Seeking Gear Ratio Suggestions
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Laughing Gas
Joined: Nov 2016
Posts: 856
Likes: 63
From: Oxnard
Seeking Gear Ratio Suggestions
1979 Ford F100 with OEM 9” and 273 gearing. 5.0L Gen 3 Coyote Swap with 10R80 transmission about ~ two weeks from being done. Existing tires 205/75R15 being replaced with 235/75R15. Shop owner informed me that I should be open to changing gear ratio to something like 323 or 350. Seeking suggestions with others experiences doing the Coyote and 10R80 swap. Truck will be used for some around town driving and ~ 700 mile trips fishing a couple times a years. Thanks,
Fleet Mechanic
Joined: Feb 2022
Posts: 1,377
Likes: 709
I generally like to be turning a little less than 2000RPM at 70 in the numerically lowest gear ratio. A 3.73 would put you at 2100-ish in 9th (0.69) and 1900-ish in 10th (0.64). Your problem is the steep 1st gear ratio (4.7). With the size and width tire you're running it is going to be a smoke show every time you launch. Although the Coyote is a bit of a peaky, high revving engine it should easily have enough torque to achieve good gradeability in 9th or 10th though without experiencing shift busyness (depending of course on how the pattern was calibrated) so maybe a 3.5 is a good compromise?
This is all about compromises. You're going to have to make one somewhere. Do you want to keep the engine speeds lower on the highway and accept a lot of downshifts to maintain a grade or accelerate, or do you want to avoid that but then deal with the fact that you are going to be buying a lot of tires if you are a heavy footed driver? It might help if you go with a wheel that is a bit wider. 235s being subjected to that kind of power with no weight over the rear axle is a little silly.
This is all about compromises. You're going to have to make one somewhere. Do you want to keep the engine speeds lower on the highway and accept a lot of downshifts to maintain a grade or accelerate, or do you want to avoid that but then deal with the fact that you are going to be buying a lot of tires if you are a heavy footed driver? It might help if you go with a wheel that is a bit wider. 235s being subjected to that kind of power with no weight over the rear axle is a little silly.
Last edited by Viper Pilot; Jun 8, 2026 at 11:54 AM.
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Laughing Gas
Joined: Nov 2016
Posts: 856
Likes: 63
From: Oxnard
Ha Viper Pilot,
Like your thinking and I'm with you, with the sweet spot RPM between ~ 1950 and 2150 at 70 MPH. Definitely no heavy foot here, Commercial Driver License background where as we anticipate lights avoiding coming to full stop, saves on fuel and allot of shifting. The 235/75R15 tires are practically new that I'll use until they surpass the DOT date and then change. Want to stay with my Ford OEM 10 hole aluminum wheels, considering my OEM wheel width limitation what tire size is suggested with 3.50 gearing?
Like your thinking and I'm with you, with the sweet spot RPM between ~ 1950 and 2150 at 70 MPH. Definitely no heavy foot here, Commercial Driver License background where as we anticipate lights avoiding coming to full stop, saves on fuel and allot of shifting. The 235/75R15 tires are practically new that I'll use until they surpass the DOT date and then change. Want to stay with my Ford OEM 10 hole aluminum wheels, considering my OEM wheel width limitation what tire size is suggested with 3.50 gearing?
Hotshot
Joined: Jul 2020
Posts: 10,519
Likes: 2,654
From: Near Salt Lake City
I would leave the gear ratio where it is until you drive it around some
You are liable not to notice the low gears with the engine and trans upgrade
I would not go higher than 3.50 or so ratio even if you do decide to change the ratio
You are liable not to notice the low gears with the engine and trans upgrade
I would not go higher than 3.50 or so ratio even if you do decide to change the ratio
Fleet Mechanic
Joined: Feb 2022
Posts: 1,377
Likes: 709
Ha Viper Pilot,
Like your thinking and I'm with you, with the sweet spot RPM between ~ 1950 and 2150 at 70 MPH. Definitely no heavy foot here, Commercial Driver License background where as we anticipate lights avoiding coming to full stop, saves on fuel and allot of shifting. The 235/75R15 tires are practically new that I'll use until they surpass the DOT date and then change. Want to stay with my Ford OEM 10 hole aluminum wheels, considering my OEM wheel width limitation what tire size is suggested with 3.50 gearing?
Like your thinking and I'm with you, with the sweet spot RPM between ~ 1950 and 2150 at 70 MPH. Definitely no heavy foot here, Commercial Driver License background where as we anticipate lights avoiding coming to full stop, saves on fuel and allot of shifting. The 235/75R15 tires are practically new that I'll use until they surpass the DOT date and then change. Want to stay with my Ford OEM 10 hole aluminum wheels, considering my OEM wheel width limitation what tire size is suggested with 3.50 gearing?
You can play around with all of this stuff here:
https://purperformance.com/p-29669-rpm-calculator.html
Last edited by Viper Pilot; Yesterday at 07:29 AM.
Laughing Gas
Joined: May 2021
Posts: 1,174
Likes: 362
From: Anderson, California
ok, using the above calculator,
I get 1,991 rpms running 70-mph with 4:10 gearing in .64 OD (10th ?) and 31-inch rubber. _ eh ?
and
at 100-mph above at 1:1 direct, you'd be turning 4,444-rpms easy peasy for a Coyote.
I get 1,991 rpms running 70-mph with 4:10 gearing in .64 OD (10th ?) and 31-inch rubber. _ eh ?
and
at 100-mph above at 1:1 direct, you'd be turning 4,444-rpms easy peasy for a Coyote.
Last edited by Greaser007; Yesterday at 07:55 PM.
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