Question on gear ratios
#1
02-27-2005, 02:57 PM
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Question on gear ratios
From what I understand a numerically lower gear ratio gives you better acceleration but less low end torque. Higher numbers are for trucks that will be used more for pullung. Is that corret or what is the differences?
#2
02-27-2005, 04:56 PM
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RE: Question on gear ratios
Not quite. A numerically high number will give you faster accelleration and better towing capacity. Numerically lower gear ratios will give you lower cruise RPMs, better fuel economy, higher top speed, and less wear on the drivetrain. Of course all of that is modified by the catch-all "to a point".
There's a point where if your ratio is too tall (numerically low) you'll be lugging it all the time, having to flog it to get moving, and you'll get worse mileage and it'll be a lot harder on the engine and tranny. Same goes for the other direction - if you go too short on the ratio (numerically high) you won't have good accelleration because you'll have to shift all the time and it'll just wrap out the motor constantly.
About 3:1 or so is a good target for a freeway cruising truck that doesn't haul much of a load and if the owner isn't too heavy on the gas. 3.5 - 3.75:1 is a good all-around target for a truck that sees occasional hauling duties and still gets a fair bit of street driving. 4:1 is more for trucks that'll haul stuff often or one that has big tires, or if the owner has a lead foot and wants accelleration. 4.5:1 and up are pretty much for off-road trucks with huge tires.
There's a point where if your ratio is too tall (numerically low) you'll be lugging it all the time, having to flog it to get moving, and you'll get worse mileage and it'll be a lot harder on the engine and tranny. Same goes for the other direction - if you go too short on the ratio (numerically high) you won't have good accelleration because you'll have to shift all the time and it'll just wrap out the motor constantly.
About 3:1 or so is a good target for a freeway cruising truck that doesn't haul much of a load and if the owner isn't too heavy on the gas. 3.5 - 3.75:1 is a good all-around target for a truck that sees occasional hauling duties and still gets a fair bit of street driving. 4:1 is more for trucks that'll haul stuff often or one that has big tires, or if the owner has a lead foot and wants accelleration. 4.5:1 and up are pretty much for off-road trucks with huge tires.
#3
02-28-2005, 11:09 AM
RE: Question on gear ratios
ORIGINAL: horatio102
Not quite. A numerically high number will give you faster accelleration and better towing capacity. Numerically lower gear ratios will give you lower cruise RPMs, better fuel economy, higher top speed, and less wear on the drivetrain. Of course all of that is modified by the catch-all "to a point".
There's a point where if your ratio is too tall (numerically low) you'll be lugging it all the time, having to flog it to get moving, and you'll get worse mileage and it'll be a lot harder on the engine and tranny. Same goes for the other direction - if you go too short on the ratio (numerically high) you won't have good accelleration because you'll have to shift all the time and it'll just wrap out the motor constantly.
About 3:1 or so is a good target for a freeway cruising truck that doesn't haul much of a load and if the owner isn't too heavy on the gas. 3.5 - 3.75:1 is a good all-around target for a truck that sees occasional hauling duties and still gets a fair bit of street driving. 4:1 is more for trucks that'll haul stuff often or one that has big tires, or if the owner has a lead foot and wants accelleration. 4.5:1 and up are pretty much for off-road trucks with huge tires.
Not quite. A numerically high number will give you faster accelleration and better towing capacity. Numerically lower gear ratios will give you lower cruise RPMs, better fuel economy, higher top speed, and less wear on the drivetrain. Of course all of that is modified by the catch-all "to a point".
There's a point where if your ratio is too tall (numerically low) you'll be lugging it all the time, having to flog it to get moving, and you'll get worse mileage and it'll be a lot harder on the engine and tranny. Same goes for the other direction - if you go too short on the ratio (numerically high) you won't have good accelleration because you'll have to shift all the time and it'll just wrap out the motor constantly.
About 3:1 or so is a good target for a freeway cruising truck that doesn't haul much of a load and if the owner isn't too heavy on the gas. 3.5 - 3.75:1 is a good all-around target for a truck that sees occasional hauling duties and still gets a fair bit of street driving. 4:1 is more for trucks that'll haul stuff often or one that has big tires, or if the owner has a lead foot and wants accelleration. 4.5:1 and up are pretty much for off-road trucks with huge tires.
When sizing gears, you want to take all things into consideration. If you're looking for mileage, you want to be at the RPM your motor makes it's peak torque when you're at your primary cruising speed on the highway (70-75mph for me).
I've posted pictures of my Blazer on here before. When it was stock, it had 31" tires and 3.08:1 gears. It couldn't get out of it's own way, was always downshifting, and got about 11mpg on the freeway. I went to 10" of lift, big *** winch bumper, and had 33" street tires and 4.10:1 gears. At 70mph I was at 2000 RPM, which was where I made peak torque, and I got 19-21mpg on average.
#4
02-28-2005, 11:38 AM
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RE: Question on gear ratios
Just took out the 4.10's for 4.56's....WOW!! Moves that 5500#'s pretty good now![sm=gears.gif]
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Quick
#5
02-28-2005, 12:45 PM
Champion
RE: Question on gear ratios
Well dad's yukon has rediculously tall gears in it - I thought they were around 3:1 - and it seems to do just fine. It's not a performer by any means, cruising at 70 it's at about 1800 iirc and gets 17mpg.
#6
02-28-2005, 12:59 PM
RE: Question on gear ratios
With stock tires I bet it has 3.73's in it, which is a good combination. POSSIBLY 3.42's, which is what I had in my '90 Chevy stepside, and it did pretty reasonable on gas, but it had a 305 in it too which helped also. It's probably the weight that kills the acceleration on the Yukon.
#7
02-28-2005, 01:01 PM
RE: Question on gear ratios
jhalfhill, WHERE did you come up with a lower numerical gear gets better accel? The opposite is true as mentioned above. One reply above discusses tire diameter in conjunction with gear ratios. That is important! Too few younger types understand tire diameter changing does the same thing as rearend gear ratio changing and can be done a lot cheaper, too and tires need replacement anyhow. Typically, when I order any type of vehicle, I get the highest numerical gear ratio available. Today's transmissions with overdrive ratios cut the rpm's on the highway plenty far and by getting the lower gear (higher numerical number) it allows me to still be geared right when I put on the bigger tires I always do.