4.88 vs 5.14 gear
11-08-2007, 11:29 PM
#1
Senior Member
Thread Starter
4.88 vs 5.14 gear
everyone is telling me that 4.88 is what i want when i run 37" tires. in a perfect world, a 37" tire with a 4.60 gear (yes i know they dont make that) would give me the same final drive ratio as stock. i want something slightly lower then stock to help with bottom end torque. the truck as it is in torquey enough for me and with the 37s itll be worse.
after doing some research i found a set of 5.14 gears. if 4.60 would give me a stock final drive ratio im thinking that 5.14 is the gear for me. its only .54 revolutions of the drive shaft (to make the wheel spin once) more then stock.
for those having trouble following my math, basically it would be the exact same as if i went from 3.73 to 4.30 and kept my stock sized tires. going from 3.73 to 4.30 means the drive shaft spins .57 more rpms more then stock to make the wheel turn once.
i know with my mustang, i went from 2.73 to 3.73 and bottom end power was great and it didnt really add that many rpms on the motor when driving. so my thought is this, 2.73 to 3.73 is a full extra rotation of the drive shaft to spin the wheels once. i want to go with 5.14 gears and a 37" tire and that will only make the drive shaft spin .54 more times then stock. therefor, with 37" tires and 5.14 gears engine rpms wont go up that much and ill still gain some bottom end power (which will be needed for the extra weight of all that rubber)
i almost never drive on the freeway so for those thinking that 5.14 is way too low for the freeway, first.....its not, and second, i rarely use the freeway. i havent done the math on paper but crusing rpms will only be a couple hundred rpms over stock for any given speed when running the 5.14 gear with 37" tire. plus this leaves me room later on to run a bigger tire. i havent ruled out the possibility of putting in a leveling kit and a bigger block (on top of the 6" suspension lift and 3" body lift).
what do you guys think?
after doing some research i found a set of 5.14 gears. if 4.60 would give me a stock final drive ratio im thinking that 5.14 is the gear for me. its only .54 revolutions of the drive shaft (to make the wheel spin once) more then stock.
for those having trouble following my math, basically it would be the exact same as if i went from 3.73 to 4.30 and kept my stock sized tires. going from 3.73 to 4.30 means the drive shaft spins .57 more rpms more then stock to make the wheel turn once.
i know with my mustang, i went from 2.73 to 3.73 and bottom end power was great and it didnt really add that many rpms on the motor when driving. so my thought is this, 2.73 to 3.73 is a full extra rotation of the drive shaft to spin the wheels once. i want to go with 5.14 gears and a 37" tire and that will only make the drive shaft spin .54 more times then stock. therefor, with 37" tires and 5.14 gears engine rpms wont go up that much and ill still gain some bottom end power (which will be needed for the extra weight of all that rubber)
i almost never drive on the freeway so for those thinking that 5.14 is way too low for the freeway, first.....its not, and second, i rarely use the freeway. i havent done the math on paper but crusing rpms will only be a couple hundred rpms over stock for any given speed when running the 5.14 gear with 37" tire. plus this leaves me room later on to run a bigger tire. i havent ruled out the possibility of putting in a leveling kit and a bigger block (on top of the 6" suspension lift and 3" body lift).
what do you guys think?
11-09-2007, 02:15 PM
#3
Senior Member
You've got the right idea in your comparison, but I suggest to use ratios (division) instead of differences (subtraction) to give a better idea of the expected changes.
For example, taking your 4.60 ratio with 37" being equivalent to stock.
The formula I use in various formats is: old tire height / old gear ratio = new tire height / new gear ratio.
If the tire size is kept constant, then your RPMs should be 4.88/4.60=1.06, and 5.14/4.60=1.12 times as fast - meaning that your RPMs will be 6% and 12% higher than the stock equivalent ratio for a given speed. This should roughly equate to a similar improvement in 'off-the-line' oomph.
