What does the gear ratio translate to 4:11, 5:14 etc......? Is one for fast start or top end or what. It's confusing.......
What it means is the ratio is actually 4.11 to 1. The driveshaft will turn 4.11 times for every time the axle shaft turns the wheel. The higher the number (numerically) the deeper the gears are, which means they are more suited to launching the car as opposed to top end. A 2.75 to 1 rear would be considered "high" and more for freeway driving to lower the rpms of the motor. A 4.11 to 1 is considered "lower" and is more suited to performance off the line usage. Confusing, isn't it ??? Don
It is 4.11:1 and 5.14:1, expressed as ratios. So, for a 4.11:1 ratio, it takes 4.11 turns of the driveshaft to make one turn at the axles. The higher the number to the left of the colon is, the "lower" the gear ratio is. The lower the gear ratio is, the quicker the launch, but the lower the top speed. The higher (numerically lower) the gear ratio, the slower the launch, but the higher the top speed. Given enough power, a car with a 2.50:1 rear gear might go 200mph at redline, but take a while to get there. The same car, with a 5:14 might turn a 10.00 second 1/4 mile, but top out at 125.
To make it a little easier to understand, let's use round numbers. If you had a car with 4.0 to 1 gears and the motor was turning 2,000 rpms, the axle would be turning at 500 rpms. If you had 2.0 to 1 gears in the rear at the same 2000 rpms the axles would be going around at 1,000 rpms. It would seem that the higher gear ratio (numerically lower) 2.0 would be faster, and they might at top end, but you have to get the mass of the car moving from a dead stop and the engine would be lugging to get that done with the 2.0 ratio. The 4.0 will get the car moving much quicker. Don
Remember as well, tire height plays a role in this equation too. While it does not change gear ratio, the circumference of the rear tires determines how far you go in one turn of the tires. Putting taller tires on the same vehicle can make it "seem" like it has higher gears, and shorter ones, lower.
And if you are looking at gas mileage and highway driving, the 2.0 will be better. If you want a quick launch in a short race, the 4.0 will be better but worse gas mileage on the highway and higher RPMs at highway speed.
A while back there was a discussion about this same subject and it seems there is a difference in the interpretation and terminology from region to region. Where I grew up, "low" gears were like 4.56, and "high" gears were like 2.75's. But some people said they were taught exactly the opposite. I guess it all depends on what your friends were calling them. Don
Of course, the weight of the vehicle is a factor in choosing a rear end gear, too. Given the same engine, transmission, and tire size, a heavier car will need a somewhat lower gear to gain advantage to get the mass of the vehicle moving, whereas a lighter on could use a higher one, and get the same result. The top gear of the transmission is also a factor in the choice. A transmission with a 1:1 top gear might go well with a 3.00:1 rear gear, and one with a 0.72:1 overdrive might do just as well with a 4.11:1. Given the same equipment, otherwise, the cruise RPM would be about the same (give or take a few RPM), but the launch would be quicker on the overdrive car.
"Where I grew up, "low" gears were like 4.56, and "high" gears were like 2.75's. But some people said they were taught exactly the opposite. I guess it all depends on what your friends were calling them." On that basis I guess they call 1st. gear in a three speed trans high and third gear low?
Nope. The gear ratio of first in any transmission is "lower" than the ratio of the top gears. So we call that one "low gear". Same with the rear end...........at least in my neck of the woods. Don
In a typical transmission "Low" might be 3:1 while "High" would be 1:1. Just to make things more confusing.
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