Gearing calculator
Thread Starter
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Tuned
Joined: Dec 2011
Posts: 313
Likes: 8
From: Wyotana
Gearing calculator
I'm looking for a gearing calculator that I can plug and play axle gearing as well as tire size.
What I am trying to do:
I have a 2000 F-350 dually 7.3 PSD, 6 speed ZF trans and 3.73 gears. When I tow over 10K the truck falls on it's face in OD (6th gear). I want to gear it to do 2000-2100 RPM in 5th gear (direct gear) at 65-70 mph. My old IDI could do this with 3.55 gears. What way can I do this with tire size rather than 2 new gear sets? I have an abundance of semi 22.5" rims and was looking into the super lo-pro size of 255/70/22.5. This changes my tire OD from 31.7" to 37".
OK, but does that put me where I want to be???
Will I have to lift my truck for 37" tires?? If so, how much?
What I am trying to do:
I have a 2000 F-350 dually 7.3 PSD, 6 speed ZF trans and 3.73 gears. When I tow over 10K the truck falls on it's face in OD (6th gear). I want to gear it to do 2000-2100 RPM in 5th gear (direct gear) at 65-70 mph. My old IDI could do this with 3.55 gears. What way can I do this with tire size rather than 2 new gear sets? I have an abundance of semi 22.5" rims and was looking into the super lo-pro size of 255/70/22.5. This changes my tire OD from 31.7" to 37".
OK, but does that put me where I want to be???
Will I have to lift my truck for 37" tires?? If so, how much?
Laughing Gas
Joined: Mar 2002
Posts: 948
Likes: 342
From: Newton Illinois
I set this up a excel spreadsheet so I could play around with gear ratios and tire size when I was building a truck
you take your real axel ratio x the trans ratio (in each gear if you want) to get a total gear ratio, the divide the engine RPM by that total ratio and that will give you a rear axel RPM
Then take the rear axel RPM X the tire circumference and that will give you inches per minute, then divide that by 63,360 (inches in a mile) that will give you miles per minute, then multiply that X 60 for miles per hour.
you take your real axel ratio x the trans ratio (in each gear if you want) to get a total gear ratio, the divide the engine RPM by that total ratio and that will give you a rear axel RPM
Then take the rear axel RPM X the tire circumference and that will give you inches per minute, then divide that by 63,360 (inches in a mile) that will give you miles per minute, then multiply that X 60 for miles per hour.
Fleet Mechanic
Joined: Mar 2013
Posts: 1,661
Likes: 1,062
From: Montana
Here are a few different online calculators that'll do the number crunching for you.
https://tiresize.com/gear-ratio-calculator/
https://www.intercotire.com/tire_siz...tio_calculator
https://spicerparts.com/calculators/...rpm-calculator
https://tiresize.com/gear-ratio-calculator/
https://www.intercotire.com/tire_siz...tio_calculator
https://spicerparts.com/calculators/...rpm-calculator
Lead Driver
Joined: Jun 2006
Posts: 5,663
Likes: 985
From: Near Yosemite CA
No, it does not, taller tires reduce your gearing... if you go from a ~32" tire to a 37" tire it would be the adverse of what you are wanting... and as a side note, OD is not meant for towing.
Thread Starter
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Tuned
Joined: Dec 2011
Posts: 313
Likes: 8
From: Wyotana
Yes, I want to tow in direct, but want to do more than 55 mph
Thread Starter
|
Tuned
Joined: Dec 2011
Posts: 313
Likes: 8
From: Wyotana
I set this up a excel spreadsheet so I could play around with gear ratios and tire size when I was building a truck
you take your real axel ratio x the trans ratio (in each gear if you want) to get a total gear ratio, the divide the engine RPM by that total ratio and that will give you a rear axel RPM
Then take the rear axel RPM X the tire circumference and that will give you inches per minute, then divide that by 63,360 (inches in a mile) that will give you miles per minute, then multiply that X 60 for miles per hour.
you take your real axel ratio x the trans ratio (in each gear if you want) to get a total gear ratio, the divide the engine RPM by that total ratio and that will give you a rear axel RPM
Then take the rear axel RPM X the tire circumference and that will give you inches per minute, then divide that by 63,360 (inches in a mile) that will give you miles per minute, then multiply that X 60 for miles per hour.
Thread Starter
|
Tuned
Joined: Dec 2011
Posts: 313
Likes: 8
From: Wyotana
According to the Spicer calculator, I'd need 3.08 gears to get to 2200 at 68mph in direct gear with the stock tires.
Running the 37" 22.5 tires and slowing to 65mph will get me right where I want to be to tow in direct (5th) gear. I'm guessing I'll use 1st gear (granny low) a lot more. I may have to use the transfer case to get my heaviest (20K) loads going.
Running the 37" 22.5 tires and slowing to 65mph will get me right where I want to be to tow in direct (5th) gear. I'm guessing I'll use 1st gear (granny low) a lot more. I may have to use the transfer case to get my heaviest (20K) loads going.
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