An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio

[Rebelguy2020]

No need to do calculations.

Tire Size Comparison

Tire size comparison the easy way. Use our tire size comparison calculator to compare diameter, width, sidewall, circumference and revolutions per mile.

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I’ve been retired for a few weeks now, 38 years as a machinist, I was relaxing having my coffee with Irish cream of course, and had the idea to do the calculations for the difference between the wheels, not very complicated for me, I worked to the thousands of an inch for years.

I’ve seen tire size charts before but never came across the revolutions per miles, good to know. Thank you.

I know I’m off the subject, my main hobby is wood working, kitchen cabinets are the biggest projects that I make, I don’t use that particle board crap, I use 3/4” veneered plywood, birch, oak, aspen (poplar) or maple to make the cabinet frames, they are assembled using biscuits, not a single screw.
The cupboard doors and drawer fronts are made of solid wood cut on my sawmill that I build several years ago.

Before and after pictures of poplar cupboards I made for the tiny house we bought for my mom to live. I also made the birch butcher block counter top. I also did the door in the picture. The poplar came from my yard, I have 10 acres, half of it is natural forest, the other half is lawn.

 

[ferraiolo1]

This thread keeps getting better and better!


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[Louhound88]

No way would 35's cause your speedometer to be off by 12 mph...more like 3-4 mph. Was that a typo?

My stock tires measured out to 31" tall, new tires are 34.75" tall on the truck. Stock tires are not 32.1" while mounted. And I've had 35x12.5 tires measure out to around 34 or little more, but my tires now measure out to 34.75".

At 55mph on the speedometer I was actually traveling 61. It isn't linear, and continues to spread the faster you'd go. I'm sure there is some error in google gps speed, but this is using my phone's gps while navigating to a location with google maps. Clear, open skies. I've used phone gps for rough speed calculations for years and it works well enough to keep me from getting tickets.

 

[Scram1500]

Mine was off by 2-3 mph at 70 by just going up a diameter from 275/65 to 275/70

 

[AngelPhoenix]

This thread keeps getting better and better!


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Scroll: Smaller tires!
Scroll: 392!
Scroll: 321!
Scroll: Check out my cabinets
Scroll: 392!
Scroll: Bigger ti...wait what...?

 

[c3k]

Tire size and miles per hour...

Doing the straight math, tire profile ratio * width, plus wheel diameter to determing circumference, is close...but not right.

There's a reason why manufacturers include revs per mile on their tire spec charts. Tires are squishy, and their "dynamic" circumference is different than their static size would suggest.

I used (on 3 tire changes) the listed revs per mile, and my speedo was spot on with my GPS speed. FWIW.

 

[Mountain Whiskey]

Scroll: 321!
Scroll: 392!
Scroll: Bigger tires!
Scroll: Smaller tires!
Scroll: 392!
Scroll: 321!
Scroll: Check out my cabinets
Scroll: 392!
Scroll: Bigger ti...wait what...?

Oh, oh, let's add to it. What will fall faster, a 1 pound lead ball or a 100 pound aluminum ball.

Please, supergeeks and eggheads, leave aerodynamics out of it for a short drop.

 

[Eighty]

Oh, oh, let's add to it. What will fall faster, a 1 pound lead ball or a 100 pound aluminum ball.

Please, supergeeks and eggheads, leave aerodynamics out of it for a short drop.

What gear ratio does the lead ball have? 3.92 or 3.21?

 

[Mountain Whiskey]

What gear ratio does the lead ball have? 3.92 or 3.21?

You got the catch!

They will fall equal because the 1 pound has the 3:21 gears and the ball that is 100x heavier has the 3:92 gears to handle the load.

Once again, PROOF, 3:92 is superior!

 

[Scram1500]

Oh, oh, let's add to it. What will fall faster, a 1 pound lead ball or a 100 pound aluminum ball.

Please, supergeeks and eggheads, leave aerodynamics out of it for a short drop.

Trick question! They both fall at the same rate, on earth that would be approximately 9.81 meters per second squared

 

[Eighty]

Trick question! They both fall at the same rate, on earth that would be approximately 9.81 meters per second squared

That doesn't happen in the US of A. Things accelerate at 32 feet per sec^2 here. Take your metric units and go somewhere else (anywhere else, really - they all use metric!)

 

[Mountain Whiskey]

But if they have 3:92 gears the load would accelerate faster giving it the lead.

 

[Scram1500]

That doesn't happen in the US of A. Things accelerate at 32 feet per sec^2 here. Take your metric units and go somewhere else (anywhere else, really - they all use metric!)

All the metric nuts and bolts on this thing has me confused which country this is, nevermind all the socialism talk

 

[Mountain Whiskey]

All the metric nuts and bolts on this thing has me confused which country this is, nevermind all the socialism talk

Well, in case you wondered, Mexico.

 

[Scram1500]

Well, in case you wondered, Mexico.

Es de puta madre! Time to bust out the tequila

 

[Mountain Whiskey]

Yes, the extent of my Spanish "dos cervezas por favor. muy frío." In a heavy southern drawl.

 

[KWKSLVR]

I'm confused at why almost an entire week has gone by since we've discussed why 3.92 is clearly the only choice for those that have made a lifestyle out of overcompensating for personal deficiencies?

 

[AngelPhoenix]

I'm confused at why almost an entire week has gone by since we've discussed why 3.92 is clearly the only choice for those that have made a lifestyle out of overcompensating for personal deficiencies?

Dude said, "Kick the hornet's nest? Nah, how about flag down the Independence Day aliens..."

 

[theblet]

3.21 ftw

 

[Eighty]

I have the correct answer. Everyone has it wrong - 3.55 is the best. Has to be coupled to a Hellcat engine on 35” tires though.