False tire sizes

[Little diesel]

I ran Interco MS-16's on my Ram...things shook like a bitch. Good customer service though.

That was same problem I heard back in 90s

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[Deleted member 28696]

My 37”x20 Nitto Trail Graplers are actually a tad over 36”.

 

[RVcruzer]

Speedometers are calibrated by the circumference of the tire. Normally the circumference of the tire is 3.1416 (Pi) times the diameter. The problem is that tires aren't solid and air pressure changes affect the diameter (height) of the tire when the truck is just sitting there. For rock rolling with lower pressure the height is what counts but if you are calibrating your speedometer you need to know the true diameter.

The way to determine what diameter to use when calibrating a speedometer just put a chalk mark on your tire at the bottom, dead center where it meets the road. Then put a piece of blue tape or whatever on the pavement. Roll (or drive) the truck forward until the tire makes a complete 360 degree rotation with your chalk mark once again at dead center bottom. Put another piece of tape on the pavement at that point. Then grab a tape measure and measure the distance between the two tape marks. Divide by 3.14.16 and you'll find the true rolling diameter that you can use for calibrating your speedometer.

 

[Wolf Island Diver]

Pipe! Lumber! Tires! Bags of Potato Chips! Push-Up Bras.

THE WORLD IS A LIE!!

<foams at mouth>

 

[ShadowsPapa]

Speedometers are calibrated by the circumference of the tire. Normally the circumference of the tire is 3.1416 (Pi) times the diameter. The problem is that tires aren't solid and air pressure changes affect the diameter (height) of the tire when the truck is just sitting there. For rock rolling with lower pressure the height is what counts but if you are calibrating your speedometer you need to know the true diameter.

The way to determine what diameter to use when calibrating a speedometer just put a chalk mark on your tire at the bottom, dead center where it meets the road. Then put a piece of blue tape or whatever on the pavement. Roll (or drive) the truck forward until the tire makes a complete 360 degree rotation with your chalk mark once again at dead center bottom. Put another piece of tape on the pavement at that point. Then grab a tape measure and measure the distance between the two tape marks. Divide by 3.14.16 and you'll find the true rolling diameter that you can use for calibrating your speedometer.

Interesting you mention rolling diameter - that's how ITPMS works - with no in-tire sensor. It measured the differences in the tire's rotations compared to the other tires.

 

[ShadowsPapa]

Pipe! Lumber! Tires! Bags of Potato Chips! Push-Up Bras.

THE WORLD IS A LIE!!

<foams at mouth>

Welcome to the matrix - which obviously needs to be recalibrated.

 

[bgenlvtex]

Super common, good luck with your campaign...

 

[Wolf Island Diver]

Not to hijack the thread <he says as he hijacks the thread> but how do people actually aquire tires to measure in the first place? I called BFG to inquire about KM3s and the lady on the other end of the phone just started crying. If I hadn’t taken an arrow to the knee I’d be off on a nationwide quest to actually prove the existence of 37” plus tires. I’m starting to think they are a myth from the realm of YouTube influencers and don’t really exist. And Quadratec is like the Charlie from the movie Snatch with the tire back order ETAs right now.

 

[Andyz]

Ok just measured my 35x12.50 17 dick cepek extr country and they are 33.5 with 40lbs air pressure and less than 500 miles. So contact manufacturer and going to complain and will start a petition for recall or whatever. They should be sued for false advertisin. I did not pay $305 for a stupid 33.5, I paid that much for a 35. Now I know from reading these threads on this site they are other brands doing same and some brands are true to size. I say petition them to do the right thing. This is robbery and deceitful. Maybe someone on here can inform me to make me feel better. I would like to be wrong and or something, I would like to tire that we ain’t getting rubbed over by tire folks, when they more off of racing and off road vehicles

Ok just measured my 35x12.50 17 dick cepek extr country and they are 33.5 with 40lbs air pressure and less than 500 miles. So contact manufacturer and going to complain and will start a petition for recall or whatever. They should be sued for false advertisin. I did not pay $305 for a stupid 33.5, I paid that much for a 35. Now I know from reading these threads on this site they are other brands doing same and some brands are true to size. I say petition them to do the right thing. This is robbery and deceitful. Maybe someone on here can inform me to make me feel better. I would like to be wrong and or something, I would like to tire that we ain’t getting rubbed over by tire folks, when they more off of racing and off road vehicles

OK being an ex Tire guys, first off tires from the manufacture have never been sold as outside diameter, so 315/70-17 are 70% of 315mm x 2, plus 17", do the math and it come out as 34.36". Yes annoying if the sell them as 35's but that's just marketing, rounding up and making a differential between 31, 33, 35. Always best to check manufacturers specs if exact hight is super important to you. Use the Rim/percentage of width (aspect ratio) calculation as that is how they are manufactured, not matter what is on the sidewall....and yes unloaded or off vehicle.

 

[jorbasaurus]

PSI against times the square inches of that foot print for each tire, added together, will give you the weight of your truck.

I’ve sat here way too long trying to come up with a clever Jeep PEMDAS joke. So I’m just gonna say thanks for the cool info and move on lol.

 

[DBravo]

Did you not plug in the tire size you were looking to buy into the numerous tire size and comparison calculators and charts on the tire vendor sites? Several good ones even allow you to compare two tires, give the revs per mile, diameter, width and much more.
Been that way for YEARS.
ACCORDING TO THE CHARTS at tirerack, discounttires and other places -
The so-called 32" tire on the Overland is actually 32.2"
The so-called 33" tire o the Rubicon is actually 32.8" so in reality there's only .6" difference between the two.
That's according to the actual tire makers specs.

I'd rather see us sue the lumber sellers for selling us 2x4s that are only 1.5 x 3.5" and 3/4" plywood that's not 3/4" thick by any stretch.

Pretty neat tire size comparison calculator here: https://tiresize.com/comparison/

 

[mtudb24]

only certain manufactures are true to size. Grabber ATx are a true 35 and 37'. Mine measure 35.0 mounted on quadratech 8.5" wide rims running 35psi

 

[Tuggernuts]

only certain manufactures are true to size. Grabber ATx are a true 35 and 37'. Mine measure 35.0 mounted on quadratech 8.5" wide rims running 35psi

I really wanted those tires. America’s Tire said they were two months out.

 

[AstroZombie]

It's like buying a quad or a dirt bike. It's not really a 700cc engine. It's just between 600-700

 

[mtudb24]

I really wanted those tires. America’s Tire said they were two months out.

Damn that sucks. When I got mine last September, they were in stock at Discount tire the next day.

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