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Taylor95 03-24-2019 02:01 AM

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.

California98Civic 03-24-2019 11:34 AM

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/

Fat Charlie 03-24-2019 01:48 PM

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.

Taylor95 03-24-2019 04:03 PM

Quote:

Originally Posted by Fat Charlie (Post 594526)
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

me and my metro 03-24-2019 04:15 PM

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.

Taylor95 03-26-2019 01:35 PM

Thanks! All the replies are very helpful. It helped me realize I've been calculating my odometer wrong.

Fat Charlie 03-26-2019 02:56 PM

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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