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· Covered in mud...
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Discussion Starter · #1 ·
Its in Excel format.

I have created tabs with many of the common transmissions and transfer case gear ratios, and tire sizes (you need to enter tires as revs/mile)

Sure, there are online calculators. I like this because I can copy them and make a tab for each vehicle, or possible vehicle configuration.

Just type in your specifics in the white boxes and its all set.

Enjoy! :swampjeep


http://www.lordsofevolution.com/haggar/images/gearchart.xls
 

· give 'er sh*t ay?
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how do you figure out revs/mile?
 

· Covered in mud...
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Discussion Starter · #5 ·
Its always tough to find them for big sizes. Up to 35" I have taken them from manufacturers like BF Goodrich, etc, who publish the sizes.

Above that, the sizes really start getting somewhat different from the sidewalls anyway, so those are pretty close approximations.


If you want to calculate a tire's revs per mile its this:

5280 feet
-----------------
Tire Circumference

Although, tire circumference isn't exactly the right term, since the tire bulges and has a lower effective rolling radius. So you calculate the circumference using the rolling radius.

Example:

If you have a 31" x 10.5" BFG AT on an 8" rim, it has a true rolling radius of 1.245 feet (14.94 inches). So the radius is 1.245 x 2 x 3.14159 = 7.82 feet.

Every rotation, therefore, will drive you forward 7.82 feet.

5280 / 7.82 = 675 rotations per mile.

So, if you went out and measured, say, a 49" IROCK, and it had a loaded radius of 23.5", then it would have a circumference of 12.30 feet. And would have approx 429 revolutions per mile.


:sonicjay:
 

· Me balls are huge
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Here's the formula for using excel to calculate revs per mile:

=20852*((C2/2+((A2/25.4)*B2/100))*2)^(-1.0003)

Copy and paste the above formula into cell D2. Then enter tire width into cell A2, aspect ratio into cell B2, and wheel diameter in cell C2.

In case your real dumb:

Example LT305/70/R16

305 is the tire width in millimeters
70 is the aspect ration (sidewall height is 70% of tire width)
16 is the wheel diameter in inches

Haggar, you might want to add this to your revs per mile tab.
 

· Covered in mud...
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Discussion Starter · #7 ·
FrankNBrew said:
Here's the formula for using excel to calculate revs per mile:

=20852*((C2/2+((A2/25.4)*B2/100))*2)^(-1.0003)

Copy and paste the above formula into cell D2. Then enter tire width into cell A2, aspect ratio into cell B2, and wheel diameter in cell C2.

In case your real dumb:

Example LT305/70/R16

305 is the tire width in millimeters
70 is the aspect ration (sidewall height is 70% of tire width)
16 is the wheel diameter in inches

Haggar, you might want to add this to your revs per mile tab.
I thought about it, but its better to find the true numbers for your tire. It ends up being dependant on the tire, and the variation from true gets statistically larger as the tire diameter gets larger, and varies brand by brand, which is why I left it that way.

For example, when you look at car tires (I use this for looking at car situations, too, for cruising and racing), they are very very close to accurate, usually about 1%-2% smaller than advertised.

Then smallish truck tires like 31s or 265/75R16s have maybe 3-4% smaller.

Once you get up to big sizes, then its all out the window. A 35" SSR is a full 1.5" taller than a 35" Bogger, so you just need to figure whats best for your tire.

That, plus most people aren't running metric tires.
 

· Simplify...
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Haggar said:
Its in Excel format.

I have created tabs with many of the common transmissions and transfer case gear ratios, and tire sizes (you need to enter tires as revs/mile)

Sure, there are online calculators. I like this because I can copy them and make a tab for each vehicle, or possible vehicle configuration.

Just type in your specifics in the white boxes and its all set.

Enjoy! :swampjeep


http://www.lordsofevolution.com/haggar/images/gearchart.xls
Thanks. At first glance, it looks very useful. I'll look at it in more detail over my lunch hour.

FrankNBrew said:
Copy and paste the above formula into cell D2. Then enter tire width into cell A2, aspect ratio into cell B2, and wheel diameter in cell C2.

In case your real dumb:
Nice. :rolleyes: :junk:
 

· Covered in mud...
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Discussion Starter · #9 ·
Thanks!

Feel free to make suggestions/corrections/improvements..


I have some wierdly modified versions for cars where I put in a powerbard, and can see wheel torque output from 5 to 100 mph. More of a carr racing mod, though, and its mostly manually edited..
 
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