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Old 03-24-2019, 01:01 AM   #1 (permalink)
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Gearing and tire size

So I'm about to commit the cardinal sin of ecomodder and get a lift on my Jeep and bigger tires. I'm wondering how I can calculate the final gearing so I can compare my new setup to stock.

The stock specs of my Jeep are:
3.54:1 axle gears
225/75R15 tires (I think approximately 28" diameter)

How can I compare that setup to a different one?

This is something an example I have in mind:

4.56:1 gearing
33x10.5 tires

Please post how you come to your answer so I can do it myself for different scenarios. I want to pick the best gear and tire combo for what I'll be using my jeep for.

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Old 03-24-2019, 10:34 AM   #2 (permalink)
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This site offers the formula for how to use tire size to calculate tire diameter:
https://auto.howstuffworks.com/auto-...size-chart.htm

tire diameter:

(CROSS SECTION WIDTH x 0.ASPECT RATIO x 2 ÷ 25.4) + WHEEL DIAMETER = OVERALL TIRE DIAMETER

For Example:

235/45ZR-17

(235 x 0.45 x 2 ÷ 25.4) + 17 = 25.327"

And here's a calculator for the rest of your query:
https://tiresize.com/gear-ratio-calculator/
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Old 03-24-2019, 12:48 PM   #3 (permalink)
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Take the tire size calculator difference and multiply all your distance related math with it. A ScanGague or UltraGague comes in handy because you can simply calibrate your odometer readings through it.
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Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

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Old 03-24-2019, 03:03 PM   #4 (permalink)
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Quote:
Originally Posted by Fat Charlie View Post
Take the tire size calculator difference and multiply all your distance related math with it. A ScanGague or UltraGague comes in handy because you can simply calibrate your odometer readings through it.
You know, I realized that I think I've been calculating my distance traveled wrong. I've been assuming that my stock tire size was 29 inches instead of about 28... So I should be multiplying my distance by 1.07 instead of 1.04
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Old 03-24-2019, 03:15 PM   #5 (permalink)
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There is a sticker in your door jam that that states what size tire came stock on your vehicle. Look on both sides if you don’t find it near the driver’s door.
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Old 03-26-2019, 12:35 PM   #6 (permalink)
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Thanks! All the replies are very helpful. It helped me realize I've been calculating my odometer wrong.
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Old 03-26-2019, 01:56 PM   #7 (permalink)
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Yeah, there's a lot of zigging and zagging and double negatives. But it does what you want it to do.

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Quote:
Originally Posted by sheepdog44 View Post
Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

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