Gear Ratio
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Tuned
Joined: Jan 2018
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Gear Ratio
Anyone tell me what the "standard" tire size is figured for 3.73 gear. If it is 245/75/17 and my truck has the 275/70/18, my effective gear is 3.54. If the standard size is 275/65/18, that makes the 275/70/18 effective ratio 3.61. If the 3.73 is figured on the 275/70/18, that makes the 245/75/17 a 3.93 ratio. Just curious what actual ratio my truck has and this is the place to get an answer.
Elder User
Joined: Jan 2004
Posts: 566
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From: Florence SC
I don’t understand the question. If you have 3.73 gears, the pinion turns 3.73 revolutions for every one revolution of the carrier. You can figure “effective ratio” to compare tire sizes, but there is no tire size that factors into the 3.73 calculation. That’s just # of teeth on ring divided by # teeth on pinion.
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Tuned
Joined: Jan 2018
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I don’t understand the question. If you have 3.73 gears, the pinion turns 3.73 revolutions for every one revolution of the carrier. You can figure “effective ratio” to compare tire sizes, but there is no tire size that factors into the 3.73 calculation. That’s just # of teeth on ring divided by # teeth on pinion.
Hotshot
Joined: Jun 2003
Posts: 12,340
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From: SW VA
You a overthinking this. There is no "standard tire size" to give you a 3.73 ratio. I guess if you want to do it your way...find the tire size that comes standard on a base model XL with no options. Anything else will be "non-standard"
Fleet Mechanic
Joined: May 2017
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From: Oregon
This would be the way to do it. Start with the smallest "stock" tire offered which is the 245 on an XL.
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Tuned
Joined: Oct 2003
Posts: 463
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From: COLORADO, USA
I'm also curious about this. I swapped out my stock STX wheels/tires with a set from a Lariat with the 20's. Side by side, the new wheels/tires are a good 2" taller overall. I'm curious what my gear ratio now is. I would imagine it's near a 4.10
Logistics Pro
Joined: Apr 2017
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From: Lost in the Ozone....
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Tuned
Joined: Jan 2018
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I have done that, if the 245/75/17 is considered standard equipment and I option the 275/70/18, my effective ratio becomes 3.54. A 4.30 becomes 4.08. The XLT and STX packages default to 275/65/18. So my Question, which one? They all have the same axle.
Fleet Mechanic
Joined: May 2017
Posts: 1,753
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From: Oregon
I guess I don't know what you're asking then. The smallest stock tire and wheel is the 245/75-17. Put in whatever size you want to upsize to in one of the calculators and that's your "final" ratio. This is exactly why I ordered mine to get the 4.30's because with the "stock" 275/70-18's, which I also ordered, put me at 4.09's. When it's time for new tires I'll probably go to 295's which will get me to 3.90 ish.... although I'm not sure I really want to go down anymore in gearing as I really like the way it pulls as it is.
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