88Mj4.0 Posted June 16, 2023 Share Posted June 16, 2023 Hello! I’m new to the forum and new to working on cars in general and I have a couple of questions about the gear ratio. I’ve read a couple forums saying that you should switch the ratio if you get a lift and bigger tires. I just bought a 4.5” lift for my 88 Comanche 4.0 and the wheels are 15in and the tires have an aspect ratio of 75. I want to put 32.5s on the the 15in wheel cuz I think the wheel looks cool the way it is and new wheels are just expensive. My question is what should my gear ratio be? I’m trying to turn this into my daily car and I drive a lot. I’m also getting the suspension and bigger tires for off-road purposes so I want it to cater to both an everyday use and off road. Also how can I improve my mpg? Link to comment Share on other sites More sharing options...
Pete M Posted June 16, 2023 Share Posted June 16, 2023 a lift and big tires will lower your MPGs, regardless of ratio. what transmission do you have? Link to comment Share on other sites More sharing options...
Drahcir495 Posted June 16, 2023 Share Posted June 16, 2023 This may help you -> https://tiresize.com/gear-ratio-calculator/ Link to comment Share on other sites More sharing options...
88Mj4.0 Posted June 17, 2023 Author Share Posted June 17, 2023 14 hours ago, Pete M said: a lift and big tires will lower your MPGs, regardless of ratio. what transmission do you have? I don’t know what transmission I have it’s whatever came with it. Should I upgrade? And I know that it’ll lower my mpg I’m just trying to imprint as much as I can with the lift and tires. Link to comment Share on other sites More sharing options...
Pete M Posted June 17, 2023 Share Posted June 17, 2023 manual or automatic? Link to comment Share on other sites More sharing options...
88Mj4.0 Posted June 17, 2023 Author Share Posted June 17, 2023 Manual Link to comment Share on other sites More sharing options...
Pete M Posted June 17, 2023 Share Posted June 17, 2023 I would do 4.56. Link to comment Share on other sites More sharing options...
derf Posted June 17, 2023 Share Posted June 17, 2023 Full tire size is important. A 225/75R15 is a lot smaller than a 315/75R15. The first number is the section width and the aspect ratio is a percentage of the section width to figure out sidewall height. Your stock gear ratio is probably 3.08, which is mostly for fuel economy. You want to go with a higher number gear set. Your options are 3.55, 3.73, 4.10, and 4.56. You can go more but if you're under 35" for tire size more gear is too much. Go to http://www.grimmjeeper.com/gears.html to figure out how things perform. Select the Peugeot BA-10 in the transmission drop down list. You can ignore the transfer case and underdrive. Put in the gear ratio and stock tire size. There is a button to copy everything to the other column. Put in the new tire size. Then try the other gear ratios with the new tire sizes. In the charts below you can see how fast the engine revs on the road. You want the numbers in the last chart with the new tire size to be a little higher than with the old tires. How much higher is up to you. Link to comment Share on other sites More sharing options...
88Mj4.0 Posted June 18, 2023 Author Share Posted June 18, 2023 23 hours ago, Pete M said: I would do 4.56. What about for an automatic lol? That’s my bad I made a mistake wasn’t thinking straight. My stock ratio is a 3.54. Link to comment Share on other sites More sharing options...
Pete M Posted June 18, 2023 Share Posted June 18, 2023 still 4.56. Link to comment Share on other sites More sharing options...
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