thing - or hey, I want a tire that's the same diameter as my originals - how do i compare and know what I'm getting? By those charts and numbers.

Okay! So I entered 32.42 to set tire size with the Tazer. I’m 1 mph faster on gps than the dash. To tweak it do I go up or down in tire size settings to get it to match?

 

[ShadowsPapa]

Okay! So I entered 32.42 to set tire size with the Tazer. I’m 1 mph faster on gps than the dash. To tweak it do I go up or down in tire size settings to get it to match?

Increase tire size in the settings - then the truck will think for each revolution of the tire you are covering more ground in the same timeframe.

I prefer the odometer method because it's more accurate. I compare the trip meter/odometer to what the GPS says I have covered. If the GPS says I've covered 17 miles exactly, the trip meter on the truck should read the same. Speedometers only read in even miles per hour.

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