The axle ratio is the number of turns from the final drive it takes for one turn of the wheel.

This is further multiplied or reduced by the transmission gear-sets.
So really what is important is the overall ratio, even the wheel size affects this..

Thanks, it is revs of the drive shaft to the axel.

Sorry about by typo: Ration of course I meant Ratio.

I did check and the 2.8L 3.42 Ratio Colorado (Chevy) does about 2000 RPM at 60 MPH. So, it is really high geared, good for gas mileage, but not so good when pulling a load. I guess this truck will see a lot of 4th gear use. They in effect consider the 5th gear to be "overdrive" anyway. The turck is lised as 5 Speed/Overdrive manual.

Many of today's car have "overdrive" ratios, or simply more gears(fifth and sixth may be "overdrive").
A true overdrive is an added gear-set that reduces the final drive by 0.70- the standard 3 speed at that time was then effectively a 5 speed..
The Rambler I had was equipped with an optional overdrive, but it never worked for me as the solenoid was inoperative and I was about broke..

The 3.7x ratio in the Colorado is a 3.73. That's an axle GM has used for a long time, along with the 3.42.

So, in the case of a 3.73 axle, the driveshaft rotates 3.73 times for every turn of the axle. That will be the same as the number of times the engine turns per revolution of the axle if you are in a gear that has a 1.0 ratio, which is usually 4th in a truck with a 5-speed manual overdrive. If you're in 5th and it's a .70 ratio, the engine would turn 3.73 x .70 (2.61 times) for each revolution of the axle.

You can figure out the RPM at 60 MPH if you know the diameter of the tire, the axle ratio, and the ratio in overdrive in the transmission. For example, on my S10, which has a 3.73 axle and a .70 overdrive ratio in 5th gear, here's how it works:

Wheel diameter (including tires of course): 29.5" Multiply that by pi (3.14) to get the circumference of the wheel, which is 92.63"

There are 63,360 inches in a mile, so you take that divided by 92.63 to get (rounded) 684. That means that the wheels turn 684 times for every mile the truck travels.

Take 684 x 3.73 (axle ratio) and you find that the driveshaft turns 2551 times per mile.

Multiply 2551 x .70 (transmission ratio in overdrive) and you find that the engine turns 1,786 times per mile when the truck is in overdrive. The number of engine revolutions per mile is the same as the engine RPM at 60 MPH, so this truck turns about 1,800 RPM at 60 MPH in overdrive, and that's just about what the tach shows. (It has somewhat larger than normal tires, so most vehicles with a 3.73 would turn a little higher RPMs than this.) If you want to know the engine revolutions at 60 MPH in some other gear, such as 4th gear, you just multiply by that gear's ratio rather than the overdrive ratio. So, if 4th is a 1.0 ratio, the RPM at 60 MPH on this truck in 4th would be 2,551.

Changing the axle ratio from 3.73 to 3.42 would lower the RPM at 60 MPH in overdrive from 1,786 to 1,638, so it's not a huge difference. Still, I'd probably get the 3.73 on the Colorado if you plan to do much towing, since it'd be easier to take off from a dead stop with the 5-speed (less clutch slipping and longer clutch life) if you had the shorter (higher numerical) axle ratio.

Cowboyind,

Thanks for the details, you read more like an engineer than a cowboy. I'm an electrical engineer, so your explaination is easy to follow, and understood. What year is your S10? How has it been: reliability, gas mileage, fit and finish? Too late for me to change to a Ranger (the other truck I was looking at), but I will appreciate any owner insights.

I have to look to see which axel ratio I have, but I can say the indicated rpm in 5th gear is below 2000. I have the base version, and the smaller tires: 205R75-15, giving me a lower "grearing" too. I believe the upgrade tire is 225R75-15, which is wider and taller, as you know, but not by much, suppose the difference does add up when the wheels are really "turning".

I'm still on my fist tank of gas and driving in a rural area, few traffic lights. The gas gauge is now reading about 1/8th down (but I expect it to drop to 3/4 real fast) and I have about 115 miles on this tank. Looks like I'll get great mileage. The tank capacity is 19.5 Gallon. We'll see after I get an average of several fill ups.

As I may have said in this email, I was driving a 1988 Dodge Ram 50, 2.6L 4WD, extended cab, lots of "good stuff". It had gotten to the point that looked as if everything was about ready to go. So I decided with all the sales and cash back now was the time to get a new truck. I didn't look at Dodge, was somewhat intersted in the Toyota, but not the price.

Thanks, Jerry, and congratulations on your new truck.

My S10 is the ZR2 4x4 model, and I love it. It's a 2003, has 32,600 miles on it, and I have not had a single problem with it since I bought it in October of 2002. The dealer had to look hard to find me a ZR2 5-speed, because they're rare, but I really like manual transmissions and they did find one and got it from the other dealer.

The fact that mine is the 4x4 and ZR2 model which sits up higher than standard models hurts the gas mileage. Even with the 5-speed, I struggle to get 20 mpg on the highway. I know other people with V6 regular S10s that get better mileage, like low to mid 20s on the highway. If you got the Colorado I bet you'll do better than that.

The fit and finish on my truck is great. Considering how hard it rides due to the off-road suspension package, I'm amazed that there aren't a bunch of squeaks and rattles, but there aren't any.