Taking this one step further, if the 5.14 ratio is chosen, then the tire height for equal RPMs as the 37"s with a 4.60 is 37/4.60 x 5.14 = 41.3" - pretty big honkin' tire!
One final note - be sure the high ratio can withstand the stresses for your application. I've heard of a problem with smaller axle housings in that to make things fit, the pinion gear gets pretty small physically and may shear under extreme loads.
For example, taking your 4.60 ratio with 37" being equivalent to stock.
The formula I use in various formats is: old tire height / old gear ratio = new tire height / new gear ratio.
If the tire size is kept constant, then your RPMs should be 4.88/4.60=1.06, and 5.14/4.60=1.12 times as fast - meaning that your RPMs will be 6% and 12% higher than the stock equivalent ratio for a given speed. This should roughly equate to a similar improvement in 'off-the-line' oomph.
Taking this one step further, if the 5.14 ratio is chosen, then the tire height for equal RPMs as the 37"s with a 4.60 is 37/4.60 x 5.14 = 41.3" - pretty big honkin' tire!
One final note - be sure the high ratio can withstand the stresses for your application. I've heard of a problem with smaller axle housings in that to make things fit, the pinion gear gets pretty small physically and may shear under extreme loads.
11-09-2007, 03:40 PM
#4
Senior Member
Thread Starter
You've got the right idea in your comparison, but I suggest to use ratios (division) instead of differences (subtraction) to give a better idea of the expected changes.
For example, taking your 4.60 ratio with 37" being equivalent to stock.
The formula I use in various formats is: old tire height / old gear ratio = new tire height / new gear ratio.
If the tire size is kept constant, then your RPMs should be 4.88/4.60=1.06, and 5.14/4.60=1.12 times as fast - meaning that your RPMs will be 6% and 12% higher than the stock equivalent ratio for a given speed. This should roughly equate to a similar improvement in 'off-the-line' oomph.
Taking this one step further, if the 5.14 ratio is chosen, then the tire height for equal RPMs as the 37"s with a 4.60 is 37/4.60 x 5.14 = 41.3" - pretty big honkin' tire!
One final note - be sure the high ratio can withstand the stresses for your application. I've heard of a problem with smaller axle housings in that to make things fit, the pinion gear gets pretty small physically and may shear under extreme loads.
For example, taking your 4.60 ratio with 37" being equivalent to stock.
The formula I use in various formats is: old tire height / old gear ratio = new tire height / new gear ratio.
If the tire size is kept constant, then your RPMs should be 4.88/4.60=1.06, and 5.14/4.60=1.12 times as fast - meaning that your RPMs will be 6% and 12% higher than the stock equivalent ratio for a given speed. This should roughly equate to a similar improvement in 'off-the-line' oomph.
Taking this one step further, if the 5.14 ratio is chosen, then the tire height for equal RPMs as the 37"s with a 4.60 is 37/4.60 x 5.14 = 41.3" - pretty big honkin' tire!
One final note - be sure the high ratio can withstand the stresses for your application. I've heard of a problem with smaller axle housings in that to make things fit, the pinion gear gets pretty small physically and may shear under extreme loads.
thats some very good info. ive hear something similar about the low gears being small and more easily broken. ill ask the 4wheelparts when i go shopping for parts. i dont think ill have much to worry about because ill probably only make about 270rwhp and will only be doing light offroading (open fields, puddles, sand dunes, etc.) its primarily a daily driver.
with that said, i looked up on the internet for a rpm calculator and entered all the info (tire size, tranny ratio, gears) and the difference between 4.88 and 5.14 (at 85mph) is only 150rpm difference (150rpm more with the 5.14) since 85 is the fastest i need to go on the freeway and rpms will still be under 3000 at that speed, im going with 5.14s more bottom end oomph with only slightly more rpms for any given speed.
what is the axle spline count? i have a brand new locker in my room i never put in my mustang but its for 31 spline axles.
